Acceptor Doping and Oxygen Vacancy Migration in ... - ACS Publications

Article pubs.acs.org/JPCC

Acceptor Doping and Oxygen Vacancy Migration in Layered Perovskite NdBaInO4‑Based Mixed Conductors Xiaoyan Yang, Shuaibo Liu, Fengqi Lu, Jungu Xu, and Xiaojun Kuang* Guangxi Ministry-Province Jointly-Constructed Cultivation Base for State Key Laboratory of Processing for Nonferrous Metal and Featured Materials, Guangxi Universities Key Laboratory of Non-ferrous Metal Oxide Electronic Functional Materials and Devices, College of Materials Science and Engineering, Guilin University of Technology, Guilin 541004, PR China S Supporting Information *

ABSTRACT: The Ca2+ and Ba2+ solubility on Nd3+ sites in new layered perovskite NdBaInO4 mixed oxide ionic and hole conductor and their effect on the oxide ion conductivity of NdBaInO4 were investigated. Among the alkaline earth metal cations Ca2+, Sr2+, and Ba2+, Ca2+ was shown to be the optimum acceptor−dopant for Nd3+ in NdBaInO4 showing the largest substitution for Nd3+ up to 20% and leading to oxide ion conductivities ∼3 × 10−4−1.3 × 10−3 s/cm within 600−800 °C on Nd0.8Ca0.2BaInO3.9 composition, exceeding the mostconducting Nd0.9Sr0.1BaInO3.95 in the Sr-doped NdBaInO4. Energetics of defect formation and oxygen vacancy migration in NdBaInO4 were computed through the atomistic static-lattice simulation. The solution energies of Ca2+/Sr2+/Ba2+ on the Nd3+ site in NdBaInO4 for creating the oxygen vacancies confirm the predominance of Ca2+ on the substitution for Nd3+ and enhancement of the oxygen vacancy conductivity over the larger Sr2+ and Ba2+. The electronic defect formation energies indicate that the p-type conduction in a high partial oxygen pressure range of the NdBaInO4-based materials is from the oxidation reaction forming the holes centered on O atoms. Both the static lattice and molecular dynamic simulations indicate two-dimensional oxygen vacancy migration within the perovskite slab boundaries for the acceptor-doped NdBaInO4. Molecular dynamic simulations on the Ca-doped NdBaInO4 specify two major vacancy migration events, respectively, via one intraslab path along the b axis and one interslab path along the c axis. These paths are composed by two terminal oxygen sites within the perovskite slab boundaries.

■

INTRODUCTION

conduction in perovskite-related phases via controlling stoichiometry and doping defect chemistry. Among the perovskite-related materials, n = 1 RP A2BO4 layered perovskites containing valence-variable B cations recently received growing attention as alternative cathode materials for SOFCs because of their highly mixed electron and oxide ion conducting properties with particular interest in the oxygen hyperstoichiometric compositions showing interstitial oxide ion conductivity,6,13 although the oxygen vacancy conduction is also possible on the basis of theoretical modeling studies.13 The oxide ion migration is highly anisotropic in these layered perovskites owing to the intergrowth of the perovskite slabs and rock salt AO layers in the structures. Recently, a mixed oxide ionic and electronic conductor NdBaInO4 with a novel layered perovskite structure (Figure 1) was reported by Fujii et al.20 NdBaInO4 adopts a monoclinic structure containing alternative [NdO] and Nd1/4Ba3/4InO3 unit layers with the InO6 edge-facing Nd−O units, differing from the typical RP- and Dion−Jacobson21−23 (DJ)-type layered perovskites that contain apical oxygen-facing AO units. There are two

Oxide ion conducting materials have various important technological applications including electrolytes for solid oxide fuel cells (SOFCs)1−5 and oxygen sensors and pumps for the pure oxide ion conductors, cathodes for SOFCs,6 oxygen permeation membranes,7 gas conversion, and reformation catalyst8 for the mixed oxide ionic and electronic conductors. The trend of lowering the operating temperature for these various applications down to ∼500 °C has stimulated extensive search for new oxide ion conductors.2 The oxygenvacancy-conducting materials based on fluorite structure (e.g., yttrium-stabilized ZrO2 (YSZ),5 gadolinium-doped CeO2 (GDC)),9 perovskite or perovskite-related structures (e.g., Sr, Mg-doped LaGaO3 (LSGM),10,11 and Ruddlesden−Popper12 (RP)-layered perovskite La2−xSrxCoO4±δ)13 have attracted considerable attention. Although the structure types other than fluorite and perovskite with mobile oxygen interstitial defects received particular interest in exploring new oxide ion conductors,4,14−17 recently the ferroelectric Na0.5Bi0.5TiO3based oxide ion conductor has made perovskites again in the frontier of search for new oxide ion conductors.18,19 This new oxide ion conductor identified from ferroelectric oxides emphasizes the great potential on exploring oxide ion © XXXX American Chemical Society

Received: January 21, 2016 Revised: March 11, 2016

A

DOI: 10.1021/acs.jpcc.6b00700 J. Phys. Chem. C XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry C

migration in the layered perovskite structure of NdBaInO4 for the first time.

■

EXPERIMENTAL SECTION Synthesis. Polycrystalline samples of Nd1−xMxBaInO4−0.5x (M = Ca and Sr) and Nd1−xBa1+xInO4−0.5x (x = 0−0.5) were synthesized by conventional high-temperature solid-state reaction method. Nd2O3 (99.9%, Aladdin), In2O3 (99.99%, Aladdin), BaCO3 (99%, Aladdin), SrCO3 (99%, Aladdin), and CaCO3 (99%, Aladdin) were used as raw materials, which were weighed according to the correct stoichiometries and mixed thoroughly in ethanol in agate mortar. The mixed powders were pressed uniaxially into pellets with 12 mm diameter and ∼2 mm thickness and calcined at 1000 °C for 8 h in air with heating and cooling rates of 5 °C/min, then were reground and pressed into pellets again by a cold-isostatic pressing facility under pressure 250 MPa. The Ca-doped compositions were sintered at 1300 °C for 12 h, and the Sr- and Ba-doped samples were fired at 1400 °C for 12 h to get the ceramic pellets with ∼90−93% of X-ray theoretical density. Characterization. The phase formation in the samples were examined by powder X-ray diffraction (XRD) using a Panalytical X’Pert PRO diffractometer with a PIXcel 1D detector using Cu Kα radiation. The XRD data was analyzed by the Rietveld method,33 which was carried out using the TopasAcademic software.34 Impedance spectroscopy measurements were carried out with a Solartron 1260 frequency response analyzer over the 10−2−107 Hz frequency range within 300− 850 °C. Platinum paste was coated on the opposite faces of the pellets and fired at 800 °C for 40 min to burn out the organic components to form electrodes. The impedance data analysis was carried out using the Zview software. The oxygen transport number was determined by electromotive force (EMF) measurements on oxygen concentration cells35 of O2∥air and N2∥air at 700−850 °C. The pellets were attached on the alumina tube using glass sealant that was fired at 900 °C, and the gas-tightness was examined via using soapy water after cooling down to room temperature to ensure no apparent gas leakage prior to warming up again to high temperature for the EMF measurements. The theoretical EMF values of the oxygen concentration cells were calculated using the Nernst equation. The partial oxygen pressure (pO2) in the N2 gas was determined to be 10−4 atm by an YSZ sensor at 800 °C. The oxygen transport number is calculated from the ratio of experimental and theoretical EMF values. The ac conductivity as a function of pO2 was measured between 600 and 800 °C over a pO2 range of 10−24−1 atm, which was monitored by the YSZ sensor close to the sample. The pO2 was controlled using O2−N2 (within 1−10−4 atm) and 1%O2/N2−5%H2/N2 (within 10−12−10−24 atm) gas mixtures, for which the HORIBA mass flow controllers (S48 32/HMT) were used.

