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C: Energy Conversion and Storage; Energy and Charge Transport

Insights Into the Polymorphism of Lithium-Manganese Oxide, Li Mn O: A Comprehensive Survey of the High Pressure Properties 0.95

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Jolanta Darul, Catalin Popescu, Francois Fauth, and Pawel Piszora J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.9b03576 • Publication Date (Web): 19 Jul 2019 Downloaded from pubs.acs.org on July 30, 2019

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The Journal of Physical Chemistry

Insights Into the Polymorphism of LithiumManganese Oxide, Li0.95Mn2.05O4: A Comprehensive Survey of the High Pressure Properties Jolanta Darul1*, Catalin Popescu2, Francois Fauth2 and Paweł Piszora1 1Department

of Materials Chemistry, Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61-614 Poznań, Poland

2CELLS-ALBA

Synchrotron Light Facility, 08290 Cerdanyola, Barcelona, Spain

ABSTRACT Understanding the structural behavior of lithium manganese oxide (LMO) under high pressure, especially under non-hydrostatic pressure conditions, could provide more insights into control the mechanochemical processes occurring during battery operation and allow predicting new applications for this type of oxides. Here, we report pressure-induced structural changes in Li0.95Mn2.05O4 at two temperatures, 300 K and 380 K, investigated in situ through synchrotron X-ray powder diffraction up to 13 GPa in a diamond anvil cell. Compressioninduced strain triggers a cascade of local structure deformations which finally result in the

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structural phase transition to the high-pressure tetragonal phase. Comparison of bulk moduli at two temperatures reveal that, due to the differences in the response of the structure to the strain, Li0.95Mn2.05O4 exhibits the rare property of “warm hardening”. Additionally, a direct correlation between hydrostaticity of the pressure-transmitting medium and structural transformations was found. Our findings demonstrate that high pressure can be a robust tool to tune the structural properties and provide insights into the relationship between the strain and the structure of lithium manganese oxides under extreme conditions.

INTRODUCTION Spinels form a very large family, and they can comprise from only one cation e.g. in Mn3O4 up to five or more metal elements in oxides with interesting novel and unexpected properties e.g. (Co,Cr,Fe,Mn,Ni)3O4

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which belongs to a new family of high entropy oxides, promising in

reversible electrochemical energy storage.2 Lithium-ion batteries with spinels as the electrode materials are intensely pursued as energy storage devices because they provide high energy and power. Lithium-manganese spinel, LiMn2O4, has been proposed also as a matrix for the isotopic separation of 6Li, and different scale-up possibilities have been numerically simulated for this material.3,4 Operating in the spinel structure with chemical composition, temperature and pressure opens up the possibility of obtaining novel materials showing useable properties. Stoichiometric lithium-manganese spinel LiMn2O4 crystallizes in a cubic close-packing of oxygen atoms (Fdm space group) with Li+ ions in ¼ of tetrahedral sites and 1:1 ratio mixture of Mn3+ and Mn4+ ions distributed over ½ of the octahedral sites. Previous studies on LiMn2O4 have established that it undergo high pressure high temperature (HPHT) phase transition to an orthorhombic postspinel structure.5 The non-stoichiometric counterpart, Li0.95Mn2.05O4, has the


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ability to switch between three types of crystal structure depending on a manifested cooperative Jahn-Teller effect.6

Jahn–Teller Effect Mn3+-based lithium-manganese spinel with unusual structural properties is of particular interest. In octahedral environment, where the eg orbitals point directly at oxygen ligands, the Jahn–Teller distortion results in a large energetic stabilization of Mn3+ (Figure 1). Similarly strong Jahn–Teller effect in octahedral spinel sites occurs for Cr2+ and Cu2+ ions. In tetrahedral site an energetic stabilization, and strong Jahn–Teller effect, occurs because of unevenly occupied t2 orbitals. Such a strong deformation in tetrahedral sites can be observed also for such ions as Mn4+, Cr3+, Cr2+, V2+, Ni2+, Cu2+.7.8 In practice, however, many of these ions do not occupy spinel tetrahedral sites because of lower preference for these positions. For example, Mn4+ ion has such a large stabilizing energy in the octahedral crystalline field that it would never occupy a tetrahedral position. In multisublattice oxide compounds of spinel structure distortion in one sublattice causes strain and acts as a nucleation center for inducing the cooperative Jahn–Teller effect in all Jahn–Teller active sublattices. Jahn–Teller effects produce local site distortions which is able to switch among different axes. The vast majority of manganese(III) compounds are known to occur in a high-spin state with the Mn3+ ion at the center of elongated octahedron, which is related to the fact that the elongated Mn(III) octahedra show favorable magnetic anisotropy. Compounds with the compressed Mn(III) octahedra are very rare and scientifically interesting.9 Even less frequent than the compound with the compressed Mn(III) octahedra is the oxide system in which two


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types of distorted octahedrons are present side by side in the same structure – elongated and shortened. So far, Mn5VO8 is the only known oxide showing this property.10

Figure 1. Splitting of d energy levels for Mn3+ ion and involved tetragonal distortions in tetrahedral and octahedral coordinations. Strain in Spinels For a series of manganese(III) complexes it has been found that the strain resulting from angular distortion of the ligands is the factor that controls the type of Jahn–Teller distortion. In the complexes in which the angular distortion of the first coordination sphere imposed by a polydentate ligand is great, the compressed octahedra are observed. Axially elongated octahedra in manganese(III) complexes are commonly attributed to the additional stabilization of the 3dz2 orbital via the interaction with the 4s orbital and anharmonic contributions to the vibrational


