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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

(NH 3 (CH 2 ) 7 NH 3 ) 2 Sn 3 I 10 , a Vacancy-Ordered Three-Dimensional Tin(II) Perovskite-Derived Semiconductor

Ordering vacancies in hybrid Sn(II) halide semiconductors provides a strategy for preventing uncontrolled oxidation and formation of mobile holes. In this study, we report the structure and optical and electronic properties of (NH 3 (CH 2 ) 7 NH 3 ) 2 Sn 3 I 10 , a vacancy-ordered perovskite derivative with three-dimensional inorganic connectivity. The crystal structure resembles that of a Dion–Jacobson layered perovskite derivative, but with [SnI 5 ] square pyramids bridging the layers. UV–vis diffuse reflectance spectroscopy reveals a sharp onset of light absorption at 1.86(1) eV with the photoluminescence emission maximum at 1.90(1) eV. However, the maximum excitation occurs from 3.42 to 3.81 eV (325 to 370 nm), revealing a significant Stokes shift of 1.3 eV. The electronic properties determined from dark and time-resolved microwave conductivity measurements reveal a minimum carrier mobility of 4.3 × 10 –2 cm 2 V –1 s –1 and a maximum carrier density of 5.96 × 10 16 cm –3 , a uniquely low value for a hybrid Sn(II) halide semiconductor. The transport behavior in combination with first-principles calculations of the electronic band structure and dielectric permittivity suggest polaron-mediated electronic transport, yet the photogenerated carriers have a fast and fluence-dependent nonradiative recombination rate, suggestive of localized “defect-like” states at the band edge. The observed photoluminescence is most consistent with single-ion-like behavior of an asymmetric Sn(II) environment. Together, these results suggest that defect ordering presents a strategy for the reduction of mobile charge carriers at equilibrium.

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

Perovskite-Derivative Valleytronics

Halide perovskites are revolutionizing the renewable energy sector owing to their high photovoltaic efficiency, low manufacturing cost, and flexibility. Their remarkable mobility and long carrier lifetime are also valuable for information technology, but fundamental challenges like poor stability under an electric field prevent realistic applications of halide perovskites in electronics. Here, it is discovered that valleytronics is a promising route to leverage the advantages of halide perovskites and derivatives for information storage and processing. The synthesized all-inorganic lead-free perovskite derivative, Cs 3 Bi 2 I 9 , exhibits strong light-matter interaction and parity-dependent optically addressable valley degree of freedom. In this work, robust optical helicity in all odd-layer-number crystals with inversion symmetry breaking is observed, indicating excitonic coherence extending well beyond 11 layers. The excellent optical and valley properties of Cs 3 Bi 2 I 9 arise from the unique parallel bands, according to first principles calculations. This discovery points to new materials design principles for scalable valleytronic devices and demonstrates the promise of perovskite derivatives beyond energy applications.

2D materials↗
DOE OSTI2021

Perovskite-Derived Cs 2 SnCl 6 –Silica Composites as Advanced Waste Forms for Chloride Salt Wastes

Advanced materials and processes are required to separate halides and fission products from complex salt waste streams associated with the chemical reprocessing of used nuclear fuels and molten salt reactor technologies for immobilization into chemically durable waste forms. Here, in this work, we explore an innovative concept using metal-halide perovskites as advanced host phases to incorporate Cs and Cl with very high waste loadings. Wet chemistry-synthesized Cs 2 SnCl 6 powders from CsCl salt solutions are successfully encapsulated into a silica matrix to form a composite using low-temperature spark plasma sintering with tunable Cs and Cl loadings up to 31 wt.% and 26 wt.%, respectively. Chemical durability testing of the composite waste forms by semi-dynamic leaching experiments demonstrates that incongruent leaching mechanism dominated. The metal-halide perovskite-silica composite waste forms display exceptional chemical durability with the long-term release rates of Cs and Cl comparable to or outperforming the state-of-the-art waste form materials but with significantly higher waste loadings. The scalable synthesis of the metal-halide perovskite from wet-chemistry processes opens up new opportunities in designing perovskite-glass composite waste forms for salt wastes with very high waste loadings and exceptional chemical durability for the sustainable development of advanced fuel cycles and next-generation reactor technologies.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2024

