Lattice Dynamics Modified by Excess Oxygen in Nd - American

Subscriber access provided by CORNELL UNIVERSITY

Article 2

4+#

Lattice Dynamics Modified by Excess Oxygen in NdNiO – Triggering Low Temperature Oxygen Diffusion Adrien Perrichon, Andrea Piovano, Martin Boehm, Mohamed Zbiri, Mark R. Johnson, Helmut Schober, Monica Ceretti, and Werner Paulus

J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/jp510392h • Publication Date (Web): 02 Dec 2014 Downloaded from http://pubs.acs.org on December 15, 2014

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Lattice Dynamics Modified by Excess Oxygen in Nd2NiO4+δ – Triggering Low Temperature Oxygen Diffusion A. Perrichon1, A. Piovano2,*, M. Boehm2, M. Zbiri2, M. Johnson2, H. Schober2, M. Ceretti1, W. Paulus1,* 1

University of Montpellier 2, UMR 5253, ICGM, C2M, CC1504, 5 Place Eugène Batallion, 34095 Montpellier, France 2

Institut Laue-Langevin, 71 avenue des Martyrs 38000 Grenoble, France

Low temperature, oxygen diffusion, lattice dynamics, Nd2NiO4+δ, molecular dynamics, non stoichiometric oxides, inelastic neutron scattering

ABSTRACT. Non-stoichiometric Nd2NiO4+δ shows oxygen ion mobility already at roomtemperature, and as such is a promising materials in the field of solid state ionic conductors. The present work aims to understand the impact of oxygen over-stoichiometry on the lattice dynamics of the Nd2NiO4 framework, and to correlate dynamic instabilities to the anionic mobility at room temperature. We performed neutron time-of-flight spectroscopy experiments coupled with DFT based molecular dynamics calculations on the phases Nd2NiO4.0, Nd2NiO4.10

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 30

and Nd2NiO4.25. Specific signatures in the phonon density of states gave evidence that excess oxygen on interstitial lattice sites activates large displacements of the apical oxygen atoms along the [110] direction, thus favoring their diffusion towards interstitial sites within the rock salt-type layer already at ambient temperature. We implemented a position recurrence method to analyze apical oxygen displacements during the 40 ps timescale of molecular dynamics simulations. The results highlighted that dynamical delocalization of apical oxygen atoms along [110] is necessary to observe diffusion at room temperature, and thus ionic mobility at room-temperature is activated by lattice dynamics.

1. Introduction The development of devices, such as solid state fuel cells, depends on the availability of materials showing high oxygen ion conduction together with low operating temperatures.1,2 Moreover adequate structural and thermochemical stability of the pure ionic conductor membrane and the mixed ionic-electronic electrodes as well as their matching at the interface are essential for the durability of the device.3-7 In this regard, Nd2NiO4+δ system proved to be a good candidate as a stable electrode for intermediate temperature solid state fuel cells.8-11 More intriguing is the fact that Nd2NiO4+δ, like a few other non-stoichiometric oxides derived from the perovskite framework like the Brownmillerite-type Sr(Fe,Co)O2.5 and K2NiF4-type Re2MO4+δ (Re = La, Pr and M = Ni, Cu, Co), shows oxygen ionic mobility in an electrochemical reaction at room-temperature.12-17 This surprising behavior raises questions about the real microscopic transport mechanisms in these classes of materials when the temperature is as low as 300K. Indeed oxygen ions are double negative charged and have large van der Waals radii so that elevated potential barriers normally hinder the hopping processes between inter-atomic sites


2

Page 3 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


at ambient temperature. A microscopic diffusion mechanism, based on the presence of a lowlying phonon mode, has been developed comparing inelastic neutron scattering data and DFT lattice dynamics calculations for the oxygen conductor SrFeO2.5 and the non-conducting CaFeO2.5 isostructural brownmillerites.18 Even if excess oxygen ions can be accommodated in either regular vacancy sites, as is the case for Brownmillerites,14 or interstitial lattice sites, as present in K2NiF4-type structures, ‘phonon assisted diffusion’ allows to understand on an atomic scale how oxygen ion diffusion can be triggered in solid oxides down to ambient temperature. If the trigger for the diffusion process is a low energy lattice mode, the diffusing ion should displace and diffuse following the polarization of the specific low energy phonon. The resulting diffusion path should be therefore strongly anisotropic. Indeed, for several of the mentioned oxides, anisotropic oxygen diffusion has been pointed out.18-22 In all these compounds the oxygen ions organize in a series of different patterns within the host lattice as a function of temperature and oxygen content, leading either to complex long-range commensurate or incommensurate structures and/or short-range disordered arrangements.14,23-27 The present work focuses on Nd2NiO4+δ that, similar to other K2NiF4-type oxides,23,28-30 shows a complex phase diagram at room temperature as a function of the oxygen content δ. Stoichiometric Nd2NiO4.0 adopts at ambient the orthorhombic (LTO) phase with Bmeb spacegroup,30,31 while for δ =0.1 the becomes tetragonal with P42/ncm space-group; finally for fully oxidized Nd2NiO4.25 the symmetry turns out to become orthorhombic with the averaged Fmmm space-group, although the real structure is incommensurate. 32 Concerning the Re2MO4+d systems, the oxygen conductors La2CuO4.07, Pr2NiO4.25 and Nd2NiO4.25 have been reported to show a delocalization of the apical oxygen atoms of the MO6 octahedra on a circle of at least 1Å diameter. In particular Villesuzanne et al.