Figure 1. (a) [010] and (b) [001] projection of the NdBaInO4 layered perovskite structure. The blue, yellow, green, and red spheres stand for Nd, Ba, In, and O atoms, respectively.

bridging oxygen sites (O1 and O2) and two terminal oxygen sites (O3 and O4) in the two-layer perovskite slabs of NdBaInO4 structure (Figure 1). Within the perovskite slabs, O1 atoms bridge the one-dimensional (1D) octahedral chains parallel to the c axis (Figure 1a), which are linked by O2 atoms forming zigzag-type octahedral slabs (Figure 1b), whereas the terminal O3 and O4 atoms form octahedral-edge oxygen layers in the perovskite slab boundaries, similar to the A2B2O7-type layered perovskites, e.g., Sr2(Nb/Ta)2O7 containing 4-layer perovskite blocks.24,25 Interestingly, the parent material NdBaInO4 displayed mixed hole (p-type) and oxide ionic conduction, although all of the crystallographic sites for oxygen atoms were shown to be fully occupied. Sr2+ substitution for Nd3+ was shown to enhance the oxide ion conductivity through the oxygen vacancy conduction.26 The difference bond valence sum (DBVS) map of NdBaInO4 suggested two-dimensional (2D) oxide ion diffusion within the [NdO] layers involving the terminal O3 and O4 sites only within the perovskite block boundaries.20 The atomistic static lattice and molecular dynamic (MD) simulations based on the interatomic potential method are powerful computational tools on probing the energetics of oxygen defect formations and migration and elucidation of oxygen defect migration mechanisms, which had been successfully applied in many perovskite and perovskite-related materials,13,27−31 e.g., the LaGaO3-based oxide ion conductors30 and RP La2−xSrxCoO4±δ,13 as well as some other structural types, e.g., apatites3,16 and melilite32 with tetrahedral units. Such modeling study is helpful to understanding the chemical doping and ionic transport behaviors at atomic level and therefore may promote further development of oxide ion conductors. In this study, acceptor substitutions of Ca2+ and Ba2+ on the Nd3+ sites were carried out on the NdBaInO4 layered perovskite aiming for creating mobile oxygen vacancies, and the energetic of oxygen defect formations and oxygen vacancy migration were investigated using the atomistic static lattice and MD simulations to get an insight into the oxide ion

Table 1. Buckingham Interatomic Potential and Shell Model Parameters for the NdBaInO4-Based Materials interaction

A (eV)

ρ (Å)

C (eV Å6)

Y (e)

k (eV Å−2)

Nd −O Ba2+−O2−39 In3+−O2−29 O2−−O2−27 Ca2+−O2−40 Sr2+−O2−39

1597.1567 4818.416 1495.6 22764.3 1228.9 1956.39

0.3601 0.3067 0.331 0.149 0.3372 0.33685

0 0 4.325 43.0 0 19.22

0 1.831 −6.1 −2.239 1.26 1.831

0 34.05 1680.0 42.0 34.0 21.53

3+

2−

B


Article

The Journal of Physical Chemistry C Atomistic Modeling Method. Static Lattice Simulation. The atomistic static lattice simulations on defect formation in NdBaInO4 were carried out using the General Utility Lattice Program (GULP)36,37 on the basis of the interatomic potential approach.31 The Buckingham potential function38 was used to model interaction between ions with the shell model38 to describe the electronic polarizability for the structure modeling of NdBaInO4. The potential parameters used for the atomistic simulation are listed in Table 1, among which the parameters for Ba−O, In−O, and O−O were taken from the previous studies,27,29,39 and the Nd−O potential parameters was slightly modified through the relaxed fitting procedure implemented in the GULP package on the basis of the initial parameters from the previous publication of Lewis et al.40 for a better reproduction of crystal structure of NdBaInO4 via refining its A value with its C value fixed during the fitting. The extrinsic and intrinsic defect formation energies were then calculated based on appropriate combinations of vacancy, interstitial and dopant defect energy terms. The energy profiles for intraslab and interslab oxygen migration in NdBaInO4 were calculated, from which the energy barriers for the oxygen migration were derived. The formation energies of electronic defects (holes and x electrons) via, respectively, oxidation (V•• O + 0.5O2(g) → OO + • x •• 2h ) and reduction (OO → VO + 0.5O2(g) + 2e′) reactions were calculated via following the procedure, which was employed for the La2O3,41 Ba2In2O5,29 and LaBO3-type perovskites.28,30 The hole centers were modeled as O− or In4+ substitutionals, and electron centers were modeled as In2+ or In+ substitutionals. The energies for the oxidation and reduction equations are derived from the relevant defect energies and the intra-atomic energy terms, including the ionization energies of In (II, 18.81 eV; III, 28.03 eV; and IV, 54.4 eV),29 the electron affinity of O (I, −1.47 eV, and II, 8.75 eV), and the dissociation energy of an O2 molecule (5.16 eV).41 Molecular Dynamic Simulation. The oxygen vacancy migration was investigated by the interatomic-potential-based MD simulation on the Ca-doped NdBaInO4. The MD simulations were carried out with the DL_POLY code.42 The simulation box consisted of 5 × 8 × 6 unit cells, containing 6672 atoms and giving a composition of Nd0.9Ca0.1BaInO3.95. The Ca dopants and oxygen vacancies were distributed randomly within the simulation box. The systems were equilibrated first under a constant pressure of 1 atm at specific temperatures in 1000−1400 °C for 300 000 time steps with a time step of 0.2 fs before carrying out the main MD simulation for 300 ps with 1 500 000 time steps in the NVT ensemble (thermostatted to maintain a constant temperature T with constant number of particles N and constant volume of particles V). The Visual Molecular Dynamic (VMD) package43 was used to carry out MD data analysis, and the mean square displacements (MSDs) were calculated with the nMoldyn code.44 Oxygen diffusion coefficients are calculated from the slope of the MSD plots as a function of simulation time.