Strong interlayer coupling and long-lived interlayer excitons in two-dimensional perovskite derivatives and transition metal dichalcogenides van der Waals heterostructures

Two-dimensional (2D) van der Waals (vdW) heterostructures offer new platforms for exploring novel physics and diverse applications ranging from electronics and photonics to optoelectronics at the nanoscale. The studies to date have largely focused on transition-metal dichalcogenides (TMDCs) based samples prepared by mechanical exfoliation method, therefore it is of signi ficant interests to study high-quality vdW heterostructures using novel materials prepared by a versatile method. Here, we report a two-step vapor phase growth process for the creation of high-quality vdW heterostructures based on perovskites and TMDCs, such as 2D Cs 3 Bi 2 I 9 /MoSe 2 , with a large lattice mismatch. Supported by experimental and theoretical investigations, we discover that the Cs 3 Bi 2 I 9 /MoSe 2 vdW heterostructure possesses hybrid band alignments consisting of type -I and type-II heterojunctions because of the existence of defect energy levels in Cs 3 Bi 2 I 9 . More importantly, we demonstrate that the type-II heterojunction in the Cs 3 Bi 2 I 9 /MoSe 2 vdW heterostructure not only shows a higher interlayer exciton density, but also exhibits a longer interlayer exciton lifetime than traditional 2D TMDCs based type-II heterostructures. We attribute this phenomenon to the reduced overlap of electron and hole wavefunctions caused by the large lattice mismatch. Finally, our work demonstrates that it is possible to directly grow high-quality vdW heterostructures based on entirely different materials which provide promising platforms for exploring novel physics and cutting-edge applications, such as optoelectronics, valleytronics, and high-temperature super fluidity.

36 MATERIALS SCIENCE↗
DOE OSTI2024

I – /I 3 – Redox-Assisted Synthesis and Properties of Low Dimensional, Mixed-Valent Gold Iodide Perovskite Derivatives

Here, we report a set of three new mixed-valent Au I Au III iodides: (ClPy) 3 [AuI 2 ] 2 [AuI 4 ] [1], (BrPy) 3 [AuI 2 ] 2 [AuI 4 ] [2], and (ClPy) 2 [AuI 2 ][AuI 4 ] [3], as well as three new monovalent Au III iodides: (XPy) 2 [AuI 4 ][I 3 ] (Py = 4-X-pyridinium X = Cl, Br, and I) [4–6]. Two of these mixed-valent compounds (1 and 2) incorporate both monovalent Au I ···Au I (aurophilic bonding) and mixed-valent Au I I···Au III I couples (Au–I halogen bonding), to the best of our knowledge an unprecedented structural feature. These same two mixed-valent compounds also exhibit a rare low-dimensional molecular architecture with respect to second sphere Au···I interactions, namely, 1D chains of Au···I interactions, extending along a single crystallographic axis. All compounds were synthesized with the assistance of the I – /I 3 – redox couple and tacit manipulation of the polyiodide content during synthesis. Air-free synthesis was used to influence the redox process of I – /I 3 – , resulting in better selection for mixed-valent products. Compounds 1–2 and 4–5 exhibit a characteristically narrow bandgap (1.04–1.25 eV), as measured via diffuse reflectance spectroscopy (DRS). Computational analyses were used to rationalize the specific assembly modes of [AuI 2 ] – and [AuI 4 ] – species, and they show that the Au I ···I interaction type is favored over the Au III ···I.