29

employing


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 30

neutron diffraction on La2CuO4.07 single crystal showed that strong displacements of the apical oxygen atoms towards [100] are present at 20 K, whilst displacements towards [110] and [100] were both found to be present at ambient temperature. The combination with first-principles lattice dynamical calculations, allowed them to point out that the displacements of the apical oxygen atoms to be at least partially of dynamic origin already at ambient temperature. The presence of excess oxygen has been interpreted to contribute essentially to the important shifts of the apical oxygen atoms, closer to the vacant interstitial sites. Moreover, other theoretical studies, using mainly atomistic molecular dynamics, have pointed out that the diffusion process of oxygen ions at higher temperatures develops through successive apical and interstitial sites.3338

Nevertheless the fundamental understanding of the origin of oxygen ion diffusion mechanisms at elevated temperature has been generally undertaken so far by classical approaches, often combined with additional limitations as rigid body tilting of the respective MO6 octahedra. If this simplified approach works well for the range of temperatures where stochastic hopping mobility is the fundamental process, i.e. high temperatures, it fails in depicting the more complicated low temperature scenario, where the strong interplay in between structure and vibrational behavior is believed to be at the origin of the mobility mechanism. These complex oxygen ordering and anisotropic displacement patterns demand a more sophisticated theoretical approach. Indeed it is of utmost importance to understand to which extend one may be able to rationalize oxygen ion diffusion down to ambient temperature by ab initio simulations. For this reason we have investigated the room temperature lattice dynamics of Nd2NiO4+δ system for three distinct stoichiometries (δ = 0, 0.125, 0.25) by means of inelastic neutron scattering and analyzed the results with molecular and lattice dynamics calculations, based on


4

Page 5 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


density functional theory (DFT). We implemented a position recurrence method to precisely map the dynamics connected to apical oxygen as a function of stoichiometry. To the best of our knowledge this is the first time that molecular dynamics results are compared with the real dynamics of these samples, putting on a more solid base the model in which lattice dynamics affects room temperature oxygen mobility.

2. Experimental and Methods 2.1. Samples synthesis Powders of Nd2NiO4+δ were synthetized by solid-state reaction. After having ground powders of Nd2O3 (Alfa Aesar, 0.99) and NiO (Alfa Aesar, 0.99) in stoichiometric proportions, the powders Nd2NiO4+δ with δ = 0, 0.10 and 0.25 were obtained by the solid-state method according to the reaction:

Nd O + NiO Nd NiOδ Due to the hygroscopic nature of the reactants, the Nd2O3 powder was heated under dynamic primary vacuum at 1170K in a tubular furnace overnight, while the NiO powder was dried at 390K in an oven in the same time. The stoichiometric amount of the reactants was first mixed in ethanol then grinded for 4 hours in an agate mechanical mill. The light-blue powder was heated in an alumina crucible under air at 1470K in a tubular furnace overnight, and afterwards furnace cooled to 350K. The resulting black powder was grinded with an agate mechanical mill for 2 hours, pressed into pellets of about 2.0g, and sintered under air at 1470K overnight. This step was repeated twice. In this way the black sintered powder of Nd2NiO4+δ has an oxygen excess δ of about δ =0.23-0.25. The Nd2NiO4.25 powder was obtained from grinding Nd2NiO4+δ and


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 30

sintering it first at 1470K under air in a tubular furnace, then at 670K under a flow of oxygen in a quartz reactor for 48h. The Nd2NiO4.10 powder was obtained from grinding Nd2NiO4+δ and sintering it at 1070K under dynamic primary vacuum in a quartz reactor for 48h. The Nd2NiO4.0 powder was obtained from reduction of Nd2NiO4+δ pellets at 670K under flow of CO/CO2 with ratio 1/10 in a tubular furnace overnight. Nd2NiO4.0 was then grinded in a glove box. 2.2. Experimental technique Inelastic neutron scattering measurements were performed on the direct-geometry cold-neutron time-of-flight time-focusing spectrometer IN6 at the Institut Laue Langevin (Grenoble, France). Data were collected at T=150, 230 and 310K, in the upscattering mode using an incident wavelength of λ=4.14 Å, leading to a resolution of 0.17 meV at the elastic line. The time focusing was set to 6.7 meV, giving very good resolution below 30 meV. About 15 g of polycrystalline samples of Nd2NiO4+δ (δ =0, 0.10, 0.25) were held in thin niobium sample holders that were fixed to the sample stick of a standard fournace. Standard corrections including detector efficiency calibration and background substraction were performed. The data analysis was done using ILL software tools.39 At the neutron wavelength λ=4.14 Å, the IN6 angular coverage (17 to 114°) corresponds to a maximum momentum transfer of Q~2.6 Å-1. In order to minimize the contamination of phonon spectra by magnetic scattering, only the high-Q region was considered (1.8 - 2.6 Å-1). Therefore, after correction for energy-dependent detector efficiency, the one-phonon generalized phonon density of states (GDOS) was obtained from the angle-integrated data over the above-mentioned high-Q region of the (Q,ω) space, using the incoherent approximation in the same way as in previous works dealing with phonon dynamics.40-43 2.3. Computational details


6

Page 7 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


We performed molecular dynamics (MD) ab initio DFT calculations, at room-temperature, using the code VASP.44,45, in the NVT ensemble in a 40 ps time window. To take in account for long range Culomb interaction a 2 x 2 x1 supercell has been employed, with a total of 112 atoms for Nd2NiO4.0 model. Projected augmented wave (PAW) potentials were chosen for the ionic core-valence interactions and the Perdew, Burke and Ernzerhof (PBE)46 scheme for the generalized gradient approximation (GGA) was used for the exchange-correlation potential. For all elements PBE pseudo-potentials were used, while frozen 4f orbitals have been included only for the neodymium. We performed both spin-polarized and non-spin polarized calculations on the low-temperature tetragonal phase of stoichiometric Nd2NiO4.0. Following the magnetic structure reported in literature,30 collinear magnetism has been added for Ni ions only. Because Nd magnetic order is not present at 300K, a simplified basis with frozen 4f orbitals basis has been employed. On the contrary, neither Nd2NiO4.10 nor Nd2NiO4.25 show any specific magnetic order since suppressed by excess oxygen. Anyhow we modeled the over-stoichiometric systems using PBE+U formalism to take in account for the correct electronic ground state. The simplified (rotationally invariant) approach to the DFT+U, introduced by Dudarev et al.47 has been employed, for which Ueff = U – J. The Hubbard corrective term with parameters U=7.0 eV and J=0.9 eV have been used for the Nickel ions. Similar values for U and J have been successfully employed for DFT+U calculations on La5/3Sr1/3NiO4 (U = 8 eV and J = 0.8 eV)48, on LaNiO3 (Ueff = U – J = 6 meV as from Dudatev approximation)49 and on K2NiF4 (U= 7 eV and J = 1.06 eV)50. The vibrational density of states (vDOS) was calculated from the velocity autocorrelation function using the nMOLDYN software.51 The vDOS was then weighted by the coherent neutron scattering cross-sections and convoluted with the instrument resolution.