Figure 2. XRD patterns of (a) Nd1−xCaxBaInO4−0.5x and (b) Nd1−xBa1+xInO4−0.5x. The insets enlarge the plot within 28−32° to show the reflections from the Ba2In2O5-like secondary phase (marked with ∇).

was seen in the x = 0.5 sample. The refined cell volumes for the NdBaInO4 phase within the single-phase region (x = 0−0.2) of Nd1−xCaxBaInO4−0.5x displays contraction with the Ca content (Table 2). For the Ba2+ substitution for Nd3+ in NdBaInO4, single-phase samples were obtained in a narrower region x ≤ 0.1 for Nd1−xBa1+xInO4−0.5x than that for the Ca-doped compositions (Figure 2b). Similar to the Ca-doping on the Nd sites, increasing Ba/Nd ratio to higher values (x = 0.15− 0.5) resulted in Ba2In2O5-like phase as the secondary phase, which became the main phase at x = 0.4−0.5 compositions (Figure 2b). For comparison with the Ca- and Ba-doped compositions, the Nd1−xSrxBaInO4−0.5x solid solution formation was re-examined here. Similar to Nd1−xBa1+xInO4−0.5x, our data indicates that single phase was obtained in the x ≤ 0.10 range in Nd1−xSrxBaInO4−0.5x (Figure S1): the Ba2In2O5-like secondary phase appeared in the compositions x = 0.15−0.3. Both Nd1−xBa1+xInO4−0.5x and Nd1−xSrxBaInO4−0.5x display cellvolume expansion with the x (Table 2), consistent with the Ba2+ or Sr2+ substitution for the smaller Nd3+.45 Ionic Conductivity. The complex impedance data of the parent material NdBaInO4 pellet (∼91% relative density) at 350 °C comprises one large semicircular arc and a small tail (Figure 3a). The large semicircular arc can be modeled with an equivalent circuit consisting of parallel R and C: The lowfrequency intercept of the arc was extracted as R, and the associated C estimated by 2πf maxRC = 1 is ∼3 pF/cm, indicative of the bulk response, where f max is the frequency in hertz at the arc maximum.46 The small tail in the low-frequency region has capacitance with magnitude of 10−11−10−10 F/cm, suggesting the grain boundary response.46 No apparent electrode response

■

RESULTS AND DISCUSSION Nd1−xMxBaInO4−0.5x (M = Ca and Ba) Solid Solution. The XRD data of Ca- and Ba-doped samples Nd1−xCaxBaInO4−0.5x and Nd1−xBa1+xInO4−0.5x are shown in Figure 2. For Ca-doped materials (Figure 2a), single-phase materials were achieved on compositions x = 0−0.2. Apparently, Ba2In2O5-like impurity phase was observed in the compositions x = 0.3−0.5, and a small amount of CaO phase C


Article

The Journal of Physical Chemistry C Table 2. Refined Cell Parameters of Nd1−xCaxBaInO4‑0.5x, Nd1−xSrxBaInO4‑0.5x, and Nd1−xBa1+xInO4‑0.5x composition

a(Å)

b(Å)

c(Å)

β(deg)

V(Å3)

NdBaInO4 Nd0.95Ca0.05BaInO3.975 Nd0.9Ca0.1BaInO3.95 Nd0.85Ca0.15BaInO3.925 Nd0.8Ca0.2BaInO3.9 Nd0.95Sr0.05BaInO3.975 Nd0.9Sr0.1BaInO3.95 Nd0.95Ba1.05InO3.975 Nd0.9Ba1.1InO3.95

9.0910(2) 9.0990(1) 9.1022 (1) 9.0967 (2) 9.0869(2) 9.1001(1) 9.1029(1) 9.1035(3) 9.1113(9)

6.0475(7) 6.0428(1) 6.0342(1) 6.0361(1) 6.0273(8) 6.0479(2) 6.0453(1) 6.0521(2) 6.0484(2)

8.2636(8) 8.2590(1) 8.2647(1) 8.2593(1) 8.2539(9) 8.2630(1) 8.2689(7) 8.2639(2) 8.2706(6)

103.423(8) 103.385(1) 103.391(1) 103.367(1) 103.327(1) 103.397(7) 103.384(4) 103.417(2) 103.405(4)

441.91(4) 441.77(1) 441.60(1) 441.22 (1) 439.89(9) 442.39(1) 442.68(1) 442.88(2) 443.37(4)

composition here, which was reported as the most conducting material in the Sr-doped NdBaInO4 by Fujii et al.26 The Nd0.9Sr0.1BaInO3.95 ceramic (∼90% relative density) showed apparent electrode response arc from the ionic conduction (Figure S2b) at low temperature below 400 °C in addition to the bulk and grain boundary responses. To confirm whether the ionic conduction behavior arises from the oxide anions in the alkaline earth cationic acceptordoped NdBaInO4 materials, impedance measurements under O2 and N2 atmospheres and EMF measurements of oxygen concentration cells were carried out on Ca-doped compositions as well as the parent material NdBaInO4. Both parent and Cadoped NdBaInO4 displayed enhanced resistivities when the atmosphere was changed from O2 to N2, agreeing with the ptype conduction identified in the previous studies of Fujii et al.20,26 For the Ca-doped compositions, when the gas was changed from O2 to low-pO2 N2 atmosphere, the electrode response changed from a semicircular arc into an inclined spike (inset of Figure 4a), in addition to the emergence of a small arc from the grain boundary response because of the enhanced resistivity under low-pO2 N2 environment. This is consistent with the enhanced polarization resistance associated with the charge transfer reaction O2 + 2e ↔ O2− along the interface between the sample and electrode in low-pO2 N2 environment,46 thus suggesting that the ionic conduction is from oxide ions in the Ca-doped compositions. Similar behavior of electrode response arc with pO2 is commonly observed in the oxide ion conductors, for example, Na0.5Bi0.5TiO3-based19 and NaBi3V2O1047 materials, and is used for diagnosis for the oxide ion conduction,19,47,48 although because there is little electrode response in the impedance data of undoped NdBaInO4 the atmosphere change from O2 to N2 was found to have little effect on the shape of complex impedance plot for the parent NdBaInO4 (Figure 4b) except for the reduction on the bulk and total conductivity, indicating that the oxide ionic conduction in the parent material is limited. The EMF measurements for the parent material (Table S1) on the O2∥air and N2∥air cells gave low values within 6 mV and low oxygen transport numbers of σ(Nd 0.9 Sr 0.1 BaInO 3.95 ) > σ(Nd 0.9 Ba 1.1 InO 3.95 ). At 500 °C, the Nd 0.9 Sr 0.1 BaInO 3.95 composition has conductivity ∼3.0 × 10−4 s/cm that is comparable to the dc conductivity (solid red line in Figure 6c) of the Nd0.9Sr0.1BaInO3.95 pellet with comparable density reported by Fujii et al. 26 and is between those for Nd0.9Ca0.1BaInO3.95 and Nd0.9Ba1.1InO3.95. The acceptor-substitutions of Ca and Sr apparently reduced the activation energy E a ≈ 0.95 eV of NdBaInO 4 to 0.73−0.77 eV for Nd0.9Ca0.1BaInO3.95 and Nd0.9Sr0.1BaInO3.95. However, in the Nd0.9Ba1.1InO3.95 composition, the activation energy is similar to that for the undoped NdBaInO4. In terms of the conductivity comparison of Ca/Sr/Ba-doped compositions (Figures 5 and 6c), the Ca2+ appears as the optimal dopant on the Nd3+ site on improving the oxide ion conductivity of NdBaInO4 among Ca2+, Sr2+ and Ba2+. Energetic of Defect Formation. The interatomic potential parameters listed in Table 1 reproduced well the crystal structure of NdBaInO4. The lattice parameters were reproduced within 0.05 Å, the bond lengths within 0.2 Å, and the mean bond lengths within 0.03 Å (Table S2): Most In−O bond lengths in InO6 octahedron were reproduced within ∼0.06 Å with one exception of slightly large deviation at ∼0.1 Å. No additional experimental physical property data is available on this new compound NdBaInO4 for further

Figure 4. Complex impedance plots of (a) Nd0.8Ca0.2BaInO3.95 and (b) NdBaInO4 at 800 °C in O2 flow in comparison with those in N2 flow in the inset for each plot. Rb and Rt denote bulk and total resistivities, respectively. The numbers denote the logarithm values of the selected frequencies marked by filled circles.

