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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

RbB 3 Si 3 : An Alkali Metal Borosilicide that is Metastable and Superconducting at 1 atm

The stability, electronic structure and potential superconductivity in AB 3 Si 3 (A = Na, K, Rb, and Cs) compounds that assume the clathrate-based sodalite structure whose frameworks consists of covalent B-Si bonds is investigated via first-principles calculations. This structure type has recently been predicted in a number of high temperature superconducting hydrides, but these are only stable under megabar pressures. Herein, we predict a novel superconducting phase, RbB 3 Si 3 , that could be synthesized under pressures that are a factor of ten smaller, ~10 GPa, and quenched to atmospheric conditions. Electron-phonon coupling calculations predict that RbB 3 Si 3 possesses a superconducting critical temperature, T c , of 14 K at 1 atm. Here, the dynamic stability of RbB 3 Si 3 and CsB 3 Si 3 at ambient pressure can be explained by considering the chemical pressure exerted on the B-Si framework that is caused by the size effect of the alkali metal atom.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Electrical Properties of Carbon Dioxide Hydrate: Implications for Monitoring CO 2 in the Gas Hydrate Stability Zone

CO 2 and CH 4 clathrate hydrates are of keen interest for energy and carbon cycle considerations. While both typically form on Earth as cubic structure I (sI), we find that pure CO 2 hydrate exhibits over an order of magnitude higher electrical conductivity ( σ ) than pure CH 4 hydrate at geologically relevant temperatures. In this study, the conductivity was obtained from frequency-dependent impedance ( Z ) measurements made on polycrystalline CO 2 hydrate (CO 2 ·6.0 ± 0.2H 2 O by methods here) with 25% gas-filled porosity, compared with CH 4 hydrate (CH 4 ·5.9H 2 O) formed and measured in the same apparatus and exhibiting closely matching grain characteristics. The conductivity of CO 2 hydrate is 6.5 × 10 –4 S/m at 273K with an activation energy ( E a ) of 46.5 kJ/mol at 260–281 K, compared with ~5 × 10 –5 S/m and 34.8 kJ/m for CH 4 hydrate. Equivalent circuit modeling indicates that different pathways govern conduction in CO 2 versus CH 4 hydrate. Results show promise for use of electromagnetic methods in monitoring CO 2 hydrate formation in certain natural settings or in CO 2 /CH 4 exchange efforts.

58 GEOSCIENCES↗
DOE OSTI2025

X-ray-diffraction and electrical-transport imaging of superconducting superhydride (La,Y)H 10

Understanding how microscopic structural domains govern macroscopic electronic properties is central to advancing hydride superconductors, yet such correlations remain poorly resolved under pressure. We report the synthesis and characterization of (La 0.9 Y 0.1 )H 10 superhydrides exhibiting coexisting cubic $Fm\bar{3}m$ and $P6_3/mmc$ hexagonal clathrate phases observed over the pressure range from 168 GPa down to 136 GPa. Using synchrotron-based X-ray diffraction imaging at the upgraded Advanced Photon Source, we spatially resolved μm-scale distributions of these phases, revealing structural inhomogeneity across the sample. Four-probe resistance measurements confirmed superconductivity with two distinct transitions: an onset at 244 K associated with the cubic phase and a second near 220 K linked to the hexagonal phase. Notably, resistance profiles collected from multiple current and voltage permutations showed variations in transition width and onset temperature that correlated with the spatial phase distribution. These findings demonstrate a direct connection between local structural domains and superconducting behavior.