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 30

For mode eigenvector analysis, we performed additional phonon calculations on Nd2NiO4.0 using the direct method with ab initio calculated Hellmann-Feynman forces. The dynamical matrix diagonalization and the calculation of phonon dispersion curves and phonon density of states at T=0K were performed with PHONON.52 2.4. Positional Recurrence Maps Positional Recurrence Maps (PRM) have been calculated from molecular dynamics trajectories at room-temperature. They look similar to nuclear density maps obtained from maximum entropy methods applied to diffraction patterns,28 but in this case we point out only the dynamical contribution specific of the single particle motion. Indeed the outputs are 2D maps that represent the projection of atomic displacements from center-of-masses of considered atoms (apical oxygen in our case), on unitary vectors of the cell. Since displacements are considered instead of positions, static deformations are not taken into account. As such, the delocalization, i.e. the shape of the pattern, is purely dynamical. The construction process is basically a cumulative sum over the molecular dynamics trajectory, and can be described as: , !, "#$,% = ∑$ ∑%)12'($ ) , !) , ") # − ($

+.-... , !+.-... , "+.-... #

+ /$ 0

Eq. 1

With n(x,y,z)j,T the positional recurrence map of atoms j limited in time to the simulation length T. The atomic position of atom j at step t is pj(xt,yt,zt), while its center of mass position at t=0 is ($

+.-... , !+.-... , "+.-... #.

An additional constant Cj is used to superimpose equivalent atoms

taking account of the average symmetry. In our case we extracted the position recurrence maps for the oxygen species occupying the apical position at the beginning of the molecular dynamics simulation.


8

Page 9 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. Projection onto the ab plane of the real apical oxygen atoms position from molecular dynamics trajectories of Nd2NiO4.0 (a,c) and the corresponding position recurrence maps (PRM) (c,d). (a,b): calculation considering small displacements around equilibrium position. (c,d): calculation with large atomic displacements. (a,c) are plots in a standard Cartesian space where static deformation and the atomic motion are merged. (b,d) are plots in atomic displacement space where the initial apical oxygen atoms positions merged to a single starting point (xc.o.m.,yc.o.m.) and the displacements are defined as differences from this initial position (xtxc.o.m.,yt-yc.o.m.) (see Eq. 1). This allows highlighting the atomic motion only, disregarding static deformations. As an example in Figure 1a,c we show the standard projection onto the ab plane of the real apical oxygen atoms positions summed over the whole MD time of tetragonal (LTT) Nd2NiO4.0 structure, while in Figure 1b,d the corresponding position recurrence map. We consider first the case when small displacements around equilibrium position are present as reported in Figure 1a,b. In the real structure the projected position onto the (a,b) Cartesian plane of apical oxygen is split due to a distortion of the octahedra along the [110] and the [1140] directions and so we


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 30

observe four spot of high position density in correspondence of apical oxygen positions (Figure 1a). On the contrary, if we group the position of apical oxygen to a common single starting point and we calculate only atomic displacements from this defined initial position, the four spots are reported to a single one in the Displacement space (ua, ub), as observed in Figure 1b. The importance of PRM method comes clear at the time when the atomic displacements come wider as in cases depicted in Figure 1c,d. Indeed, the pattern in Cartesian space would contain both the static deformation and the dynamical motion (Figure 1c), resulting in a smeared and confused picture, while in the displacement space only the dynamical motion is represented (Figure 1d) and the polarization of the displacement scheme is clearly pointed out. It is worth noticing that, even if spots away from the center of the PRM results artificially split as consequence of the treatment, the on-site atomic motion, i.e. atomic motion around the central position, is much clearer to interpret.

3. Results and Discussion Nd2NiO4.0 has been shown to be magnetically ordered at 300K, with the presence of a collinear antiferromagnetic ordering of Ni2+ magnetic moments. 30 The out-of plane component of internal magnetic field of Nd3+ ions develops only below 130K.31 On the contrary, neither Nd2NiO4.10 nor Nd2NiO4.25 show any specific magnetic order since suppressed by excess oxygen.30 For this reason collinear magnetism of Ni ions has been added only for the stoichiometric Nd2NiO4.0, while no specific spin arrangement has been included for the over-stoichiometric cases. Because Nd magnetic order is not present at 300K, a simplified basis with frozen 4f orbitals basis has been employed.


10

Page 11 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Cell parameters of Nd2NiO4+δ obtained from DFT optimization calculations at 0 K and experimental ones found in literature are reported in Table 1. Only for the stoichiometric case low temperature data are present (1.5 K); then direct comparison can be made exactly only for this case. Taking the low-temperature P42/ncm (T-d0) phase as model, the calculated cell parameters of Nd2NiO4.0 without magnetism were in fair agreement with the experimental ones at low-temperature, while the addition of collinear magnetism improved the overall match, especially for the c-axis. In principle, for the subsequent MD simulations at 300K, we should have used the room-temperature Bmeb phase of Nd2NiO4.0 (O-d0). Nevertheless, our calculations showed that the Bmeb symmetry does not present the ground state of Nd2NiO4.0 at 0 K; as a consequence the low temperature model with P42/ncm symmetry has been aklso adopted as starting point for the MD. Similarly, the reported Fmmm phase of Nd2NiO4.25 (O-d25), showing small orthorhombic splitting, has been modeled in a tetragonal cell (T-d25). For Nd2NiO4.10 the agreement between experimental and calculated cell parameters is not as good. This reduced matching is understandable by the fact that there are in principle four different ways to arrange extra oxygen inside Nd2NiO4.10, while we considered only the one that turn out to be the most stable, i.e. lowest ground state energy, after optimization. Table 1. Cell parameters of Nd2NiO4.0 (d0), Nd2NiO4.10 (d10) and Nd2NiO4.25 (d25), in orthorhombic (O) or tetragonal cell (T), from ab initio DFT calculation and neutron diffraction. Experiments at T=300Ka

Experiment at T=1.5Ka

Non-magnetic calculations

Magnetic calculation

Phase

O-d0

T-d10

O-d25

T-d0

T-d0

T-d10

T-d25

T-d0

a (Å)

5.3759(5)

5.4549(1)

5.3688(5)

5.480(1)

5.3734

5.3328

5.4557

5.5146

b (Å)