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potential, however just a small swing of the strain vector is needed for the compression of Mn(III) octahedron to be competitive.11 Correlations between the subtle fluctuations in chemical composition and the resulting from them structural changes bring modifications of mechanical properties. Increase in the oxidation state of manganese in the spinel structure, e.g. on Ni/Fe doping of LiMn2O4, reduces the lattice parameter and finally changes the mechanical properties of lithium-manganese spinel.12 The structural and electrochemical properties of LiMn2O4 appear to be sensitive to the thermal treatment. The post-annealing process leads to a better crystallinity and suitable strain in the lithium manganese oxide, enhancing the electrochemical properties.13 Either too high or too low strain can cause instabilities of the structure. The source of such strain may be, e.g. the Jahn– Teller effect. Mechanical response of the lithium-manganese oxide as an electrode is highly coupled to the electrochemical performance of a lithium ion battery. It has been observed that LiMn2O4 with nanorods morphology can accommodate more stress compared to their bulk counterparts.14 Understanding of these complex relationships is essential for proper design of lithium-ion batteries. The strong coupling between chemical composition and mechanical properties has been reported also for Li-Ni-Mn spinels, where a substantial difference in bulk modulus between oxides with different Ni content was found.15 Thus a combination of the macroscopic stress fields with chemical interactions on the atomic scale has significant technological and economic potential. The unique properties of the material studied in this work stem from the relatively rare distribution of ions at two crystallographic positions. At the octahedral position the crystal field splits the fivefold d levels of the cation into higher twofold eg levels and lower threefold t2g levels (left two columns in Fig. 1). Further energy gain occurs through the subsequent break in


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the degeneracy of eg and t2g levels and Jahn–Teller distortion of Mn3+O6 octahedron. In lithiummanganese spinel LiMn2O4, monovalent Li+ cation occupies the tetrahedral A sites and octahedral B sites are occupied by half to half mixture of Mn4+ and Jahn–Teller active Mn3+ ions. The reduction of the number of lithium atoms at tetrahedral sites, as in Li0.95Mn2.05O4, allows the supplementation of tetrahedral sites with Mn3+ ions. The correlation between the positions and the strain introduced by such a small number of Mn3+ ions at the tetrahedral sites results in the Jahn–Teller's distortion of tetragonal symmetry and c/a’ < 1. The two types of tetragonal deformation, characterized with c/a’ < 1 and c/a’ > 1, are known in the Fe1-xMnxCr2O4 system, where a Jahn–Teller active ion is Fe2+ and Mn2+ dilute it at tetrahedral sites.16 The complex phase diagram of Fe1-xMnxCr2O4 has been explained by the competition between the compression of FeO4 tetrahedra, caused by the lattice anharmonicity, and its elongation induced by spin-orbit coupling of the Fe2+ ions. The unquestionable and well-established position of lithium-ion batteries in energy storage technologies requires continuous optimization of their positive electrodes. Lithium manganese oxides are key materials for the construction of batteries with high energy, high power, and long cycle life. Lithium-manganese oxide with a tetragonal structure plays an important role in optimizing alsolid-state batteries performance. Lattice strain at the heterointerface induce tetragonal symmetry of lithium-manganese oxide what reduce the lattice misfit parameter and improve electrochemical performance of such batteries.17 Tetragonal LMO is a key material in the new concept for the design of charge electrode materials. The unique tetragonal spinel phase combines the behavior of a pseudocapacitor and a battery, which results in slowing down the self-discharge process and enhance both the cycle stability and the capacity.18


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Testing the behavior of the lithium manganese oxide under high pressure, especially under non-hydrostatic pressure conditions, helps understand the relation between the material compression and Jahn–Teller deformation, control the elastic strain induced by lattice mismatch at the thin-film interface and tune mechanochemical processes.19 Hereafter we demonstrate the complicated pressure-induced structural changes in Li0.95Mn2.05O4, taking also into account the influence of both pressure and temperature. EXPERIMENTAL SECTION The Li0.95Mn2.05O4 spinel sample was obtained from the appropriate amounts of thoroughly mixed powders of α-Mn2O3 and Li2CO3 (99.0% Merck) by thermal treatment in air at 1048 K. After heating, the specimen was quenched rapidly in solid CO2. Structural analyses showed the expected stoichiometry of the obtained powder and confirmed that no spurious phases were present. Transmission electron microscope (TEM) images were recorded on a Hitachi HT7700 microscope, operating at accelerating voltage of 100 kV. They were used to monitor the morphology and structural properties of the sample, as well as for elemental analysis with the help of energy dispersive X-ray spectroscopy EDS/TEM. To prepare the TEM sample, the material was deposited on copper grids coated with a carbon film. The chemical composition of the spinel sample was analyzed by inductively coupled plasma optical emission spectroscopy (Varian ICP-OES VISTA-MPX). ICP-OES analysis confirmed the nominal cation ratio in the prepared lithium–manganese oxide. More details on the preparation of the sample and on the determination of the Li/Mn ratio is reported elsewhere.6 TG measurements were run by means of a Setsys 1200 (Setaram) system with a heating rate of 10K min−1 in air. Thermogravimetric analysis (see Figure S3, Supporting Information) indicated that the evident