Materials science↗
DOE OSTI2020

Gapped metals as thermoelectric materials revealed by high-throughput screening

The typical strategy to design high performance thermoelectric materials is to dope a semiconducting material until optimal properties are obtained. However, some known thermoelectric materials such as La 3 Te 4 , Mo 3 Sb 7 , Yb 14 MnSb 11 , and NbCoSb are actually gapped metals,i.e., their band structure displays a gap slightly above or below the band crossed by the Fermi level. This key feature makes these metals comparable to degenerate semiconductors and thus suitable for thermoelectric applications. In this work, we perform a computational high-throughput search for such gapped metals exhibiting attractive thermoelectric properties. Several thousands of metals are found to present this key feature, and about one thousand of them show decent thermoelectric properties as evaluated by a computed zT. We present the different chemistry of gapped metals we discovered such as clathrates, Chevrel phases, or transition metal dichalcogenides and discuss their previous studies as thermoelectric and their potential as new thermoelectric materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Structural investigation of three distinct amorphous forms of Ar hydrate

Three amorphous forms of Ar clathrate hydrate (pressure-amorphized, annealed and recovered) were characterized by isotope substitution ( 36 Ar) neutron diffraction and molecular dynamics and their local coordinations analyzed and compared to pure ice.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Superconductivity in La and Y hydrides: Remaining questions to experiment and theory

Recent reports of the superconductivity in hydrides of two different families (covalent lattice, as in SH3 and clathrate-type H-cages containing La and Y atoms, as in LaH10 and YH6) have revealed new families of high-Tc materials with Tc’s near room temperature values. These findings confirm earlier expectations that hydrides may have very high Tc’s due to the fact that light H atoms have very high vibrational frequencies, leading to high Tc values within the conventional Bardeen–Cooper–Schrieffer phonon mechanism of superconductivity. However, as is pointed out by Ashcroft, it is important to have the metallic hydrogen “alloyed” with the elements added to it. This concept of a metallic alloy containing a high concentration of metal-like hydrogen atoms has been instrumental in finding new high-Tc superhydrides. These new superhydride “room-temperature” superconductors are stabilized only at very high pressures above 100 GPa, making the experimental search for their superconducting properties very difficult. We will review the current experimental and theoretical results for LaH10−x and YH6−x superhydrides.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Tuning chemical precompression: Theoretical design and crystal chemistry of novel hydrides in the quest for warm and light superconductivity at ambient pressures

Over the past decade, a combination of crystal structure prediction techniques and experimental synthetic work has thoroughly explored the phase diagrams of binary hydrides under pressure. The fruitfulness of this dual approach is demonstrated in the recent identification of several superconducting hydrides with T c s approaching room temperature. We start with an overview of the computational procedures for predicting stable structures and estimating their propensity for superconductivity. A survey of phases with high T c reveals some common structural features that appear conducive to the strong coupling of the electronic structure with atomic vibrations that leads to superconductivity. We discuss the stability and superconducting properties of phases containing two of these—molecular H 2 units mixed with atomic H and hydrogenic clathrate-like cages—as well as more unique motifs. Lastly, we argue that ternary hydride phases, whose exploration is still in its infancy, are a promising route to achieve simultaneous superconductivity at high temperatures and stability at low pressures. Several ternary hydrides arise from the addition of a third element to a known binary hydride structure through site mixing or onto a new site, and several more are based on altogether new structural motifs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Effective optimization of atomic decoration in giant and superstructurally ordered crystals with machine learning

Crystals with complicated geometry are often observed with mixed chemical occupancy among Wyckoff sites, presenting a unique challenge for accurate atomic modeling. Similar systems possessing exact occupancy on all the sites can exhibit superstructural ordering, dramatically inflating the unit cell size. In this work, a crystal graph convolutional neural network (CGCNN) is used to predict optimal atomic decorations on fixed crystalline geometries. This is achieved with a site permutation search (SPS) optimization algorithm based on Monte Carlo moves combined with simulated annealing and basin-hopping techniques. Our approach relies on the evidence that, for a given chemical composition, a CGCNN estimates the correct energetic ordering of different atomic decorations, as predicted by electronic structure calculations. This provides a suitable energy landscape that can be optimized according to site occupation, allowing the prediction of chemical decoration in crystals exhibiting mixed or disordered occupancy, or superstructural ordering. Verification of the procedure is carried out on several known compounds, including the superstructurally ordered clathrate compound Rb8Ga27Sb16 and vacancy-ordered perovskite Cs2SnI6, neither of which was previously seen during the neural network training. In addition, the critical temperature of an order–disorder phase transition in solid solution CuZn is probed with our SPS routines by sampling site configuration trajectories in the canonical ensemble. This strategy provides an accurate method for determining favorable decoration in complex crystals and analyzing site occupation at unprecedented speed and scale.