5.5759(5)

-

5.4431(6)

-

-

-

-

5.5168

c (Å)

12.104(1)

12.2204(1)

12.351(2)

12.057(3)

12.7357

12.6493

12.263

12.233


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

a

Page 12 of 30

Ref 30

The experimental c-axis length for Nd2NiO4.0 is shorter than for Nd2NiO4.25. We were able to reproduce the shortening in the c-axis length for Nd2NiO4.0 compared to Nd2NiO4.25 with DFT only performing spin polarized calculations for Nd2NiO4.0. Instead the Nd2NiO4.10 c-axis value is far to be intermediate respect to the other two stoichiometries. We can thus suppose that, even if the Nd2NiO4.10 has no long range magnetic order, some short range antiferromagnetic coupling still persists. To study the lattice dynamics present in the regular host system (δ =0) and the effect of oxygen excess (δ =0.10, 0.25) we performed time of flight inelastic neutron scattering experiments on powder polycrystalline samples. Figure 2a shows a comparison of the experimental gDOS extracted from the inelastic neutron spectra for the three different oxygen contents at T=310K. We distinguish three energy ranges of interest in the stoichiometric Nd2NiO4.0 sample (black dots in Figure 2a): a region from 5 to 11 meV with a shoulder component (feature A), a region from 11 to 16 meV with a large bump (feature B) and a region from 16 to 21 meV with an intense peak (feature C). With increasing stoichiometry up to Nd2NiO4.25 (from black to blue dots in Figure 2a), the component A clearly decreases in intensity, while the feature C shifts towards higher energies and loses intensity. As the feature B does not change in intensity while components A and C decrease, the overall effect is a slight, relative increase of the amount of vibrational states in this region B. As expected the case of Nd2NiO4.1 (green dots in Figure 2a) is intermediate to the other two in both intensity variation and energy shifts, looking more similar to the Nd2NiO4.25 case.


12

Page 13 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. (a) Generalized phonon density of states collected on IN6 spectrometer of Nd2NiO4.0 (black), Nd2NiO4.10 (green) and Nd2NiO4.25 (blue) at 310K. (b) Vibrational density of states calculated from ab initio molecular dynamics; same color legend as (a). As a guide for the eyes, the increase, decrease and shift of the main features are marked with red arrows Ab–initio MD calculations have been performed at room-temperature for the three different oxygen contents, and the calculated gDOS are shown in Figure 2b for comparison with the experimental ones. The main trends observed in experimental data when moving from Nd2NiO4.0 to Nd2NiO4.25 are reproduced, even though the match with experiment is not perfect due to


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 30

different limitations: i) the limited number of atoms that can be simulated by DFT method (< few hundreds of atoms), resulting in a simplified structural model; ii) the intrinsic limitation of DFT method concerning electron-electron correlations. As already mentioned, for Nd2NiO4.10 the level of agreement with experiment is lower due to the fact that we used as model only one of the four possible configuration of inclusion of excess oxygen, the one with the lowest ground state energy after optimization. To unambiguously attribute phonon frequencies to specific vibrational patterns we performed additional calculations to obtain normal modes by the direct method. However, we observed that the room-temperature Bmeb structure (LTO) is not stable below T=130K 30 and led to imaginary modes in the calculation. To obtain all phonon modes positive, the Bmeb structure has been replaced by the low-temperature P42/ncm structure (LTT). While the LTO and LTT structures have different lattice dynamics, especially concerning modes affected by the tilting scheme and the loss of orthorhombicity, the mode of lowest energy at the Y point of the Brillouin Zone concerns the [010] tilting similar to any La2NiO4-related structures.53,54 Thus we can assert that feature A represents states with displacements mainly developing along [100] direction, while feature B concerns the ones along [110]. Feature C is instead related to the octahedral modes and in particular the stretching along the c direction. The observed variations in function of excess oxygen reflect a decrease of spectral weight for vibrational modes with displacement pattern along [100] and a concomitant increase for modes with displacement pattern along [110]. Moreover the introduction of interstitial oxygen constrains the octahedral stretching mode which consequently hardens and dampens. More precisely, as δ increases, the oxidation of Ni2+ to Ni3+ slightly shortens the Ni-Oap bond length, while the excess oxygen atoms force an elongation of the stacking-axis, thus extending the rock-


14

Page 15 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


salt layer where oxygen is diffusing. Moreover, the modification of the tilt pattern from [100] to [110] favors the displacement of the apical oxygen atom to the rock-salt layer. These two effects relate the observed damping of the modes A and C to enhanced oxygen mobility. If our interpretation is correct and oxygen diffusion is lattice activated at ambient temperature and is thermally activated at high temperature, the influence of low energy modes should diminish when increasing temperature until it completely disappears when high temperature stochastic hopping process dominates. This seems not surprising as the influence of anisotropic displacement modes become less important with respect to the thermal activation in the high temperature regime.

Figure 3: experimental phonon density of states obtained at 1073K on Nd2NiO4+δ systems with δ =0 (black dots) and δ =0.1 (red dots). δ =0.25 stoichiometry is not stable at high temperature in dynamics vacuum of fournace used and reduces down to δ =0.1 at 1073K. This is what experimentally we observed comparing vDOS obtained at room temperature and shown in Figure 2 and those obtained at 1073K and shown in Figure 3. Indeed at room temperature different stoichiometries present quite different lattice dynamics and these


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 30

differences can be related to the onset of oxygen diffusion mechanism, as will be shown shortly after. On the contrary, at high temperatures, different stoichiometries show an almost identical vDOS evidencing any contribution from lattice dynamics to the oxygen diffusion process. This goes along with the fact that the chemical diffusion coefficient on the similar system Pr2NiO4+δ has been simulated to be independent of δ above 800K for any δ >0.35 The variations in the lattice dynamics can be directly related to the structural deformations imposed on the host lattice by a simple model containing the inclusion of additional oxygen. In the stoichiometric case the structure is described in the Bmeb space-group, with a tilt pattern of NiO6 octahedron along the [100] direction. Upon filling the interstitial tetrahedral sites of the rock-salt layers, the additional oxide ions deform the first shell of neighboring apical oxygen atoms, forcing a tilt from the [100] to the [110] direction.29 As schematized in Figure 4, for an oxygen content of δ =0.10, about one excess oxygen is present for 16 apical oxygen atoms, forcing a quarter of the apical oxygen atoms along [110] while the rest may still follow the [010] tilt direction. Reaching the content δ =0.25, half of the apical oxygen atoms are affected by this additional tilt. One therefore expects a perturbation of the tilting mode along the [100] directions leading to a hardening and possible damping with increasing excess oxygen content, while the [110] mode should, on the contrary, get softened. Such a picture is directly reflected by the lowlying energy part of the phonon calculations showing important contribution of the [100] tilt mode at 5.3 meV, while the spectral weight of the [110] tilting is located around 13 meV.