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mass loss upon heating occurs only if the temperature exceeds 1170 K, therefore, at the synthesis temperature of 1048K, thermal dissociation and formation of anionic vacancies is ruled out. The structural properties of Li0.95Mn2.05O4 at high pressure and at two temperatures, 300 K and 380 K, were studied in situ up to 13 GPa by means of powder angle-dispersive X-ray diffraction. The measurements were conducted at the MSPD-BL04 beamline20 of the ALBA Synchrotron Light Source using monochromatic radiation, at a wavelength  = 0.4246 Å, and a beam size of 20 µm x 20 µm (FWHM). High pressure (HP) and high pressure high temperature (HP/HT) experiments were carried out by using a membrane-type diamond anvil cell (DAC). A pair of 300 µm culet-size diamond anvils was used. Gaskets made from rhenium, pre-indented to a thickness of ~60 µm and then drilled to a diameter of ~140 µm, served as the sample chamber. The powder sample was placed between two diamonds. A piece of gold with a purity of 999.9 and of about 30 µm in diameter was loaded into the sample chamber as a pressure marker. The cell pressure was determined using the equation of state for gold.21 Gold has been chosen as a pressure standard because of its moderate compressibility, chemical inertness, and large X-ray scattering power. The pressure transmitting medium was a polydimethyl-siloxane oil of the type ‘Rhodorsil 47V1000’ (VCR) which behaves hydrostatically at room temperature up to 2.5 GPa and quasi-hydrostatically up to 10 GPa with a pressure gradient of 0.4 GPa.22 As a general rule, the hydrostatic pressure range can be easily increased by heating but there is no reported study this type of silicone oil to support this information. The DACs were heated using a resistiveheating system commercially available from Betsa-France. The temperature was measured using a K-type thermocouple attached to one of the diamond anvils. The system was allowed to equilibrate for ~600 s at each pressure point. Diffraction images were taken using a Rayonix CCD detector with 165mm diameter sensitive surface then the diffraction patterns were


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integrated to generate the conventional one-dimensional profiles using the Fit2D program.23 Analyses of all the patterns were carried out by means of the Rietveld refinement procedure implemented in the EXPGUI/GSAS software package.24,25 For all patterns, the diffraction peak profile was fitted with pseudo-Voigt functions. The background was fitted with a four-term Chebyshev polynomial of the first kind, based on the manually defined background points. Prior to refinement, at each pressure, profile parameters were fitted and fixed during the final refinement. The refined parameters (maximum 11 parameters) were: zero shift, lattice parameters, oxygen coordinates in spinel phases and lattice parameters in Re (gasket). Anisotropic peak broadening mainly caused by lattice strain was observed with broadening of the diffraction peaks. The phenomenological microstrain model of Stephens with 4 and 2 refinable parameters for tetragonal and cubic symmetry respectively was used to model the anisotropy in FWHM of the individual peak profiles. This microscopic image was completed by analyzing the isosurface of the anisotropic microstrains which reflects the strong shear strain of neighboring coordination polyhedrons in the lithium manganese structure. For volume changes as a function of pressure, the data were fit to the isothermal Birch– Murnaghan equation of state using EosFit7-GUI26,27 to detfermine the bulk modulus (K0) of each sample. The order of the Birch–Murnaghan equation was chosen on the basis of the slope of normalized pressure versus strain, taking into consideration the error bars. Because there was almost no change in the normalized pressure as a function of strain (K0′ = 4), the second-order Birch–Murnaghan equation was used. RESULTS To study a microstructure of the prepared Li0.95Mn1.95O4 material, TEM studies have been conducted along with EDS mapping. The representative bright field image, TEM and elemental


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mappings are shown in Fig. S2 (Supporting Information). The reflections corresponding to the constituent elements (Figure S2 d) confirmed that the synthesized sample was pure and composed of only Mn and O (the Cu signal is originated from the copper grid support for EDS analysis). However, it is important to note that the Li peak is not present for the sample due to the fact that EDS is incapable of detecting the elements such as hydrogen, helium and lithium, since at least two electrons are needed for the process to occur. The EDS elemental maps in Figures S2 b and c confirm that the Mn and O were homogenously distributed on the surface and there is no significant agglomeration of Mn or composition separation. X-ray diffraction patterns for the sample Li0.95Mn2.05O4 collected at pressure and temperature conditions of the present experiment showed that phase transitions were observed with increasing pressure both at 300K and at 380K. Figure 2 shows representative synchrotron powder X-ray diffraction patterns at various pressures collected upon two isothermal compression cycles at 300K and 380K. It was difficult to fully separate the reflections belonging to each phase and quantitatively determine their relative abundance, especially the strong overlap of 211 and 103 reflections coming from both tetragonal phases is particularly noticeable. However, both qualitative and quantitative analysis could be carried out successfully applying the Rietveld refinement because with this method complex and seriously overlapping patterns can be analyzed.


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Figure 2. Representative synchrotron XRD patterns of Li0.95Mn2.05O4 collected at selected pressures (a) at 300 K, (b) at 380 K. Stars indicate the positions of the peaks for rhenium (gasket). The hkl indices are indicated for the most representative diffraction peaks of: (a) bottom – the ambient pressure tetragonal phase (space group I41amd; c/a’ < 1); (b) bottom – ambient pressure cubic phase (space group Fdm); (a) and (b) top – the high pressure tetragonal phase (space group I41amd; c/a’ > 1). The background was subtracted in all spectra. The overall diffraction features of LMO material appear to remain relatively unchanged until 0.40 GPa and 0.73 GPa at 300 K and 380 K respectively. Most elements of the starting XRD pattern clearly visible in the region 9° – 11° 2θ (see Figures S1 and S5) can still be discerned in


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the data obtained at 4.93 GPa and 5.75 GPa at temperature of 300 K and 380 K, respectively. However, in this diffraction region you can see the appearance and continuous increase in the intensity of reflections from the high-pressure phase. Further analysis by examining the V(P) relations was carried out using Rietveld refinement method. Assuming the initial tetragonal phase, Tf (c/a’ < 1), when fitting the diffractograms recorded at higher pressures resulted in the best match of the profile and in significantly smaller values of the error indices, therefore this phase was considered for all pressures.