Figure 5. pO2-dependency of total conductivity for Nd0.8Ca0.2BaInO3.9 at 700 and 800 °C. The inset shows the Arrhenius plot of oxide ionic conductivity of Nd0.8Ca0.2BaInO3.9 (Ca0.2) within 600−800 °C compared with that for Nd0.8Sr0.1BaInO3.95 (Sr0.1) (represented by the red line) from Fujii et al.,26 where the activation energies are marked.

dependency of total conductivity of Nd0.8Ca0.2BaInO3.9 at 700 and 800 °C, displaying mixed ionic and electronic conduction, similar to the conductivity behavior to pO2 for NdBaInO4 and Sr-doped NdBaInO4.20,26 In the high-pO2 range from 10−4 atm to 1 atm, the conductivity increased with the pO2 and was essentially constant below 10−8 atm. Such pO2-dependent conductivity is described as σt = σi + A(pO2)n, where the first component σi denotes the pO2-independent oxide ionic E


Article


the dopants and host cations: The size of Ca2+ is close to Nd3+, and Ba2+ is significantly larger than Nd3+. However, the size difference between Sr2+ and Nd3+ is in the intermediate place;45 the replacement of Nd3+ by the cations with the most comparable size may minimize local structural relaxation, thus gaining the highest solubility. The conductivities of Nd0.9Ca0.1BaInO3.95, Nd0.9Sr0.1BaInO3.95, and Nd0.9Ba1.1InO3.95 (Figure 6) also demonstrate a proportional link with the ease of Ca/Sr/Ba substitution for Nd in NdBaInO4. The elastic strain effect was considered here for such behavior: When the size mismatch between the host and dopant is the smallest, the minimal binding energy for the dopant-vacancy cluster is expected, which is beneficial to the ionic conductivity.49,50 However, the calculated binding energies (Table 3) of the dopant-vacancy clusters in Ca-, Sr-, and Ba-doped NdBaInO4 are comparable ca. −0.9 eV, indicating that trapping for the migrating oxygen vacancies in NdBaInO4 from the Ca, Sr, and Ba dopants could be comparable. Therefore, the conductivity behavior of Ca-/Sr-/Ba-doped NdBaInO4 to the dopant sizes could be interpreted by the structural relaxation arising from the size mismatch between the Nd host and dopants: The significant structural relaxation/distortion from the replacement of Nd3+ with the large Ba2+ cations could be detrimental to the oxygen migration. The energy difference among the vacancies on O1, O2, O3, and O4 sites vary within ∼0.3 eV, showing no strong site preference for the oxygen vacancies in the layer perovskite structure of NdBaInO4. This is consistent with the refinement results from neutron powder diffraction data of Srdoped NdBaInO4 reported by Fujii et al.26 Although all oxygen sites in the parent material appear fully occupied, the pO2 dependency of conductivity measurement by Fujii et al. showed that the parent material possessed low-level oxide ion conductivity (∼3 × 10−5 s/cm at 850 °C) within intermediate pO2 range of ∼10−5−10−19 atm.20 This implies plausible formation of small amount of intrinsic oxygen defects in the parent material. However, the magnitudes of the formation energies for the intrinsic Frenkel and Schottky defects in NdBaInO4 (Table 3) indicate that the intrinsic defects are minor defects in the materials. Therefore, the lowlevel oxide ion conductivity may be rationalized as follows: If there was inadvertent or uncontrollable nonstoichiometry of Ba:Nd with slightly excess Ba in the parent material, then given the solution energy (1.6 eV) of Ba2+ on Nd3+ site, the Ba2+ substitution for Nd3+ could talk place during the preparation to introduce minor oxygen vacancy defects therefore result in the low-level oxide ion conduction, as revealed by the enhanced conductivity from the Ba 2+ -substitution for Nd 3+ in Nd1−xBa1+xInO4−0.5x described above in the Ionic Conductivity section. The calculated energies for the oxidation and reduction equations to create respectively holes and electrons (Table 3) show that the oxidation reaction to create the holes centered on O atoms is more favorable than the other oxidation−reduction reactions to produce hole centered on In atoms and electrons (In2+ and In−). This accounts for the fact that NdBaInO4-based materials displayed p-type conduction in the high-pO2 range whereas the n-type conduction appears in the extremely lowpO2 range.20,26 Additionally the formation energies of electrons indicate that the formation of In+ is more energy-favorable than that of In2+, consistent with the observation on the Ba2In2O5.29 Oxygen Vacancy Migration. It is well-known that oxygen vacancy migration in the perovskite octahedral network is via curved octahedral edge O−O paths through the saddle points

Figure 6. Arrhenius plots of the conductivities in air of (a) Nd1−xCaxBaInO4−0.5x and (b) Nd1−xBa1+xInO4−0.5x ceramics. (c) Comparison of the bulk conductivities in air of NdBaInO4, Nd 0.9 Ca 0.1 BaInO 3.95 (Ca 0.1 ), Nd 0.9 Ba 1.1 InO 3.9 (Ba 0 .1 ), and Nd0.9Sr0.1BaInO3.95 (Sr0.1) samples in 300−600 °C. The red solid line represents the dc conductivity data of the Nd0.9Sr0.1BaInO3.95 pellet from Fujii et al.26

validation of these potential parameters. The calculated solution energies (eV) of Ca2+ (0.76), Sr2+ (0.84), and Ba2+ (1.6) on Nd3+ sites show plausibility of creating oxygen vacancies in NdBaInO4: Ca2+ is the most favorable dopant on the Nd3+ sites among these three dopants, and the replacing of Nd3+ by Ba2+ is the most energy-unfavorable in NdBaInO4, roughly consistent with the solubility from the experimental investigation. This can be rationalized by the size difference between F


Article

The Journal of Physical Chemistry C Table 3. Formation Energies of Extrinsic and Intrinsic Defects in NdBaInO4 defect type acceptor doping

equation

energy (eV)

2CaO + OOx + 2NdxNd → 2Ca′Nd + V •• O + Nd 2O3

2SrO +

acceptor doping

2BaO +

OOx

dopant-vacancy cluster

•• Ca′Nd + V •• O → (Ca′NdV O )

−0.90


•• Sr′Nd + V •• O → (Sr′NdV O )

−0.88

acceptor doping

V •• O

+

2NdxNd

+

2NdxNd

0.76

OOx

→ 2Sr′Nd +

V •• O

→ 2Ba′Nd +

+ Nd 2O3

V •• O

+ Nd 2O3

(Ba′NdV •• O)