16

Page 17 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. Scheme of the tilt pattern in the Bmeb space-group of (a) stoichiometric Nd2NiO4.0, and (b) Nd2NiO4+δ with excess oxygen in interstitial site. Apical oxygen atoms in the plane below the interstitial site are represented in red (z≈0.17), and in the plan above in blue (z≈0.33). Excess oxygen in interstitial site is represented in green (z=0.25). The first shell of apical oxygen atoms surrounding the interstitial is deformed from [100] to [110]. In order to de-correlate the effects of excess oxygen on Ni-Oap bond length and NiO6 tilting pattern we performed MD calculations for different lengths of the stacking-axis parameter (caxis) with respect to the calculated optimal value. PRM maps have been calculated for the whole set of simulations to get a qualitative picture of the effect of excess oxygen on the lattice dynamics. The PRM patterns projected onto the ab plane for different lengths of the stacking-axis parameter and the various excess oxygen contents are shown in Figure 5. Each pattern is calculated from the displacements of the oxygen atoms in Oap sites with respect to the starting point of the calculation and projected on the (001) plane in a 40 ps time window. In the stoichiometric Nd2NiO4.0 case, the apical oxygen PRM with a c-axis corresponding to the optimized value from calculations (see Table 1) presents a cross shape with preferred displacements in the [100] direction as shown in (Figure 5d).This is expected since the LTO structure, without the deformations imposed by interstitial oxygen atoms (see Figure 4), must have the tilt pattern of apical oxygen along [100]. In the case of a contracted c-axis parameter (Figure 5a), the apical oxygen PRM is completely isotropic, which means that the apical oxygen is rigidly held within the NiO6 octahedron. Assuming an elongated c-axis parameter (Figure 5g), we observe a shifting of the displacement from the [100] towards [110] direction, hence an activation of the [110] tilt mode.


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 30

Figure 5. Positional recurrence maps: displacement vectors of apical oxygen atoms in the Nd2O2 rocksalt layer from center-of-mass positions projected on unitary vectors (a,b), with respect to the conventional F-cell. PRM are calculated from ab initio molecular dynamics at 310K, of (Fig 3a, 3d, 3g) Nd2NiO4.0, (Fig 3b, 3e, 3h) Nd2NiO4.10, (Fig 3c, 3f, 3i) Nd2NiO4.25, with (Fig 3a-c) reduced c-axis parameter by 0.5Å, (Fig 3d-f) optimal c-axis parameter, and (Fig 3g-i) elongated c-axis parameter by 0.5Å. The color scale is logarithmic. Each PRM is cut in space to the conventional F-cell (black border).


18

Page 19 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


For the Nd2NiO4.25 case, the PRM of apical oxygen with reduced c-axis parameter (Figure 5c) shows [110] delocalization of the inner pattern, which comes from the first neighbor interaction of NiO6 and interstitial oxygen atoms. A smaller delocalization is also observed in the outer shell, and comes from the second neighbor interaction between the apical oxygen and different combinations of the several interstitial oxygen atoms. In this rigid case, most of the freedom of NiO6 octahedron is pinned by the interstitial oxygen. Considering the optimized c-axis parameter (Figure 5f), the second neighbor interaction disappears and the [110] pathway is broadened. For an elongated c-axis parameter (Figure 3i), the apical oxygen density shows an even broader [110] delocalization. For the intermediate Nd2NiO4.10 case, the positional recurrence pattern of the apical oxygen atom with an optimal stacking-axis parameter (Figure 5e) shows both [100] and [110] delocalization. This is consistent with the above mentioned quarter filling of the interstitial sites for δ =0.1, which means that 75% of apical oxygen atoms have ‘normal’ dynamics and contribute to [100] delocalization, and 25% of them experience a [110] deformation, which activates the [110] delocalization. It is worth noticing that the small satellites in the outer shell come from diffusion events of oxygen atoms from the apical to the interstitial site. In the case of a reduced stacking-axis parameter (Figure 5b), a similar PRM is formed, yet with less [100] displacement events and pronounced [110] delocalization. In this rigid regime, every NiO6 octahedron is strongly dependent on its neighbors, which means that the [110] strained apical oxygen drives the free apical oxygen from [010] to [110]. With an elongated stacking-axis parameter (Figure 5h), the octahedra become less dependent, which leads to a renewed [100] delocalization, a strong [110] delocalization from interstitial oxygen, and an easy diffusion between apical and interstitial sites.


19


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 30

Figure 6. Detail of the rock-salt layer of Nd2NiO4.10 supercell in the T=310K molecular dynamics. Wired green spheres represent Nd+3 ions, wired red spheres O-2 ions in apical sites and plain red sphere O-2 ion in interstitial site. Atoms are draw at their initial positions. Grey clouds represent the ensemble of positions occupied by the atoms over the 40ps of the molecular dynamics. Connected clouds from apical to interstitial sites are marked with a yellow line, and evidence oxygen mobility. From MD calculations it is also possible to directly extract the computed diffusion pathway of mobile oxygen species. We found that the diffusion pathway of non-stoichiometric Nd2NiO4+δ clearly pass through interstitial sites and is similar to the one reported for isostructural La2CoO4+δ and La2NiO4+δ.33-38 Figure 6 shows the rock-salt layer of the superstructure we used to simulate the Nd2NiO4.10 phase. The mechanism of diffusion involves both apical and interstitial oxygen atoms with a defined scheme: i) one of the apical oxygen atoms closest to the excess oxygen diffuses away to a vacant interstitial site; ii) then the former interstitial oxygen diffuses to the newly vacant apical site. Such diffusion is confined in the rock-salt layer with jump only along 61107. We note that in the absence of excess oxygen in the interstitial site of a rock-salt layer, e.g. for Nd2NiO4.0, no diffusion events occur in this layer.