Figure 3. Final observed and calculated synchrotron X-ray ( = 0.4246 Å) powder-diffraction profiles for the Li0.95Mn2.05O4 sample at 300 K and at (a) 5.75 GPa, (b) 0.0001 GPa, at 380 K and (c) 5.31 GPa, (d) 0.0001 GPa. Agreement indices – (a): χ2 = 0.57, Rwp = 1.02, R(F2) = 6.43; (b): χ2 = 0.62, Rwp = 1.52, R(F2) = 5.36; (c): χ2 = 0.8, Rwp = 0.06, R(F2) = 8.06; (d) χ2 = 0.6,


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Rwp = 0.72, R(F2) = 4.62. The lower solid lines show the difference profiles. The insets show enlarged areas of the diffraction patterns in the region of the 311 cubic spinel line. Figure 3 shows the Rietveld refinement to the XRD data recorded for Li0.95Mn2.05O4 sample at ambient pressure both at 300 K and 380 K. Moreover, the refinements of two example patterns collected at high pressure are also presented. In the pattern collected at ambient pressure and at 300 K (Figure 3b), all the observed diffraction peaks were indexed to a tetragonally distorted spinel structure with the I41/amd space group and c/a’ < 1, for simplicity hereinafter referred to as Tf. This unique type of distortion results from a superimposition of two Jahn–Teller local deformations – elongation of more than half of octahedrons occupied by Mn3+ ions and flattening of barely 5% of tetrahedrons due to presence of Mn3+ ions which in the tetrahedral environment generate flattened deformation. These two opposing deformations do not counteract each other, as in Ni1−xCuxCr2O4,28 but a small number of Mn3+ at tetrahedral positions control the manganese ions at octahedral sites, switching their deformation from stretched to flattened. This type of unit cell flattening (c/a’ < 1) has been observed in the high-pressure structure of Mn3+[Ni2+Mn3+]O4, in which the tetrahedrally coordinated Mn3+ cations imposed deformation on the crystal structure, despite the presence of Mn3+ cations at the octahedral positions, which alone act in the opposite direction.29 It can be easily seen that heating the sample by only 80 K, to 380 K, caused elimination of the tetragonal distortion. In the pattern collected at ambient pressure and at 380 K (Figure 3d), all the observed diffraction peaks have been indexed to a cubic spinel structure with the Fdm space group, hereinafter referred to as C. Moreover, Rietveld analysis showed that both at 300 K and 380 K, an increase in pressure triggers a phase transformation into the tetragonal phase with the I41/amd space group and c/a’ > 1 (Figures 3a and b), for simplicity


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hereinafter referred to as T. Peaks assigned to rhenium (gasket) were also considered in the refinement.

Figure 4. Fraction of the high-pressure tetragonal phase, T, at 300 K (circle) and at 380 K (diamond). Error bars are comparable to symbol sizes. Figure 4 presents the changes in the content of the tetragonal high-pressure phase (c/a’ > 1) with increasing pressure. The increase in temperature only slightly shifts the pressure limit at which the new phase appears. However, a significant difference is noticeable if you look at the maximum contribution of this phase. With increasing temperature the formation of the highpressure phase is preferred. It should be noticed that at 300 K and 380 K there are two different initial crystalline phases the tetragonal one with c/a’ < 1 and the cubic one, respectively. Preheating of the tetragonal phase with c/a’ < 1 to 380 K removes the tetragonal deformation, and thus also removes the cooperative Jahn–Teller effect. Such a structure, without ordering of the 3dx2-y2 and 3dz2 orbitals, as in the tetragonal phase with c/a’ < 1 (Tf), is much susceptible to reordering of the orbitals, in this case due to high pressure.


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Figure 5. (a–b) Pressure dependences of the lattice parameters a, and c of LMO. (c–d) Lattice volume as a function of pressure for LMO. For the cubic phase we plotted a/√2 instead of a and V/2 instead of V for the sake of comparison. Error bars are comparable to symbol sizes.


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Figure 6. Variation of the distortion parameter c/a’ (a’ = √2a) in LMO with pressure (solid circles) and pressure dependence of the standard deviation σ in silicone oil ‘Rhodorsil 47V1000’ as PTM based on the literature data22 (open circles). On the basis of the results obtained from the Rietveld refinement, we plotted a(P), c(P) and V(P) relations for both phases at each temperature (Figure 5). These plots revealed a relatively complex compressibilities in the tested pressure range. In order to unravel these complicated relationships, we compiled in Figure 6 the pressure dependencies of changes in the c/a’ distortion parameter and σ parameters. The standard deviation, σ, of pressure has been considered to be an extremely sensitive criterion for solidification of PTM and an indicator of the hydrostaticity of the pressure transmitting medium.22 Overlapping of diffraction peaks in conditions in which two phases are observed significantly hinders separation of crystalline size and strain effect. However, analysis of non-splitted spinel 111 peak (see Figure S4) supports our observations of lattice volume changes as a function of pressure (Figure 5c and d). In the phase transformation region of pressure at 300 K one can notice the widening of the peak due to the difference in the volume of the low and high pressure


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phases. At 380 K, this effect is not observed, which corresponds well to almost identical volumes of both phases observed in Figure 5d. A strong dependence of the degree of tetragonal deformation of the spinel structure on nonhydrostatic pressure components can be observed. These sensitivity to hydrostaticity of the pressure transmitting medium provided the evidence that the pressure-induced transformations are actually the strain induced ones, and could help to explain the apparently unnatural physical deflection in linear and volumetric compressibilities. Decrease in the c/a’ distortion parameter (Figure 6) and the unit cell volume (Figure 5c) in the pressure range up to about 2.5 GPa is in good agreement with literature22, assuming that this pressure is the hydrostaticity limit in the applied PTM. It has been found that LiMn2O4 is extremely sensitive to the nonhydrostatic conditions. The pressure-induced phase transitions in this material were observed at about 11 GPa, i.e. about the hydrostaticity limit of the applied in those experiment methanol–ethanol mixture.14 Above 2.5 GPa we observed a complex pressure dependence of the c/a’ distortion parameter and slower decrease in volume, characteristic of the nonhydrostatic condition. Beyond this point, the pressure across the experimental volume is generally inhomogeneous and differential (mostly uniaxial) stress and shear stresses appear22. Under non-hydrostatic conditions there is a non-negligible deviatoric stresses which can reduce the compressibility of oxides and increase the bulk modulus.30 Such behavior was reported in boron suboxide for which the bulk modulus is ranging from 124 to 363 GPa depending on the experimental conditions.31 Increase in temperature to 380 K moves this point of sharp volumetric change to about 5 GPa (Figure 5d). This behavior matches well with the increase of hydrostatic limit by heating as commented earlier.