0.84 1.6

−0.88


Ba′Nd +

O Frenkel

OOx

Nd Frenkel

NdxNd → V‴Nd + Nd••• i

18

Ba Frenkel

x Ba Ba → V″Ba + Ba•• i

16

In Frenkel

x In In

→ V‴In +

In••• i

20

Ba−O Schottky

OOx

x Ba Ba

V •• O

Nd−O Schottky

OOx + 2/3NdxNd → V •• O + 2/3V‴ Nd + 1/3Nd 2O3

5.1

In−O Schottky

x OOx + 2/3In In → V •• O + 2/3V‴ In + 1/3In 2O3

7.4

full Schottky

OOx

→

+

+

V •• O

→

+ O″i

→

1/4NdxNd

5.5

+

+ V″Ba + BaO

x 1/4Ba Ba

+

x 1/4In In

8.1

V •• O+

→

1/4V‴Nd + 1/4V″Ba + 1/4V‴In + 1/4NdBaInO4

6.8

hole

x • − 0.5V •• O + 0.25O2 (g) → 0.5OO + h (O )

1.2

hole

x • 4+ 0.5V •• O + 0.25O2 (g) → 0.5OO + h (In )

9.9

electron

0.5OOx

5.1

electron

0.5OOx

→

0.5V •• O

→

0.5V •• O

2+

+ 0.25O2 (g) + e′(In ) +

+ 0.25O2 (g) + e′(0.5In )

4.8

energy-forbidden. However, the long-range sinusoidal-like migration path consisting of alternative interoctahedral O3− O4 (paths l) and octahedral edge O3−O4 (paths e) paths is also another possible intraslab diffusion path but has less probability given the higher energy barrier (∼0.82 eV for path 1) compared with the most two energy-favorable long-range intraslab migration paths with energy barriers ∼0.5−0.6 eV described above. The paths via the bridging O2 sites in the middle positions of two-layer perovskite blocks along the layerstacking direction (i.e., a axis) have higher energy barriers above 1.2 eV indicating that the migration along the remaining a axis to form 3D diffusion has much less probability because of the short-circuiting by the other diffusion paths along b and c axes with lower energy barriers, in consistence with the results of Fujii et al.20,26 Therefore, the oxygen vacancy migration in NdBaInO4 is 2D conduction preferably along both b and c axes involving two terminal (O3 and O4) and one bridging (O1) oxygen sites within the perovskite block boundaries. The magnitude of calculated energy barriers (0.52−0.82 eV) for these diffusion paths along b and c axes are close to the experimental activation energies 0.70−0.795 eV (Figure 5) of the oxide ion conduction for the Nd0.8Ca0.2BaInO3.9 and Nd0.9Sr0.1BaInO3.95.26 Regarding the oxygen vacancy migration between the perovskite slabs, the calculation showed that linear interslab O4−O4, O3−O3, and O3−O4 paths (paths k, j, and i, respectively in Figure 7b) have energy barriers (eV) of ∼0.61, 1.1, and 0.95, respectively. No curved paths with the lower energy barriers were obtained for O4−O4 and O3−O3 paths, whereas a curved O3−O4 path with energy barriers ∼0.85 eV lower than the linear path was obtained (Figure S3). These energy barriers indicate the ease of interslab vacancy migration along the O4−O4 path and probability of migration along the

instead of the linear path between the octahedral-edge oxygen sites.13,30,51 Here the oxygen migration energy profiles in NdBaInO4 were calculated along seven curved octahedral edge O−O paths (Figure 7a) and six interoctahedral O−O paths, including three intraslab paths and three interslab paths (Figure 7a,b) were also considered during the calculation, for which the energy barriers for both the linear and curved paths were calculated. The lowest energy barriers derived from the energy profiles along these O−O paths are listed in Table 4, which reveals the two most energy-favorable intraslab migration paths with energy barriers ∼0.5−0.6 eV composed of the octahedral edge O1−O4 (path d) and O3−O4 (path e) and interoctahedral O3−O4 (path h, intraslab) for the oxygen vacancies in the acceptor-doped NdBaInO4 (Figure S3). One is via the alternative octahedral edge and interoctahedral curved O3−O4 paths parallel to the b axis within the [NdO] layers in the perovskite block boundaries (Figure 7a,c), which is consistent with the 2D oxide ion diffusion within [NdO] layers proposed by Fujii et al. from the DBVS mapping.20 The other one is the sinusoidal-like octahedral edge O1−O4 path along the c axis (Figure 7b,d). Although the latter path was not shown in the DBVS mapping of NdBaInO4,20 that is a typical octahedral edge path for oxygen vacancy migration commonly observed in perovskite-related materials.13 These two intraslab paths permit formation of the long-range vacancy migrations along the b axis (the former) and c axis (the latter), respectively. The energy barriers of migration along interoctahedral O3− O4 paths within the perovskite slab with large separations ∼3.7 and ∼4.6 Å along the c axis, respectively labeled as paths l and m in Figure 7b, were also examined and found to have energy barriers of ∼0.82 eV (for path l) and ∼2.5 eV for (path m). Therefore, the long-range oxide ion migration along alternative paths l and m parallel to c axis within the perovskite slabs is G


Article


Figure 7. Oxygen migration paths: a (O1−O2), b (O2−O2), c (O2−O4), d (O1−O4), e (O3−O4), f (O1−O3), and g (O2−O3) denote the octahedral edge O−O paths; h (intraslab O3−O4), i (interslab O3−O4), j (interslab O3−O3), k (interslab O4−O4), l (intraslab O3−O4), and m (intraslab O3−O4) denote the interoctahedral O−O paths. Paths a−h are shown in panel a, and i−m are shown in panel b. The long-range migration paths parallel to b axis in one [NdO] layer consisting of alternative edge O4−O3 (path e) and interoctahedral O3−O4 (intraslab path h) paths that are linked by the interoctahedral O3−O4 path in cyan (intraslab path l) along c axis are shown in panels a and c. In panel c, the neighboring octahedral layer bridged by the O2 sites is omitted for clarity. The sinusoidal-like alternative O1−O4 paths along the c axis that are linked by the short-range interslab O4−O4 (path k) and O3−O4 (path i) paths are shown in panels b and d. The small spheres in dark gray denote the pathways with energy barriers ∼0.52−0.60 eV and those in cyan represent the pathways with energy barriers ∼0.82−0.85 eV for the oxygen vacancy migration.

curved O3−O4 path. However, the high-energy barrier (∼1.1 eV) of the interslab O3−O3 path could prevent from formation of the long-range nonlinear interslab migration path (O4−O4− O3−O3) along the c axis (i.e., the alternative paths k, i, and j in Figure 7b). To complement the oxygen vacancy migration paths from the static lattice simulation, molecular dynamic simulations were carried out on composition Nd0.9Ca0.1BaInO3.95, which directly provided more mechanistic details of oxygen vacancy migration in the acceptor-doped NdBaInO4. Figure 8 shows scatter plots of ion positions from the MD simulation of Nd0.9Ca0.1BaInO3.95 at 1400 °C, where oxygen atoms originally on the crystallographically distinct sites (O1−O4) are marked with different colors. The streaming and overlapping of colors indicates that oxide ion migration takes place among the O1, O3, and O4 sites, whereas the isolated color for O2 sites shows that O2 sites are seldom involved in the oxygen migration. Therefore, consistent with the static lattice simulation, the MD simulations confirmed that the oxygen vacancy migration is two-dimensional within the perovskite-slab boundary region,