4. Conclusions


20

Page 21 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


In this work we investigated the effect that excess oxygen, located on interstitial lattice sites, has for the lattice dynamics of Nd2NiO4+δ and its added impact to activate low temperature oxygen mobility via a phonon assisted diffusion mechanism. Inelastic neutron scattering data on Nd2NiO4.0, Nd2NiO4.10 and Nd2NiO4.25, have been analyzed combining first-principle ab initio phonon calculations together with molecular dynamics simulations. From the MD simulations, which were treated in detail by positional recurrence map analysis on a 40 ps time scale, we were able to identify the different tilting dynamics of the NiO6 octahedra and resulting displacements of the apical oxygen atoms and their impact on the oxygen diffusion process at ambient temperature. With increasing oxygen content the generalized density of states of Nd2NiO4+δ, as obtained by INS, show a damping of the [100] tilt mode of NiO6 octahedra and an activation of the [110] tilt mode, resulting in large displacement amplitudes towards adjacent interstitial lattice sites. This effect dynamically favors oxygen diffusion between apical and interstitial sites already at ambient temperature. We were able to reproduce the same dynamics with our molecular dynamics simulations and clarify that the apical oxygen displacements arise from a competitive interplay in between variations of the c-axis parameter length and doping concentration of the excess oxygen atoms on interstitial lattice sites. In this way the influence of the expansion of the c-axis parameter and extra oxygen stoichiometry on room temperature oxygen diffusion can be summarized as follows: i) a shortening of the c-axis parameter leads in fine to an obstruction of any diffusion event, freezing in the libration modes of the NiO6 octahedra in its given tilt configuration, implying a strong localization of the apical oxygen atoms; ii) an elongation of the c-axis parameter naturally facilitates the delocalization of the apical oxygen atoms, thus allowing a free rotation of the NiO6 octahedra; furthermore, it favors the displacements of the apical oxygen towards the vacant


21


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 30

interstitial lattice site, showing a drift from [100] to [110] going along with the increase of the caxis parameter; iii) excess oxygen in interstitial sites strongly activates the [110] displacements of apical oxygen atoms. We can thus conclude that the extra oxygen stoichiometry δ enhances the activation apical oxygen displacements along [110], which finally enable oxygen mobility down to ambient temperature for sufficiently high excess oxygen doping. The fact that Nd2NiO4+δ can uptake a huge amount of extra oxygen atoms, δmax = 0.25, and that this amount is still important even at higher temperatures (δ ~ 0.15 at 800K), plays a decisive role for promoting oxygen diffusion in the lower temperature range and in particular at ambient temperature. This seems to be a principal difference for oxygen diffusion behavior of K2NiF4 type oxides especially when going to high temperatures, where the chemical diffusion coefficient of Pr2NiO4+δ has been simulated to be independent of δ above 800K in its tetragonal symmetry.35 This seems not surprising as the influence of anisotropic displacement modes has been shown experimentally to become less dominating respect to thermal activation in the high temperature regime. Activation of oxygen diffusion in Nd2NiO4+δ at ambient temperature just seems to be highly correlated with the amount of extra oxygen in interstitial sites and with the large displacements of the apical oxygen atoms towards interstitial sites themselves.

AUTHOR INFORMATION Corresponding Author *A. Piovano: [email protected] . * W Paulus: [email protected] ACKNOWLEDGMENT


22

Page 23 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


We greatly appreciate a PhD fellowship offered by the University of Montpellier 2 for A.P. M.C. and W.P. are grateful for financial support obtained through the ANR project FUSTOM (ANR- 08-BLAN-0069) REFERENCES (1) Fergus, J. W.; Electrolytes for solid oxide fuel cells J. Power Sources 2006, 162, 30-40. (2) Brandon, N. P.; Skinner, S.; Steele, B. C. H.; Recent advances in materials for fuel cells Ann. Rev. Mater. Res. 2003, 33, 183-213. (3) Yokokawa, H.; Tu, H. Y.; Iwanschitz, B.; Mai, A.; Fundamental mechanisms limiting solid oxide fuel cell durability J. Power Sources 2008, 182, 400-412. (4) Dailly, J.; Marrony, M.; BCY-based proton conducting ceramic cell: 1000 h of long term testing in fuel cell application J. Power Sources 2013, 240, 323-327. (5) Mesguich, D.; Bassat, J. M.; Aymonier, C.; Brull, A.; Dessemond, L.; Djurado, E.; Influence of crystallinity and particle size on the electrochemical properties of spray pyrolyzed Nd2NiO4+delta powders Electrochim. Acta 2013, 87, 330-335. (6) Montenegro-Hernandez, A.; Mogni, L.; Caneiro, A.; Microstructure and reactivity effects on the performance of Nd2NiO4+delta oxygen electrode on Ce0.9Gd0.1O1.95 electrolyte Int. J. Hydrog. Energy 2012, 37, 18290-18301. (7) Montenegro-Hernandez, A.; Vega-Castillo, J.; Mogni, L.; Caneiro, A.; Thermal stability of Ln(2)NiO(4+delta) (Ln: La, Pr, Nd) and their chemical compatibility with YSZ and CGO solid electrolytes Int. J. Hydrog. Energy 2011, 36, 15704-15714.