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Regardless of the measurement temperature (300 or 380K), the appearance of anomalies in linear and volumetric compressibility are in coincidence with the almost total presence of highpressure tetragonal phase (Figures 4 and 5). With such a large impact of changes in the hydrostaticity of the pressure medium on elastic and structural parameters, it is not possible to determine one value of the bulk modulus for the entire tested pressure range. As the saying “you can't have your cake and eat it” goes, a breakneck challenge is the determination of the bulk modulus (defined in hydrostatic conditions), and simultaneous observation of phase transformations caused by non-hydrostatic pressure. The complex dependences of the lattice parameters and the lattice volume on pressure (see Fig. 5) forced us to resign from determining the bulk modulus in the full range of pressure and to calculate K0 in limited regions only. The V(P) curve was analyzed using least squares methods to estimate K0. High pressure V(P) data for lithium manganese oxide was fitted using a Birch– Murnaghan (BM) equation of state. A linear fit in the lowest pressure range, below 1 GPa, yields bulk modulus of K0 = 108 ± 9 GPa and K0 = 103 ± 11 GPa for 300 K and 380 K, respectively. The first pressure derivative of the bulk modulus was fixed to 4. At both temperatures, values of the bulk modulus are identical, within the measurement uncertainty, and they are comparable with the literature data for LiMn2O4 (K0 = 119 ± 4 GPa,14 K0 = 111 ± 2 GPa32) and Li4Mn5O8 (K0 = 118 ± 1 GPa33). However, in the wider pressure range the pressure-induced change in the unit cell volume is not in compliance with those observed for spinels with higher lithium content. Above 1 GPa the slope of volumetric changes tend to be lower and calculated bulk moduli are K0 = 129 ± 8 GPa and K0 = 224 ± 5 GPa for 300 K and 380 K, respectively (Fig. 7a). Increase in the bulk modulus value is a consequence of lattice strain generated in the pressure region where the phase transition to the high-pressure tetragonal phase (T) occurs. Strange as it may seem, the


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bulk modulus at 380 K has a value higher than at 300 K. Usually heating release strain and it should results in protection against the increase of the bulk modulus. However, in Li0.95Mn2.05O4 at 300 K the phase transition to the tetragonal phase with c/a’ > 1 precedes the increase in tetragonal distortion of the initial tetragonal phase with c/a’ < 1. Such a compensation of the lattice strain leads to coexistence of two tetragonal phases in a wide pressure range (Fig. 4). At 380 K, the elevated temperature led to the fading of the cooperative Jahn–Teller effect and the initial lattice strain was accumulated in the cubic structure, leading to an increase in its bulk modulus. Therefore, Li0.95Mn2.05O4 exhibits the very rare property of “warm hardening” whereby its bulk modulus or stiffness increases with temperature.34 The different mechanism of the phase transition lead to almost complete transformation of the cubic phase to the tetragonal phase with c/a’ > 1. The temperature of 380 K caused the shift of the end of the phase transition up to about 5 GPa. To focus further on this observation we transformed the data into a normalized pressure vs. Eulerian strain (F–f) diagram (Figs. 7b,c). with the Eulerian strain parameter f given by fE = ½[(V0/V)2/3 − 1]. Normalization of the pressure to a variable F = P/[3fE (1 + 2fE)5/2] and plotting the graph F vs. f confirms the choice of the 2-order BM EOS in the two pressure regions 1 – 2.5 GPa and 1 – 5 GPa for data collected at 300 K and 380 K, respectively. No straight line slope means that K0’ can be fixed at 4 and intercept of linear function as f → 0 confirms the calculated values of K0.


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Figure 7. Volume compression of Li0.95Mn2.05O4 at high pressure both at 300 K and at 380 K (a). The solid and the dashed lines represent the fit of the second-order Birch–Murnaghan equation of state in two regions of pressure. Normalized pressure as a function of Eulerian strain at 300 K (b) and at 380 K (c). Going beyond the pressure range discussed above, the coexistence of two crystalline phases and variation of hydrostaticity result in some unexpected changes in the slope of the F(f) plot, which implied an extremely high and nonphysical value of the calculated bulk modulus. Such an anomalous elastic behavior has been observed in many materials and it has been widely explained by hardening of the pressure transmitting medium after solidification and high shear


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stress.35 Moreover, in silicone oil (PTM), interactions between the long-chain molecules introduce the nontrivial elastic properties and fluctuations in the pressure transmittance.36 The elastic behavior and the structural evolution of lithium-manganese oxide compressed in the pressure-transmitting fluid is drastically affected by the potential crystal–fluid interaction in response to the applied pressure.