Chemistry↗
DOE OSTI2020

High-temperature superconductivity in LaH 10

The recent discovery of a high critical temperature $T_c$ in compressed H 3 S has been followed by the prediction of Liu et al. of $T_c$ ≈ 250 K in the clathrate LaH 10 structure. This report has been confirmed experimentally by Somayazulu et al. and Drozdov et al. Additional theoretical work by Wang et al. and Quan et al. further established the mechanism of electron-phonon interaction and the dominant role of hydrogen. In the present Rapid Communication we follow the classic McMillan paper, which separates the electron and phonon contributions to the electron-phonon coupling λ. We first compute the numerator of McMillan's expression, the Hopfield parameter η, using the theory of Gaspari and Gyorffy (GG), and obtain the force constants in the denominator from Wang et al. and Quan et al. The resulting λ is used in the Allen-Dynes equation to calculate $T_c$. The value of $T_c$ reaches a maximum in the range of 236–263 K at pressures of 255 GPa and decreases for smaller or larger pressures. Further, we provide a thorough analysis of the different terms of the GG equation and draw the conclusion that the $\textit{sp}$ channel of the hydrogen is the most important contribution to obtain high values of $T_c$ in this material. Consistent with Wang et al., we find large values of λ that decrease with increasing pressure. In addition, we find that the hydrogen sites are the largest contributors to the total value of the coupling constant λ. That is, the acoustic mode associated with La contributes only 2% to the total λ, while the optic modes associated with H contribute 18% for the H1 site and 80% for the H2 site. These relative contributions to λ are consistent with those given by Wang et al. and by Quan et al. Thus, our results strongly support the view that LaH 10 is a metallic hydrogen superconductor.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Room-temperature superconductivity in boron- and nitrogen-doped lanthanum superhydride

Recent theoretical and experimental studies of hydrogen-rich materials at megabar pressures (i.e., >100 GPa) have led to the discovery of very high-temperature superconductivity in these materials. Lanthanum superhydride LaH10 has been of particular focus as the first material to exhibit a superconducting critical temperature (T c ) near room temperature. Experiments indicate that the use of ammonia borane as the hydrogen source can increase the conductivity onset temperatures of lanthanum superhydride to as high as 290 K. In this work, we examine the doping effects of B and N atoms on the superconductivity of LaH 10 in its fcc ($Fm\bar{3}m$) clathrate structure at megabar pressures. Doping at H atomic positions strengthens the H 32 cages of the structure to give higher phonon frequencies that enhance the Debye frequency and thus the calculated T c . The predicted T c can reach 288 K in LaH 9.985 N 0.015 within the average high-symmetry structure at 240 GPa. The remarkably large shift in T c to higher values produced by small degrees of chemical doping opens the prospect for the creation of still higher-temperature superconductivity in superhydrides potentially at even lower-pressure conditions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Solvent organization in the ultrahigh-resolution crystal structure of crambin at room temperature

Ultrahigh-resolution structures provide unprecedented details about protein dynamics, hydrogen bonding and solvent networks. The reported 0.70 Å, room-temperature crystal structure of crambin is the highest-resolution ambient-temperature structure of a protein achieved to date. Sufficient data were collected to enable unrestrained refinement of the protein and associated solvent networks using SHELXL . Dynamic solvent networks resulting from alternative side-chain conformations and shifts in water positions are revealed, demonstrating that polypeptide flexibility and formation of clathrate-type structures at hydrophobic surfaces are the key features endowing crambin crystals with extraordinary diffraction power.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Materials Data on Li4Cu(PO4)2 by Materials Project