23


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 30

(8) Chauveau, F.; Mougin, J.; Bassat, J. M.; Mauvy, F.; Grenier, J. C.; A new anode material for solid oxide electrolyser: The neodymium nickelate Nd2NiO4+delta J. Power Sources 2010, 195, 744-749. (9) Egger, A.; Bucher, E.; Sitte, W.; Oxygen exchange kinetics of the IT-SOFC cathode material Nd2NiO4+delta and comparison with La0.6Sr0.4CoO3-delta J. Electrochem. Soc. 2011, 158, B573-B579. (10) Hanifi, A. R.; Torabi, A.; Chen, X. Y.; Hill, S.; Sarkar, P.; Etsell, T. H.; Development of redox resistant fully infiltrated tubular SOFCs J. Electrochem. Soc. 2014, 161, F391-F397. (11) Yamada, A.; Suzuki, Y.; Saka, K.; Uehara, M.; Mori, D.; Kanno, R.; Kiguchi, T.; Mauvy, F.; Grenier, J. C.; Ruddlesden-Popper-type epitaxial film as oxygen electrode for solid-oxide fuel cells Adv. Mater. 2008, 20, 4124-+. (12) Bhavaraju, S.; Dicarlo, J. F.; Scarfe, D. P.; Yazdi, I.; Jacobson, A. J.; Electrochemical intercalation of oxygen in Nd2NiO4+x (0-=< x =< 0.18) at 298-K Chem. Mat. 1994, 6, 21722176. (13) Bhavaraju, S.; Dicarlo, J. F.; Yazdi, I.; Jacobson, A. J.; Feng, H. H.; Li, Z. G.; Hor, P. H.; Electrochemical intercalation of oxygen in Lanthanum Copper-Oxide at ambient-temperature Mater. Res. Bull. 1994, 29, 735-742. (14) Le Toquin, R.; Paulus, W.; Cousson, A.; Prestipino, C.; Lamberti, C.; Time-resolved in situ studies of oxygen intercalation into SrCoO2.5, performed by neutron diffraction and X-ray absorption spectroscopy J. Am. Chem. Soc. 2006, 128, 13161-13174.


24

Page 25 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(15) Nemudry, A.; Goldberg, E. L.; Aguirre, M.; Alario-Franco, M. Á.; Electrochemical topotactic oxidation of nonstoichiometric perovskites at ambient temperature Solid State Sci. 2002, 4, 677-690. (16) Piovano, A.; Agostini, G.; Frenkel, A. I.; Bertier, T.; Prestipino, C.; Ceretti, M.; Paulus, W.; Lamberti, C.; Time resolved in situ XAFS study of the electrochemical oxygen intercalation in SrFeO2.5 Brownmillerite structure: comparison with the homologous SrCoO2.5 system J. Phys. Chem. C 2011, 115, 1311-1322. (17) Yazdi, I.; Bhavaraju, S.; Dicarlo, J. F.; Scarfe, D. P.; Jacobson, A. J.; Electrochemical intercalation of oxygen in La2NiO4+X - phase-separation below ambient-temperature Chem. Mat. 1994, 6, 2078-2084. (18) Paulus, W.; Schober, H.; Eibl, S.; Johnson, M.; Berthier, T.; Hernandez, O.; Ceretti, M.; Plazanet, M.; Conder, K.; Lamberti, C.; Lattice dynamics to trigger low temperature oxygen mobility in solid oxide ion conductors J. Am. Chem. Soc. 2008, 130, 16080-16085. (19) Auckett, J. E.; Studer, A. J.; Pellegrini, E.; Ollivier, J.; Johnson, M. R.; Schober, H.; Miiller, W.; Ling, C. D.; Combined experimental and computational study of oxide ion conduction dynamics in Sr2Fe2O5 Brownmillerite Chem. Mat. 2013, 25, 3080-3087. (20) Bassat, J. M.; Burriel, M.; Wahyudi, O.; Castaing, R.; Ceretti, M.; Veber, P.; Weill, I.; Villesuzanne, A.; Grenier, J. C.; Paulus, W.et al.; Anisotropic oxygen diffusion properties in Pr2NiO4+delta and Nd2NiO4+delta single crystals J. Phys. Chem. C 2013, 117, 26466-26472.


25


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 30

(21) Inoue, S.; Kawai, M.; Ichikawa, N.; Kageyama, H.; Paulus, W.; Shimakawa, Y.; Anisotropic oxygen diffusion at low temperature in perovskite-structure iron oxides Nat. Chem. 2010, 2, 213-217. (22) Yamada, A.; Saka, K.; Uehara, M.; Taminato, S.; Kanno, R.; Mauvy, F.; Grenier, C.; Anisotropic catalytic activity of the orientation controlled Nd2NiO4 (+) (delta)/YSZ heteroepitaxial system for SOFC cathode Electrochem. Commun. 2010, 12, 1690-1693. (23) Le Toquin, R.; Paulus, W.; Cousson, A.; Dhalenne, G.; Revcolevschi, A.; Interstitial and apical oxygen order-disorder in La(2)CoO(4+delta) observed by single-crystal neutron and X-ray diffraction Physica B 2004, 350, E269-E272. (24) Le Dreau, L.; Prestipino, C.; Hernandez, O.; Schefer, J.; Vaughan, G.; Paofai, S.; PerezMato, J. M.; Hosoya, S.; Paulus, W.; Structural modulation and phase transitions in La2CoO4.14 investigated by synchrotron X-ray and neutron single-crystal diffraction Inorg. Chem. 2012, 51, 9789-9798. (25) Tranquada, J. M.; Kong, Y.; Lorenzo, J. E.; Buttrey, D. J.; Rice, D. E.; Sachan, V.; Oxygen intercalation stage ordering, and phase-separation in La2NiO4+delta with 0.05 =< delta =< 0.11 Phys. Rev. B 1994, 50, 6340-6351. (26) Rice, D. E.; Buttrey, D. J.; An X-Ray-diffraction study of the oxygen-content phasediagram of La2NiO4+delta J. Solid State Chem. 1993, 105, 197-210. (27) Puche, R. S.; Fernandez, F.; Carvajal, J. R.; Martinez, J. L.; Magnetic and X-raydiffraction characterization of stoichiometric Pr2NiO4 and Nd2NiO4 oxides Solid State Commun. 1989, 72, 273-277.