Figure 8. Relative lengths of the crystallographic axes in the tetragonal phase with c/a’ < 1 (Tf) at pressures up to 3 GPa. Dashed lines are the guide for the eye. An interesting trend is observed for the pressure dependencies of the relative lattice parameters, a/a0 and c/c0, (Figure 8). Isotropic compression of the unit cell in Tf phase is observed up to ~1.5 GPa, whereas above this pressure, the pressure-induced change in a and c parameters reveal anisotropy of the unit cell compression, even in the pressure range for which PTM has provided hydrostatic conditions. There is a significant difference between the contraction rates of the intraplanar periodicity a and the interplanar periodicity c, the latter is reduced by about 1.4 times faster than the former, which means that the structure is more compressible in the c direction than in the a/b direction. Linear compressibilities in the region


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1.5 – 2.5 GPa are: M0(c) = 193(16) (W-χ2 = 1.74) and M0(a) = 720(143) (W-χ2 = 6.34). This is consistent with the arrangement of the (Li,Mn)O4 tetrahedra and MnO6 octahedra in the unit cell. The anisotropic compression is related with the fact there are not (Li,Mn)O4 tetrahedra in between the MnO6 octahedra along the c-axis direction. Lithium manganese oxide, LiMn2O4, is considered to be extremely sensitive to deviatoric stress induced by external applied pressure. However, the presence of multiple phases including the tetragonal c/a’ > 1, tetragonal c/a’ < 1, and the cubic structure in nonhydrostatic conditions excluded obtaining detailed structural data for LiMn2O4.14 Li0.95Mn2.05O4, unlike stoichiometric lithium-manganese oxide, undergoes in nonhydrostatic conditions the well-defined phase transition and quantitative determination of the relative contribution of the high-pressure phase was not complicated.


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Figure 9. Changes in the (Li,Mn)O4 and MnO6 polyhedra as a function of pressure: tetrahedral angle (a, b, c), polyhedral interatomic distances (d, e, f) and polyhedral angle variance (g, h, i) vs pressure. Circles and diamonds refer to Tf and T phase, respectively. The lines are guide for the eye. Let's focus our attention on the local deformation of polyhedrons. The angle variance (σ2) of the polyhedron is a measure of the distortion of the bond angles from their ideal value of 109.47° and 90° in tetrahedron and octahedron, respectively.37 The angle variance for a regular octahedron would be zero. Pressure does not change the deformation of octahedra up to ~9 GPa both in Tf and T phases at 300 K, as evidenced by the plot of the angle variance parameter (Fig.


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9h). However, significant changes in deformation of tetrahedra are observed in both Tf and T phases (Figs. 9a and b). Monotonic convergence of tetrahedral angles to the ideal value of 109.47° reveals that with increasing pressure the tetrahedron in the T phase becomes more regular, eventually it becomes regular at 12.15 GPa. This simple dependence of the tetrahedral angle on pressure indicates that there is no relationship between the deformation of the tetrahedron and the hydrostaticity of PTM. The tetrahedral angle in phase Tf behaves in a completely different way, it remains almost unchanged until the nonhydrostatic component of pressure begins to rise (at about 2 GPa), then there is a sudden elongation of tetrahedron. The gradual increase in deformation of tetrahedron ceases and the phase transition to the highpressure T phase ends. In the region of the highest pressures the measurement uncertainties increase, which does not allow interpretation of relatively small changes in the tetragonal angle. The changes in the tetrahedron deformation, represented by the changes in the tetrahedral angle and shown in Figure 9a, clearly indicate that the cause of structural changes in the Tf phase is the non-hydrostatic pressure component. Furthermore, these structural changes precede the phase transition to the high-pressure T phase. The octahedra in the Tf phase undergo flattening with increasing pressure up to about 5 GPa, whereas for higher pressures this local deformation remains unchanged in the sigma limit (Fig. 9d). What is characteristic of this deformation, a significant axial shortening of the two Mn-O bonds coincides with a slight extension of the four equatorial bonds. Pressure promotes the Jahn– Teller flattening of the octahedra leading to their slightly negative linear compressibility in the z direction. The region of changes in the local octahedron deformation coincides with the pressure range in which the pressure-induced phase transition takes place most intensively (Fig. 4). In the T phase at pressures between 2 and 9 GPa, the only noticeable change in the interatomic


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distances is the shortening of the four equatorial Mn-O distances, which results in an increase in the octahedral Jahn–Teller deformation (Fig. 9e). In contrast, the tetrahedral bond distances do not change significantly with pressure in the range between 2 and 9 GPa, i.e. the only way the tetrahedra are distorted is the change in the angles between the bonds. Heating the sample to 380 K causes substantial changes in local distortions. Changes in the tetrahedral angles imply that in the T phase at 380 K, increasing pressure forces the tetrahedron to be more regular up to the pressure of ~5 GPa (Fig. 9c). This pressure dependence of the tetrahedral angle is more significant than at 300 K, however at ~5 GPa it stops at the angle values of about 106° and 111° and does not converge to 109.47° with further compression. Also, important changes are observed in interatomic distances up to 5 GPa. The four octahedral equatorial distances are shortened, but specifically, in contrast to 300 K also the tetrahedral (Li,Mn)-O bond length increases in this pressure region (Fig. 9f). Unlike at 300 K, an increase in the octahedral angle variance can be observed at 380 K (Fig. 9i), however, for pressures above 5 GPa, a plateau can be observed.