Table 4. Energy Barriers (ΔE) for Oxygen Vacancy Migration along O−O paths Labeled in Figure 7 path

O−O separation (Å)

Octahedral Edge Path 2.993 3.054 3.209 2.998 2.85 2.994 3.310 Interoctahedral Path h (intraslab O3−O4) 3.289 i (interslab O3−O4) 3.233 j (interslab O3−O3) 3.144 k (interslab O4−O4) 3.038 l (intraslab O3−O4) 3.741 m (intraslab O3−O4) 4.557 a (O1−O2) b (O2−O2) c (O2−O4) d (O1−O4) e (O3−O4) f (O1−O3) g (O2−O3)

ΔE (eV) 1.20 1.06 1.19 0.52 0.47 1.27 1.66 0.60 0.85 1.08 0.54 0.82 2.47

H


Article


the short-range migration revealed by the static lattice simulation. Apart from these two major diffusion paths associated with the terminal O3 and O4 sites within the perovskite-slab boundary, the MD simulation showed indeed the intraslab migration between the bridging O1 and terminal O4(O3) sites (Figure 8a,b). However, it appears a much less frequent migration event in the MD simulation, in contrast with the static lattice simulation that overestimated the ease of vacancy migration along the intraoctahedral O1−O4 paths with low energy barrier (∼0.52 eV). Figure 9 shows the calculated MSD values of Ca, Nd, Ba, In, and O atoms. As expected from the scatter plots described

Figure 9. MSD values of Ca, Nd, Ba, In, and O atoms as a function of time from the MD simulation at 1400 °C for Nd0.9Ca0.1BaInO3.95. The inset enlarges the MSD values of Nd, Ba, In, and Ca cations.

above, the MSD data shows that the metal cations vibrate around their lattice positions, and O2 atoms are nearly immobile given the essentially constant MSD values over the simulation time whereas O1, O3, and O4 atoms participate the migration events. The moving speeds of O1, O3, and O4 atoms demonstrate an order of O4 > O3 > O1, consistent with the static lattice simulation showing that the migration paths via O4 sites are the most energy-favorable. The MSD values of O1, O3, and O4 were used to calculate the oxygen diffusion coefficients, which is in the range of 10−6−10−7 cm2/s (Figure S4) although there are no experimental values available for direct comparison. The activation energies from the oxygen diffusion coefficients is 0.53 eV, which is in agreement with the lowest migration energy barriers (0.5−0.6 eV) from the static lattice simulation but lower than the experimental values of 0.70− 0.795 eV in the Ca- and Sr-doped26 NdBaInO4 from the conductivity measurements as a function of pO2 at 600−800 °C. However, the diffusion coefficients calculated using the MSD values of the fastest O4 specie only gave activation energy 0.75 eV, which has an excellent agreement with the experimental values. Finally, the oxygen vacancy migration paths identified in the NdBaInO4 layered perovskite are compared with the other layered perovskites focusing on the RP phases only owing to lack of oxygen vacancy migration mechanistic investigation on the DJ layered phases to the best of our knowledge. The intraslab and interslab vacancy migration paths in NdBaInO4 are similar to those in oxygen vacancy conducting n = 1 RP La2−xSrxCoO4−0.5x, in which the intraslab migration is more favorable than the interslab migration.13 With an increase of octahedral layer number of the perovskite slabs in RP phase, the intraslab migration was shown to be a predominant event over the interslab migration in the n = 2 and 3 RP phases,52,53

Figure 8. Scatter plots of ion positions from the MD simulation of Nd0.9Ca0.1BaInO3.95 at 1400 °C viewed down (a) c axis and (b) b axis. (c) Enlargement of the plot of two neighboring O3−O4 edge layers in the perovskite-slab boundary viewed down along the a axis to show the interslab and intraslab migration marked by black and red dashed lines, respectively. Green, orange, blue, red, and purple dots represent ions originally on O1, O2, O3, O4, and In sites, respectively. The large cations Ca, Nd, and Ba are omitted for clarity.

showing the two frequent migration events taking place along intraslab (Figure 8a) and interslab (Figure 8b) paths, respectively, parallel to the b and c axes that are composed of O3 and O4 sites. The intraslab migration path along the b axis consists of alternative edge O4−O3 and interoctahedral O3− O4 routes within the [NdO] layers, in accordance with the static lattice simulation. As revealed by the scatter plot of two neighboring O3−O4 edge layers in the perovskite-slab boundary that is enlarged in Figure 8c, the interslab vacancy migration along the c axis takes place along not only O4−O4 and O3−O4 paths but also the O3−O3 path, which was shown to possess an energy barrier (∼1.1 eV) larger than those for O4−O4 (∼0.54 eV) and O3−O4 (0.85 eV) paths by the static lattice simulation. Thus, the MD simulation implies that the long-range sinusoidal-like path along the c axis (Figure 8c) is highly plausible for the interslab vacancy migration, instead of I


Article

The Journal of Physical Chemistry C in which the inner bridging oxygen sites within the perovskite slabs are involved more frequently. However, within the twolayer perovskite slabs in NdBaInO4, both intraslab and interslab migrations involving the terminal oxygen sites within the perovskite-slab boundary have comparable contributions to the vacancy conduction.

■

■

CONCLUSIONS The present study combining the experimental investigation and atomistic modeling gets deep insight into the 2D oxygen vacancy conduction in new layered perovskite NdBaInO4-based mixed conductor. The following major points can be drawn from the results. (1) Ca2+ is the most favorable acceptor− dopant among the alkaline earth metal cations Ca2+, Sr2+, and Ba2+ for Nd3+ in the layered perovskite NdBaInO4 therefore has predominate enhancement on the oxygen vacancy conduction of NdBaInO4 over the larger Sr2+ and Ba2+. EMF and conductivity versus pO2 measurements confirmed the enhancement of oxide ion conduction in NdBaInO4 upon the Ca doping. Oxide ionic conductivity ∼3 × 10−4−1.3 × 10−3 s/cm within 600−800 °C was achieved on Nd0.8Ca0.2BaInO3.9 composition with activation energy ∼0.70 eV. (2) The static lattice simulation showed that Ca2+ has the lowest solution energy of on Nd3+ sites in NdBaInO4 for creating oxygen vacancy defects among Ca2+, Sr2+, and Ba2+, confirming the predominance of Ca2+ on the substitution for Nd3+ and enhancement of the oxide ion conductivity over the larger Sr2+ and Ba2+. The electronic defect formation energies indicate that the p-type conduction in high-pO2 range for NdBaInO4-based materials is from the oxidation reaction forming the holes centered on O atoms. The solution energy of Ba2+ on Nd3+ site and formation energies of extrinsic defects in the parent NdBaInO4 as well as enhancement of oxide ion conductivity with the Ba2+ substitution for Nd3+ in Nd1−xBa1+xInO4−0.5x indicate that the low-level oxide ion conduction in undoped NdBaInO4 could result from the inadvertent or uncontrollable acceptor-doping of Ba2+ on Nd3+ sites. (3) Both the static lattice and molecular dynamic simulations indicate 2D oxygen vacancy migration in acceptor-doped layered perovskite NdBaInO4 where the bridging O1 and the terminal O3 and O4 sites are involved in, whereas the migration along the a axis across the O2 bridging sites is not practical. Molecular dynamic simulations specify two most-energy-favorable vacancy migration paths consisting of one intraslab path along the b axis and one interslab path along the c axis in Ca-doped NdBaInO4. These paths are composed by O3 and O4 sites within the perovskite-slab boundaries, whereas the migration along the paths via O1 site takes place much less frequently. The mechanistic details on the oxide ionic conduction revealed in this study on the new layered perovskite NdBaInO4 could have general significance to the similar layered perovskite (e.g., A2B2O7-type) containing terminal O−O edges and also contribute to understanding the oxygen vacancy migration in more widely RP and DJ layered perovskites.