Li4Cu(PO4)2 is Clathrate-derived structured and crystallizes in the monoclinic Pc space group. The structure is three-dimensional. there are four inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with two equivalent LiO4 tetrahedra, corners with two equivalent CuO4 tetrahedra, corners with four PO4 tetrahedra, and an edgeedge with one LiO4 tetrahedra. There are a spread of Li–O bond distances ranging from 1.88–2.02 Å. In the second Li1+ site, Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with two equivalent LiO4 tetrahedra, corners with two equivalent CuO4 tetrahedra, corners with four PO4 tetrahedra, and edges with two LiO4 tetrahedra. There are a spread of Li–O bond distances ranging from 1.99–2.09 Å. In the third Li1+ site, Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with four LiO4 tetrahedra, corners with four PO4 tetrahedra, and an edgeedge with one LiO4 tetrahedra. There are a spread of Li–O bond distances ranging from 1.90–2.04 Å. In the fourth Li1+ site, Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with two equivalent CuO4 tetrahedra, corners with four LiO4 tetrahedra, and corners with four PO4 tetrahedra. There are a spread of Li–O bond distances ranging from 1.95–2.06 Å. Cu2+ is bonded to four O2- atoms to form CuO4 tetrahedra that share corners with four PO4 tetrahedra and corners with six LiO4 tetrahedra. There are a spread of Cu–O bond distances ranging from 1.91–2.14 Å. There are two inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent CuO4 tetrahedra and corners with eight LiO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.52–1.60 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent CuO4 tetrahedra and corners with eight LiO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.53–1.58 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to one Li1+, one Cu2+, and one P5+ atom. In the second O2- site, O2- is bonded in a trigonal non-coplanar geometry to one Li1+, one Cu2+, and one P5+ atom. In the third O2- site, O2- is bonded to two Li1+, one Cu2+, and one P5+ atom to form OLi2CuP tetrahedra that share corners with four OLi2CuP tetrahedra and an edgeedge with one OLi3P trigonal pyramid. In the fourth O2- site, O2- is bonded in a trigonal planar geometry to two Li1+ and one P5+ atom. In the fifth O2- site, O2- is bonded to two Li1+, one Cu2+, and one P5+ atom to form distorted OLi2CuP tetrahedra that share corners with four OLi2CuP tetrahedra and corners with two equivalent OLi3P trigonal pyramids. In the sixth O2- site, O2- is bonded to three Li1+ and one P5+ atom to form distorted OLi3P tetrahedra that share corners with four OLi2CuP tetrahedra and an edgeedge with one OLi3P trigonal pyramid. In the seventh O2- site, O2- is bonded in a trigonal planar geometry to two Li1+ and one P5+ atom. In the eighth O2- site, O2- is bonded to three Li1+ and one P5+ atom to form a mixture of distorted corner and edge-sharing OLi3P trigonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Li2TeO3 by Materials Project

Li2TeO3 is Clathrate-derived structured and crystallizes in the monoclinic C2/c space group. The structure is two-dimensional and consists of two Li2TeO3 sheets oriented in the (0, 0, 1) direction. there are two inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded to four O2- atoms to form a mixture of edge and corner-sharing LiO4 tetrahedra. There are a spread of Li–O bond distances ranging from 1.96–2.04 Å. In the second Li1+ site, Li1+ is bonded to four O2- atoms to form a mixture of edge and corner-sharing LiO4 tetrahedra. There are a spread of Li–O bond distances ranging from 1.95–2.03 Å. Te4+ is bonded in a trigonal non-coplanar geometry to three O2- atoms. There is one shorter (1.88 Å) and two longer (1.89 Å) Te–O bond length. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two Li1+ and one Te4+ atom. In the second O2- site, O2- is bonded to three Li1+ and one Te4+ atom to form distorted edge-sharing OLi3Te trigonal pyramids. In the third O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Li1+ and one Te4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Li4P2O7 by Materials Project