CONCLUSIONS To sum up, we have presented a new insight into the pressure (strain) induced structural transformations in LMO, observed at two temperatures for tetragonal (c/a’ < 1) and cubic spinel phase. At two temperatures, 300 K and 380 K, the influence of high pressure on LMO crystal structure was studied using synchrotron radiation and the diamond anvil cell. In the tetragonal form of the lithium-manganese oxide, Li0.95Mn2.05O4, at 300 K the flattened MnO6 octahedrons reveal a unique electron configuration, which is completely different from that in the regular phase, in which heating of the sample by only 80 K causes a removal of the


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tetragonal distortion. Nevertheless, both of these phases transform to the tetragonal phase with c/a’ > 1, under compression. A direct correlation between hydrostaticity of the pressure-transmitting medium and structural transformations was found. The non-hydrostatic pressure component induces in the structure a local deformation of coordination polyhedron, enhances the Jahn–Teller deformation and eventually causes a phase transition to the high-pressure tetragonal phase with c/a’ > 1. This tetragonal phase arises under pressure in the compounds in both the tetragonal phase with the distortion parameter c/a’ < 1 (at 300 K) and the cubic phase (at 380 K). The rate of structural conversion of the tetragonal phase with c/a’ < 1 is lower than of the cubic phase, which can be explained by more strain accumulation in the Jahn–Teller deformed Mn-containing polyhedrons. We found that Li0.95Mn2.05O4 exhibits the very rare property of “warm hardening”. We link the increase in the bulk modulus value vs. temperature with different models of compensation of the lattice strain in the tetragonal and in the cubic phase. We found that the pressure promotes the anisotropy change in the tetrahedral position of the low temperature phase, however in the high pressure tetragonal phase (Li,Mn)O4 tetrahedra become more regular. The relative lengths of the crystallographic axes reveal isotropic compression of the initial tetragonal phase with c/a’ < 1, Tf, up to about 2.5 GPa, thereafter the compression induces reduction of the tetragonal deformation of the spinel lattice. Considering the great potential of LMO materials related to the possibility of controlling the Jahn–Teller effect with the pressure (strain), they can be undoubtedly further optimized, and finding new applications for them is just a matter of time.


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ASSOCIATED CONTENT Supporting Information: XRD measurements, TEM images, EDS spectrum and elemental mapping, TG measurement, FWHM of the single peak in the cubic spinel 111 line region from the sample, pressure/temperature dependent results of Rietveld refinement. AUTHOR INFORMATION Corresponding Author [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS These experiments were performed at the MSPD-BL04 beamline at ALBA Synchrotron with the collaboration of ALBA staff. REFERENCES [1] Dąbrowa, J.; Stygar, M.; Mikuła, A.; Knapik, A.; Mroczka, K.; Tejchman, W.; Danielewski, M.; Martin, M. Synthesis and microstructure of the (Co, Cr, Fe, Mn, Ni)3O4 high entropy oxide characterized by spinel structure. Mater. Lett. 2018, 216, 32–36.


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[2] Sarkar, A.; Velasco, L.; Wang, D.; Wang, Q.; Talasila, G.; de Biasi, L.; Kübel, C.; Brezesinski, T.; Bhattacharya, S. S.; Hahn, H.; Breitung, B. High entropy oxides for reversible energy storage. Nat. Commun. 2018, 9, 3400. [3] Okano, K.; Takami, Y.; Yanase, S.; Oi, T. Lithium isotope effects upon electrochemical release from lithium manganese oxide. Energy Proced. 2015, 71, 140–148. [4] Acosta, L. N.; Flexer, V. A first assessment on the scale-up possibilities of different electrochemical techniques for lithium isotopic enrichment. Ind. Eng. Chem. Res. 2018, 57(33), 11399–11413. [5] Yamamura, K.; Huang, Q.; Zhang, L.; Takada, K.; Baba, Y.; Nagai, T.; Matsui, Y.; Kosuda, K.; Takayama-Muromachi, E. Spinel-to-CaFe2O4-type structural transformation in LiMn2O4 under high pressure, JACS 2006, 128, 9448–9456. [6] Darul, J.; Lathe, C.; Piszora, P. Hooked on switch: strain-managed cooperative Jahn–b n Teller effect in Li0.95Mn2.05O4 spinel. RSC Adv. 2014, 4(110), 65205-65212. [7] Tarantino, S. C.; Giannini, M.; Carpenter, M. A.; Zema, M. Cooperative Jahn–Teller effect and the role of strain in the tetragonal-to-cubic phase transition in MgxCu1−xCr2O4. IUCrJ 2016, 3(5), 354–366. [8] Efthimiopoulos, I.; Tsurkan, V.; Loidl, A.; Zhang, D.; Wang, Y. Comparing the pressureinduced structural behavior of CuCr2O4 and CuCr2Se4 spinels. J. Phys. Chem. C 2017, 121(30), 16513–16520.


28

Page 29 of 33 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


[9] Wang, S.; He, W.R.; Ferbinteanu, M.; Li, Y.H.; Huang, W. Tetragonally compressed highspin Mn (III) Schiff base complex: Synthesis, crystal structure, magnetic properties and theoretical calculations. Polyhedron 2013, 52, 1199–1205. [10] Clemens, O.; Haberkorn, R.; Kohlmann, H.; Springborg, M.; Beck, H. P. Synthesis and characterization of the new mixed valent compound Mn5VO8. Z. Anorg. Allg. Chem. 2012, 638(7‐8), 1134–1140. [11] Tregenna-Piggott, P. L. Origin of compressed Jahn−Teller octahedra in sterically strained manganese(III) complexes. Inorg. Chem. 2008, 47(2), 448–453. [12] McGrogan, F. P.; Chiang, Y.-M.; Van Vliet, K. J. Effect of transition metal substitution on elastoplastic properties of LiMn2O4 spinel. J. Electroceram. 2017, 38, 2-4, 215-221. [13] Yao, J.; Shen, C.; Zhang, P.; Gregory, D. H.; Wang, L. Enhanced cycle ability of spinel LiMn2O4 by controlling the phase purity and structural strain. J. Phys. Chem. Solids 2012, 73(11), 1390-1395. [14] Lin, Y.; Yang, Y.; Ma, H.; Cui, Y.; Mao, W. L. Compressional behavior of bulk and nanorod LiMn2O4 under nonhydrostatic stress. J. Phys. Chem. C 2011, 115(20), 9844–9849. [15] Darul, J.; Piszora, P. Li0.5Ni0.5Mn2O4 spinel: Its synthesis, structure and high pressure properties. J. Alloy. Compd. 2017, 722, 452–457. [16] Ohtani, S.; Watanabe, Y.; Saito, M.; Abe, N.; Taniguchi, K.; Sagayama, H.; Arima, T.; Watanabe, M.; Noda, Y. Orbital dilution effect in ferrimagnetic Fe1-xMnxCr2O4: competition between anharmonic lattice potential and spin–orbit coupling. J. Phys.-Condens. Mat. 2010, 22(17), 176003.