■

concentration cells and oxygen transport numbers of Nd0.8Ca0.2BaInO3.9 and NdBaInO4; calculated and experimental structural parameters for NdBaInO4; energy profiles for the selected intraslab and interslab oxygen vacancy migration paths; Arrhenius plots of the calculated oxygen diffusion coefficients. (PDF)

AUTHOR INFORMATION

Corresponding Author

*Fax: +86 773 5896670. Tel.: +86 773 5896670. E-mail: [email protected]. Author Contributions

X. Y. and S. L. have contributed equally to this work. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS National Natural Science Foundation of China (No. 21101174), Guangxi Natural Science Foundation (No. 2014GXNSFGA118004), the Research Project (No. 213030A) of Chinese Ministry of Education, Program for New Century Excellent Talents in University (No. NCET-130752), Guangxi University Program for Hundred Talents for Returned Scholars, and Guangxi Ministry-Province JointlyConstructed Cultivation Base for State Key Laboratory of Processing for non-Ferrous Metal and Featured Materials (No. 13AA-8) are acknowledged for the financial support. We sincerely thank Prof. M. Saiful Islam, Dr. Alex Whiteside, and Dr. Chris Eames in the University of Bath (United Kingdom) for their assistance on the static lattice and molecular simulation. National Supercomputer Center in Guangzhou is acknowledged for the access to the computational facility.

■

REFERENCES

(1) Lashtabeg, A.; Skinner, S. J. Solid Oxide Fuel Cells - A Challenge for Materials Chemists? J. Mater. Chem. 2006, 16, 3161−3170. (2) Steele, B. C.; Heinzel, A. Materials for Fuel-Cell Technologies. Nature 2001, 414, 345−352. (3) Malavasi, L.; Fisher, C. A. J.; Islam, M. S. Oxide-Ion and Proton Conducting Electrolyte Materials for Clean Energy Applications: Structural and Mechanistic Features. Chem. Soc. Rev. 2010, 39, 4370− 4387. (4) Orera, A.; Slater, P. R. New Chemical Systems for Solid Oxide Fuel Cells. Chem. Mater. 2010, 22, 675−690. (5) Boivin, J. C.; Mairesse, G. Recent Material Developments in Fast Oxide Ion Conductors. Chem. Mater. 1998, 10, 2870−2888. (6) Chen, Y.; Téllez, H.; Burriel, M.; Yang, F.; Tsvetkov, N.; Cai, Z.; McComb, D. W.; Kilner, J. A.; Yildiz, B. Segregated Chemistry and Structure on (001) and (100) Surfaces of (La1−xSrx)2CoO4 Override the Crystal Anisotropy in Oxygen Exchange Kinetics. Chem. Mater. 2015, 27, 5436−5450. (7) Wang, H. H.; Tablet, C.; Feldhoff, A.; Caro, J. A Cobalt-Free Oxygen-Permeable Membrane Based on the Perovskite-Type Oxide Ba0.5Sr0.5Zn0.2Fe0.8O3‑δ. Adv. Mater. 2005, 17, 1785−1788. (8) Bouwmeester, H. J. M. Dense Ceramic Membranes for Methane Conversion. Catal. Today 2003, 82, 141−150. (9) Huang, K. Q.; Feng, M.; Goodenough, J. B. Synthesis and Electrical Properties of Dense Ce0.9Gd0.1O1.95 Ceramics. J. Am. Ceram. Soc. 1998, 81, 357−362. (10) Ishihara, T.; Matsuda, H.; Takita, Y. Doped LaGaO3 Perovskite Type Oxide as A New Oxide Ionic Conductor. J. Am. Chem. Soc. 1994, 116, 3801−3803. (11) Feng, M.; Goodenough, J. B. A Superior Oxide-Ion Electrolyte. Eur. J. Solid State Inorg. Chem. 1994, 31, 663−672.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.6b00700. XRD patterns of Nd1−xSrxBaInO4−0.5x; complex impedance spectra of Nd0.9Sr0.1BaInO3.95 and Nd0.9Ba1.1InO3.95 ceramics; EMF values of oxygen J


Article


(34) Coelho, A. A. TOPAS Academic V4; Coelho Software: Brisbane, Queensland, Australia, 2005. (35) Jing, X. P.; Rwest, A. AC Impedance and Gas Concentration Cell Measurements for Ba12Y4.67Ti8O35. Acta Phys.-Chim. Sin. 2002, 18, 617−623. (36) Gale, J. D. GULP: A Computer Program for the SymmetryAdapted Simulation of Solids. J. Chem. Soc., Faraday Trans. 1997, 93, 629−637. (37) Gale, J. D.; Rohl, A. L. The General Utility Lattice Program (GULP). Mol. Simul. 2003, 29, 291−341. (38) Dick, B.; Overhauser, A. Theory of the Dielectric Constants of Alkali Halide Crystals. Phys. Rev. 1958, 112, 90−103. (39) Bush, T. S.; Gale, J. D.; Catlow, C. R. A.; Battle, P. D. SelfConsistent Interatomic Potentials for the Simulation of Binary and Ternary Oxides. J. Mater. Chem. 1994, 4, 831−837. (40) Lewis, G.; Catlow, C. Potential Models for Ionic Oxides. J. Phys. C: Solid State Phys. 1985, 18, 1149. (41) Ilett, D. J.; Islam, M. S. Role of Structural Defects and Oxygen Ion Migration in the Catalytic Activity of La2O3. J. Chem. Soc., Faraday Trans. 1993, 89, 3833−3839. (42) Todorov, I. T.; Smith, W.; Trachenko, K.; Dove, M. T. DL_POLY_3: New Dimensions in Molecular Dynamics Simulations via Massive Parallelism. J. Mater. Chem. 2006, 16, 1911−1918. (43) Humphrey, W.; Dalke, A.; Schulten, K. VMD: Visual Molecular Dynamics. J. Mol. Graphics 1996, 14, 33−38. (44) 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. (45) Shannon, R. Revised Effective Ionic Radii and Systematic Studies of Interatomic Distances in Halides and Chalcogenides. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976, 32, 751−767. (46) Irvine, J. T. S.; Sinclair, D. C.; West, A. R. Electroceramics: Characterization by Impedance Spectroscopy. Adv. Mater. 1990, 2, 132−138. (47) Sinclair, D. C.; Watson, C. J.; Howie, R. A.; Skakle, J. M. S.; Coats, A. M.; Kirk, C. A.; Lachowski, E. E.; Marr, J. NaBi3V2O10: A New Oxide Ion Conductor. J. Mater. Chem. 1998, 8, 281−282. (48) Wang, Q.; Liu, S.; Wang, X.; Fu, H.; Xu, J.; Lu, F.; Véron, E.; Allix, M.; Porcher, F.; Kuang, X. Aliovalent-Substitution Defect Chemistry, Crystalline-Glassy Phase Separation and Ionic Conductivity in Fresnoite Ba2TiSi2O8-Based Materials. Solid State Ionics 2015, 278, 157−165. (49) Islam, M. S.; Davies, R. A. Atomistic Study of Dopant SiteSelectivity and Defect Association in the Lanthanum Gallate Perovskite. J. Mater. Chem. 2004, 14, 86−93. (50) Kilner, J. A. Fast Oxygen Transport in Acceptor Doped Oxides. Solid State Ionics 2000, 129, 13−23. (51) Ruiz-Trejo, E.; Islam, M. S.; Kilner, J. A. Atomistic Simulation of Defects and Ion Migration in LaYO3. Solid State Ionics 1999, 123, 121−129. (52) Kagomiya, I.; Jimbo, K.; Kakimoto, K.-i.; Nakayama, M.; Masson, O. Oxygen Vacancy Formation and the Ion Migration Mechanism in Layered Perovskite (Sr,La)3Fe2O7‑δ. Phys. Chem. Chem. Phys. 2014, 16, 10875−10882. (53) Tomkiewicz, A. C.; Tamimi, M.; Huq, A.; Mcintosh, S. Oxygen Transport Pathways in Ruddlesden-Popper Structured Oxides Revealed via In-Situ Neutron Diffraction. J. Mater. Chem. A 2015, 3, 21864−21874.