Li4P2O7 is Clathrate-derived structured and crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are four inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with three LiO4 tetrahedra, corners with four PO4 tetrahedra, and edges with two LiO4 tetrahedra. There are a spread of Li–O bond distances ranging from 1.91–2.01 Å. In the second Li1+ site, Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with four LiO4 tetrahedra, corners with four PO4 tetrahedra, and an edgeedge with one LiO4 tetrahedra. There are a spread of Li–O bond distances ranging from 1.95–2.04 Å. In the third Li1+ site, Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with four PO4 tetrahedra, corners with five LiO4 tetrahedra, and an edgeedge with one LiO4 tetrahedra. There are a spread of Li–O bond distances ranging from 1.96–2.04 Å. In the fourth Li1+ site, Li1+ is bonded to four O2- atoms to form distorted LiO4 tetrahedra that share corners with two equivalent LiO4 tetrahedra, corners with three equivalent PO4 tetrahedra, an edgeedge with one LiO4 tetrahedra, and an edgeedge with one PO4 tetrahedra. There are a spread of Li–O bond distances ranging from 1.91–2.10 Å. There are two inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one PO4 tetrahedra and corners with eight LiO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.52–1.65 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one PO4 tetrahedra, corners with seven LiO4 tetrahedra, and an edgeedge with one LiO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.52–1.65 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a trigonal planar geometry to two Li1+ and one P5+ atom. In the second O2- site, O2- is bonded to three Li1+ and one P5+ atom to form distorted corner-sharing OLi3P trigonal pyramids. In the third O2- site, O2- is bonded to three Li1+ and one P5+ atom to form a mixture of distorted corner and edge-sharing OLi3P trigonal pyramids. In the fourth O2- site, O2- is bonded in a trigonal planar geometry to two Li1+ and one P5+ atom. In the fifth O2- site, O2- is bonded in a distorted T-shaped geometry to two Li1+ and one P5+ atom. In the sixth O2- site, O2- is bonded to three Li1+ and one P5+ atom to form a mixture of corner and edge-sharing OLi3P tetrahedra. In the seventh O2- site, O2- is bonded in a distorted T-shaped geometry to one Li1+ and two P5+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cd4Sb2I3 by Materials Project

Cd4Sb2I3 is Clathrate-derived structured and crystallizes in the cubic Pa-3 space group. The structure is three-dimensional. there are two inequivalent Cd2+ sites. In the first Cd2+ site, Cd2+ is bonded in a rectangular see-saw-like geometry to two Sb+2.50- and two equivalent I1- atoms. There are one shorter (2.79 Å) and one longer (2.80 Å) Cd–Sb bond lengths. There are one shorter (3.05 Å) and one longer (3.17 Å) Cd–I bond lengths. In the second Cd2+ site, Cd2+ is bonded in a rectangular see-saw-like geometry to one Sb+2.50- and three equivalent I1- atoms. The Cd–Sb bond length is 2.78 Å. All Cd–I bond lengths are 2.99 Å. There are two inequivalent Sb+2.50- sites. In the first Sb+2.50- site, Sb+2.50- is bonded to four Cd2+ atoms to form corner-sharing SbCd4 trigonal pyramids. In the second Sb+2.50- site, Sb+2.50- is bonded to three equivalent Cd2+ and one Sb+2.50- atom to form distorted corner-sharing SbCd3Sb tetrahedra. The Sb–Sb bond length is 2.83 Å. I1- is bonded in a trigonal non-coplanar geometry to three Cd2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cd4P2Cl3 by Materials Project