29


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[17] Ikuhara, Y. H.; Gao, X.; Huang, R.; Fisher, C. A.; Kuwabara, A.; Moriwake, H.; Kohama, K. Epitaxial Growth of LiMn2O4 Thin Films by Chemical Solution Deposition for Multilayer Lithium-Ion Batteries. J. Phys. Chem. C 2014, 118(34), 19540–19547. [18] Abdollahifar, M.; Huang, S. S.; Lin, Y. H.; Sheu, H. S.; Lee, J. F.; Lu, M. L.; Liao Y. F.; Wu, N. L. Tetragonal LiMn2O4 as dual-functional pseudocapacitor-battery electrode in aqueous Li-ion electrolytes. J. Power Sources 2019, 412, 545-551. [19] Yildiz, B. “Stretching” the energy landscape of oxides - Effects on electrocatalysis and diffusion. MRS Bull. 2014, 39(2), 147-156. [20] Fauth, F.; Peral, I.; Popescu, C.; Knapp, M. The new material science powder diffraction beamline at ALBA synchrotron. Powder Diffr. 2013, 28(S2), S360-S370. [21] Fei Y, Ricolleau A, Frank M, Mibe K, Shen G., Prakapenka V. Toward an internally consistent pressure scale. Proc. Natl. Acad. Sci. U. S. A. 2007, 104, 9182-9186. [22] Klotz, S.; Chervin, J. C.; Munsch, P.; Le Marchand, G. Hydrostatic limits of 11 pressure transmitting media. J. Phys. D: Appl. Phys. 2009, 42, 075413 1-7. [23] Hammersley, A. P.; Svensson, S. O.; Hanfland, M.; Fitch A. N.; Hausermann, D. Twodimensional detector software: from real detector to idealised image or two-theta scan. High Pressure Res. 1996, 14, 235-248. [24] Larson, A. C.; Von Dreele, R. B. GSAS General Structure Analysis System, Report LAUR 86-748. Los Alamos National Laboratory, Los Alamos, NM 1986. [25] Toby, B. H. EXPGUI, a graphical user interface for GSAS. J. Appl. Cryst. 2001, 34(2), 210-213.


30

Page 31 of 33 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


[26] Angel, R. J.; Gonzales-Platas, J.; Alvaro, M. EosFit7c and a Fortran module (library) for equation of state calculations Z. Kristallogr. - Cryst. Mater. 2014, 229, 405–419. [27] Gonzalez-Platas, J.; Alvaro, M.; Nestola, F.; Angel, R. J. EosFit7-GUI: a new graphical user interface for equation of state calculations, analyses and teaching computer programs. J. Appl. Crystallogr. 2016, 49, 1377-1382. [28] Reehuis, M.; Tovar, M.; Többens, D. M.; Pattison, P.; Hoser, A.; Lake, B. Competing Jahn–Teller distortions and ferrimagnetic ordering in the geometrically frustrated system Ni1xCuxCr2O4.

Phys. Rev. B 2015, 91(2), 024407.

[29] Åsbrink, S.; Waśkowska, A.; Olsen, J. S.; Gerward, L. High-pressure phase of the cubic spinel NiMn2O4. Phys. Rev. B 1998, 57(9), 4972. [30] Erradonea, D.; Munoz, A.; Gonzalez-Platas, J. Comment on “High-pressure x-ray diffraction study of YBO3/Eu3+, GdBO3, ad EuBO3: Pressure-induced amorphization in GdBO3”. J. Appl. Phys. 2014, 115, 216101. [31] He, D.; Shieh, S.R., Duffy, T. Strength and equation of state of boron suboxide from radial x-ray diffraction in a diamond cell under nonhydrostatic compression. Phys. Rev. B 2004, 70, 184121. [32] Piszora, P. In-situ investigations of LiMn2O4 at high pressure. Z. Kristallogr. S 2007, 26, 387–392. [33] Darul, J.; Nowicki, W.; Piszora, P. Unusual compressional behavior of lithium– manganese oxides: a case study of Li4Mn5O12. J. Phys. Chem. C 2012, 116(33), 17872–17879.


31


Page 32 of 33

[34] Araujo, L. R.; Gallington, L. C.; Wilkinson, A. P.; Evans, J. S. Phase behaviour, thermal expansion and compressibility of SnMo2O8. J. Solid State Chem. 2018, 258, 885–893. [35] Takemura, K. Absence of the c/a anomaly in Zn under high pressure with a heliumpressure medium. Phys. Rev. B 1999, 60(9), 6171. [36] Wang, X.; Chen, C.; Huang, X.; Wang, J.; Yao, M.; Wang, K.; Huang, F.; Han, B.; Zhou, Q.; Li, F. Acoustic and elastic properties of silicone oil under high pressure. RSC Adv. 2015, 5(48), 38056–38060. [37] Robinson, K.; Gibbs, G. V.; Ribbe, P. H. Quadratic elongation: a quantitative measure of distortion in coordination polyhedra. Science 1971, 172(3983), 567–570.


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Insights into Polymorphism of Lithium Manganese ... - ACS Publications

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