(12) Ruddlesden, S. N.; Popper, P. New Compounds of the K2NiF4 Type. Acta Crystallogr. 1957, 10, 538−539. (13) Tealdi, C.; Ferrara, C.; Mustarelli, P.; Islam, M. S. Vacancy and Interstitial Oxide Ion Migration in Heavily Doped La2‑xSrxCoO4±δ. J. Mater. Chem. 2012, 22, 8969−8975. (14) Kuang, X.; Green, M. A.; Niu, H.; Zajdel, P.; Dickinson, C.; Claridge, J. B.; Jantsky, L.; Rosseinsky, M. J. Interstitial Oxide Ion Conductivity in the Layered Tetrahedral Network Melilite Structure. Nat. Mater. 2008, 7, 498−504. (15) Kendrick, E.; Kendrick, J.; Knight, K. S.; Islam, M. S.; Slater, P. R. Cooperative Mechanisms of Fast-Ion Conduction in Gallium-Based Oxides with Tetrahedral Moieties. Nat. Mater. 2007, 6, 871−875. (16) Kendrick, E.; Islam, M. S.; Slater, P. R. Developing Apatites for Solid Oxide Fuel Cells: Insight into Structure, Transport and Doping Properties. J. Mater. Chem. 2007, 17, 3104−3111. (17) Lacorre, P.; Goutenoire, F.; Bohnke, O.; Retoux, R.; Laligant, Y. Designing Fast Oxide-Ion Conductors Based on La2Mo2O9. Nature 2000, 404, 856−858. (18) Li, M.; Pietrowski, M. J.; De Souza, R. A.; Zhang, H.; Reaney, I. M.; Cook, S. N.; Kilner, J. A.; Sinclair, D. C. A Family of Oxide Ion Conductors Based on the Ferroelectric Perovskite Na0.5Bi0.5TiO3. Nat. Mater. 2014, 13, 31−35. (19) Li, M.; Zhang, H.; Cook, S. N.; Li, L.; Kilner, J. A.; Reaney, I. M.; Sinclair, D. C. Dramatic Influence of A-Site Nonstoichiometry on the Electrical Conductivity and Conduction Mechanisms in the Perovskite Oxide Na0.5Bi0.5TiO3. Chem. Mater. 2015, 27, 629−634. (20) Fujii, K.; Esaki, Y.; Omoto, K.; Yashima, M.; Hoshikawa, A.; Ishigaki, T.; Hester, J. R. New Perovskite-Related Structure Family of Oxide-Ion Conducting Materials NdBaInO4. Chem. Mater. 2014, 26, 2488−2491. (21) Jacobson, A. J.; Johnson, J. W.; Lewandowski, J. T. Interlayer Chemistry between Thick Transition-Metal Oxide Layers: Synthesis and Intercalation Reactions of K[Ca2Nan‑3NbnO3n+1] (3 ≤ n ≤ 7). Inorg. Chem. 1985, 24, 3727−3729. (22) Dion, M.; Ganne, M.; Tournoux, M. Nouvelles Familles de Phases MIMII2Nb3O10 a Feuillets “Perovskites. Mater. Res. Bull. 1981, 16, 1429−1435. (23) Schaak, R. E.; Mallouk, T. E. Perovskites by Design: A Toolbox of Solid-State Reactions. Chem. Mater. 2002, 14, 1455−1471. (24) Ishizawa, N.; Marumo, F.; Iwai, S.; Kimura, M.; Kawamura, T. Compounds with Perovskite-Type Slabs. V. A High-Temperature Modification of La2Ti2O7. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1982, 38, 368−372. (25) Ishizawa, N.; Marumo, F.; Kawamura, T.; Kimura, M. The Crystal Structure of Sr2Nb2O7, A Compound with Perovskite-Type Slabs. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1975, 31, 1912−1915. (26) Fujii, K.; Shiraiwa, M.; Esaki, Y.; Yashima, M.; Kim, S. J.; Lee, S. Improved Oxide-Ion Conductivity of NdBaInO4 by Sr Doping. J. Mater. Chem. A 2015, 3, 11985−11990. (27) Cherry, M.; Islam, M. S.; Catlow, C. Oxygen Ion Migration in Perovskite-Type Oxides. J. Solid State Chem. 1995, 118, 125−132. (28) Islam, M. S.; Cherry, M.; Winch, L. J. Defect Chemistry of LaBO3(B = Al, Mn or Co) Perovskite-Type Oxides. Relevance to Catalytic and Transport Behaviour. J. Chem. Soc., Faraday Trans. 1996, 92, 479−482. (29) Fisher, C.; Islam, M.; Brook, R. A Computer Simulation Investigation of Brownmillerite-Structured Ba2In2O5. J. Solid State Chem. 1997, 128, 137−141. (30) Khan, M. S.; Islam, M. S.; Bates, D. R. Dopant Substitution and Ion Migration in the LaGaO3-Based Oxygen Ion Conductor. J. Phys. Chem. B 1998, 102, 3099−3104. (31) Saiful Islam, M. Ionic Transport in ABO3 Perovskite Oxides: A Computer Modelling Tour. J. Mater. Chem. 2000, 10, 1027−1038. (32) Tealdi, C.; Mustarelli, P.; Saiful Islam, M. Layered LaSrGa3O7Based Oxide-Ion Conductors: Cooperative Transport Mechanisms and Flexible Structures. Adv. Funct. Mater. 2011, 21, 210−210. (33) Rietveld, H. M. A Profile Refinement Method for Nuclear and Magnetic Structures. J. Appl. Crystallogr. 1969, 2, 65−71. K


Acceptor Doping and Oxygen Vacancy Migration in ... - ACS Publications

Recommend Documents