Cd4P2Cl3 is Clathrate-derived structured and crystallizes in the cubic Pa-3 space group. The structure is three-dimensional. there are two inequivalent Cd2+ sites. In the first Cd2+ site, Cd2+ is bonded in a rectangular see-saw-like geometry to one P+2.50- and three equivalent Cl1- atoms. The Cd–P bond length is 2.50 Å. All Cd–Cl bond lengths are 2.65 Å. In the second Cd2+ site, Cd2+ is bonded in a distorted rectangular see-saw-like geometry to two P+2.50- and two equivalent Cl1- atoms. There are one shorter (2.50 Å) and one longer (2.53 Å) Cd–P bond lengths. There are one shorter (2.75 Å) and one longer (2.85 Å) Cd–Cl bond lengths. There are two inequivalent P+2.50- sites. In the first P+2.50- site, P+2.50- is bonded to three equivalent Cd2+ and one P+2.50- atom to form corner-sharing PCd3P tetrahedra. The P–P bond length is 2.20 Å. In the second P+2.50- site, P+2.50- is bonded to four Cd2+ atoms to form corner-sharing PCd4 trigonal pyramids. Cl1- is bonded in a trigonal non-coplanar geometry to three Cd2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Li2CO3 by Materials Project

Li2CO3 is Clathrate-derived structured and crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Li1+ is bonded to four O2- atoms to form a mixture of corner and edge-sharing LiO4 tetrahedra. There are a spread of Li–O bond distances ranging from 1.92–2.04 Å. C4+ is bonded in a trigonal planar geometry to three O2- atoms. There is one shorter (1.29 Å) and two longer (1.31 Å) C–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a trigonal planar geometry to two equivalent Li1+ and one C4+ atom. In the second O2- site, O2- is bonded to three equivalent Li1+ and one C4+ atom to form a mixture of distorted corner and edge-sharing OLi3C tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Li4Fe(PO4)2 by Materials Project

Li4Fe(PO4)2 is Clathrate-derived structured and crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are four inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with four LiO4 tetrahedra, corners with four PO4 tetrahedra, and edges with two LiO4 tetrahedra. There are a spread of Li–O bond distances ranging from 2.00–2.08 Å. In the second Li1+ site, Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with four PO4 tetrahedra, corners with six LiO4 tetrahedra, and an edgeedge with one LiO4 tetrahedra. There are a spread of Li–O bond distances ranging from 1.99–2.07 Å. In the third Li1+ site, Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with two equivalent LiO4 tetrahedra, corners with two equivalent FeO4 tetrahedra, corners with four PO4 tetrahedra, and an edgeedge with one LiO4 tetrahedra. There are a spread of Li–O bond distances ranging from 1.98–2.09 Å. In the fourth Li1+ site, Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with two equivalent FeO4 tetrahedra, corners with four LiO4 tetrahedra, and corners with four PO4 tetrahedra. There are a spread of Li–O bond distances ranging from 1.94–2.00 Å. Fe2+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with four LiO4 tetrahedra and corners with four PO4 tetrahedra. There are two shorter (2.02 Å) and two longer (2.03 Å) Fe–O bond lengths. There are two inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent FeO4 tetrahedra and corners with eight LiO4 tetrahedra. There is two shorter (1.55 Å) and two longer (1.56 Å) P–O bond length. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent FeO4 tetrahedra and corners with eight LiO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.55–1.57 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded to three Li1+ and one P5+ atom to form a mixture of distorted corner and edge-sharing OLi3P trigonal pyramids. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to one Li1+, one Fe2+, and one P5+ atom. In the third O2- site, O2- is bonded to three Li1+ and one P5+ atom to form a mixture of distorted corner and edge-sharing OLi3P tetrahedra. In the fourth O2- site, O2- is bonded to three Li1+ and one P5+ atom to form a mixture of corner and edge-sharing OLi3P tetrahedra. In the fifth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Li1+, one Fe2+, and one P5+ atom. In the sixth O2- site, O2- is bonded in a trigonal planar geometry to one Li1+, one Fe2+, and one P5+ atom. In the seventh O2- site, O2- is bonded to three Li1+ and one P5+ atom to form corner-sharing OLi3P tetrahedra. In the eighth O2- site, O2- is bonded in a trigonal planar geometry to one Li1+, one Fe2+, and one P5+ atom.

36 MATERIALS SCIENCE↗