26

Page 27 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(28) Paulus, W.; Cousson, A.; Dhalenne, G.; Berthon, J.; Revcolevschi, A.; Hosoya, S.; Treutmann, W.; Heger, G.; Le Toquin, R.; Neutron diffraction studies of stoichiometric and oxygen intercalated La2NiO4 single crystals Solid State Sci. 2002, 4, 565-573. (29) Villesuzanne, A.; Paulus, W.; Cousson, A.; Hosoya, S.; Le Dreau, L.; Hernandez, O.; Prestipino, C.; Houchati, M. I.; Schefer, J.; On the role of lattice dynamics on low-temperature oxygen mobility in solid oxides: a neutron diffraction and first-principles investigation of La2CuO4+delta J. Solid State Electrochem. 2011, 15, 357-366. (30) Rodriguezcarvajal, J.; Fernandezdiaz, M. T.; Martinez, J. L.; Fernandez, F.; Saezpuche, R.; Structural phase-transitions and 3-dimensional magnetic-ordering in the Nd2NiO4 oxide Europhys. Lett. 1990, 11, 261-268. (31) Batlle, X.; Obradors, X.; Martinez, B.; Magnetic-interactions, weak ferromagnetism, and field-induced transitions in Nd2NiO4 Phys. Rev. B 1992, 45, 2830-2843. (32) Fernández-Díaz, M. T.; Martínez, J. L.; Rodríguez-Carvajal, J.; High-temperature phase transformation of oxidized R2NiO4+δ(R=La, Pr and Nd) under vacuum Solid State Ionics 1993, 63–65, 902-906. (33) Kushima, A.; Parfitt, D.; Chroneos, A.; Yildiz, B.; Kilner, J. A.; Grimes, R. W.; Interstitialcy diffusion of oxygen in tetragonal La2CoO4+delta Phys. Chem. Chem. Phys. 2010, 13, 2242-2249. (34) Minervini, L.; Grimes, R. W.; Kilner, J. A.; Sickafus, K. E.; Oxygen migration in La2NiO4+delta J. Mater. Chem. 2000, 10, 2349-2354.


27


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 30

(35) Parfitt, D.; Chroneos, A.; Kilner, J. A.; Grimes, R. W.; Molecular dynamics study of oxygen diffusion in Pr2NiO4+delta Phys. Chem. Chem. Phys. 2010, 12, 6834-6836. (36) Tealdi, C.; Ferrara, C.; Mustarelli, P.; Islam, M. S.; Vacancy and interstitial oxide ion migration in heavily doped La2-xSrxCoO4 +/-delta J. Mater. Chem. 2012, 22, 8969-8975. (37) Naumovich, E. N.; Kharton, V. V.; Atomic-scale insight into the oxygen ionic transport mechanisms in La2NiO4-based materials Theochem-J. Mol. Struct. 2010, 946, 57-64. (38) Chroneos, A.; Parfitt, D.; Kilner, J. A.; Grimes, R. W.; Anisotropic oxygen diffusion in tetragonal La2NiO4+delta: molecular dynamics calculations J. Mater. Chem. 2010, 20, 266-270. (39) LAMP: Large Array Manipulation Program at ILL. (40) Zbiri, M.; Mittal, R.; Rols, S.; Su, Y. X.; Xiao, Y. G.; Schober, H.; Chaplot, S. L.; Johnson, M. R.; Chatterji, T.; Inoue, Y.et al.; Magnetic lattice dynamics of the oxygen-free FeAs pnictides: how sensitive are phonons to magnetic ordering? J. Phys.-Condes. Matter 2010, 22, 315701. (41) Zbiri, M.; Mutka, H.; Johnson, M. R.; Schober, H.; Payen, C.; Phonon control of magnetic relaxation in the pyrochlore slab compounds SrCr9xGa12-9xO19 and Ba2Sn2ZnCr7xGa107xO22 Phys. Rev. B 2010, 81, 104414. (42) Zbiri, M.; Schober, H.; Choudhury, N.; Mittal, R.; Chaplot, S. L.; Patwe, S. J.; Achary, S. N.; Tyagi, A. K.; High-temperature phonon spectra of multiferroic BiFeO3 from inelastic neutron spectroscopy Appl. Phys. Lett. 2012, 100, 142901. (43) Zbiri, M.; Schober, H.; Johnson, M. R.; Rols, S.; Mittal, R.; Su, Y. X.; Rotter, M.; Johrendt, D.; Ab initio lattice dynamics simulations and inelastic neutron scattering spectra for


28

Page 29 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


studying phonons in BaFe2As2: effect of structural phase transition, structural relaxation, and magnetic ordering Phys. Rev. B 2009, 79, 064511. (44) Kresse, G.; Furthmuller, J.; Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set Phys. Rev. B 1996, 54, 11169-11186. (45) Kresse, G.; Hafner, J.; Ab-initio molecular-dynamics for open-shell transition-metals Phys. Rev. B 1993, 48, 13115-13118. (46) Perdew, J. P.; Burke, K.; Ernzerhof, M.; Generalized gradient approximation made simple Phys. Rev. Lett. 1996, 77, 3865-3868. (47) Dudarev, S. L.; Botton, G. A.; Savrasov, S. Y.; Humphreys, C. J.; Sutton, A. P.; Electronenergy-loss spectra and the structural stability of nickel oxide: An LSDA+U study Phys. Rev. B 1998, 57, 1505-1509. (48) Schwingenschlogl, U.; Schuster, C.; Fresard, R.; Stripe segregation and magnetic coupling in the nickelate La-5/3Sr1/3NiO4 Ann. Phys.-Berlin 2009, 18, 107-113. (49) Gou, G. Y.; Grinberg, I.; Rappe, A. M.; Rondinelli, J. M.; Lattice normal modes and electronic properties of the correlated metal LaNiO3 Phys. Rev. B 2011, 84, 144101. (50) Punkkinen, M. P. J.; Kokko, K.; Vayrynen, I. J.; The electronic structure of K2NiF4 and K2CoF4: beyond LSDA Solid State Commun. 2001, 117, 583-588. (51) Rog, T.; Murzyn, K.; Hinsen, K.; Kneller, G. R.; nMoldyn: A program package for a neutron scattering oriented analysis of Molecular Dynamics simulations J. Comput. Chem. 2003, 24, 657-667.


29


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 30

(52) Parlinski, K., Calculation of phonon dispersion curves by the direct method, in: Neutrons and Numerical Methods-N(2)M; Amer Inst Physics: Melville, 1999; Vol. 479, p. 121-126. (53) Bates, F. E.; Eldridge, J. E.; Normal modes of tetragonal La2NiO4 and La2CuO4, isomorphs of the hight Tc superconductor La2-xSrxCuO4 Solid State Commun. 1989, 72, 187190. (54) Pintschovius; Bassat; Odier; Gervais; Chevrier; Reichardt; Gompf; Lattice dynamics of La2NiO4 Phys. Rev. B 1989, 40, 2229-2238.


30

Lattice Dynamics Modified by Excess Oxygen in Nd - American

Recommend Documents