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

Structure, Morphology, and Photovoltaic Implications of Halide Alloying in Lead-Free Cs 3 Sb 2 Cl x I 9-x 2D-Layered Perovskites

Compositional tuning has been a major driving force behind the excellent optoelectronic properties observed in typical Pb-based perovskites. For lead-free perovskite derivatives, a challenge to understanding the connection between compositional tuning and intrinsic optoelectronic properties, hence a barrier towards boosting their performance, comes from the fact that multiple crystalline substructures can form based on composition, film processing, or both. Especially with lower dimensional (0D, 1D, 2D) substructures, the particular polymorph present in the film can be a greater determinant of optoelectronic properties than the composition itself. Herein, we report a simple method to alloy the halide site in all-inorganic lead-free Cs 3 Sb 2 I 9 films while maintaining a consistent 2D-layered substructure, as a means to independently study the photovoltaic implications of halide substitution. We use a broad suite of spectroscopy and device measurements to identify an optimal stoichiometric substitution of chloride for iodide (~ 8 mol%, measured) that balances both intrinsic and bulk optoelectronic properties to achieve a top power conversion efficiency of 2.2%. This work underscores the importance of controlling substructure while investigating the impacts of compositional tuning for the development of lead-free perovskites, and more broadly validates the approach towards realizing lead-free alternative perovskite solar technologies.

14 SOLAR ENERGY↗
DOE OSTI2022

Correlating Broadband Photoluminescence with Structural Dynamics in Layered Hybrid Halide Perovskites

The emission of white light from a single material is atypical and is of interest for solid-state lighting applications. Broadband light emission has been observed in some layered perovskite derivatives, A 2 PbBr 4 (A = R-NH 3 + ), and correlates with static structural distortions corresponding to out-of-plane tilting of the lead bromide octahedra. While materials with different organic cations can yield distinct out-of-plane tilts, the underlying origin of the octahedral tilting remains poorly understood. Using high energy resolution (e.g., quasi-elastic) neutron scattering, this contribution details the rotational dynamics of the organic cations in A 2 PbBr 4 materials where A = n-butylammonium (nBA), 1,8-diaminooctammonium (ODA), and 4-aminobutyric acid (GABA). The organic cation dynamics differentiate (nBA) 2 PbBr 4 from (ODA)PbBr 4 or (GABA) 2 PbBr 4 in that the larger spatial extent of dynamics of nBA yields a larger effective cation radius. The larger effective volume of the nBA cation in (nBA) 2 PbBr 4 yields a closer to ideal A-site geometry, preventing the out-of-plane tilt and broadband luminescence. In all three compounds, we observe hydrogen dynamics attributed to rotation of the ammonium headgroup and at a time scale faster than the white light photoluminescence studied by time-correlated single photon counting spectroscopy. This supports a previous assignment of the broadband emission as resulting from a single ensemble, such that the emissive excited state experiences many local structures faster than the emissive decay. Furthermore, the findings presented here highlight the role of the organic cation and its dynamics in hybrid organic–inorganic perovskites and white light emission.

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

Immobilization of cesium and iodine into Cs 3 Bi 2 I 9 perovskite-silica composites and core-shell waste forms with high waste loadings and chemical durability

Cs$_3$Bi$_2$I$_9$, a defect perovskite derivative, is a potential host phase to immobilize iodine and cesium with high waste loadings. In this work, two strategies were explored to form Cs$_3$Bi$_2$I$_9$-silica composites and a core-shell structure in order to improve chemical durability of waste form materials meanwhile maintaining high waste loadings. Cs$_3$Bi$_2$I$_9$ loadings as high as 70 wt.% were incorporated into a silica matrix to form silica-ceramic composites, and 20 wt.% Cs$_3$Bi$_2$I$_9$ was encapsulated into silica to form a core–shell structure by low temperature spark plasma sintering. Chemical durability of the composite and core-shell waste forms was evaluated by semi-dynamic leaching experiments, and Cs and I were incongruently released from waste form matrices. A BiOI alteration layer formed, acting as a passivation layer to reduce the release of radionuclides. The long-term iodine release rate was low (30 mg m$^{-2}$ day$^{-1}$) for the 70 wt.%Cs$_3$Bi$_2$I$_9$–silica composite leached in deionized water at 90 °C, which can be further reduced to 5 × 10$^{-3}$ mg m$^{-2}$ day$^{-1}$ for the 20 wt.% core-shell structure. This work highlights a robust way to immobilize the highly mobile radionuclides with high waste loadings through encapsulation into durable matrices and a surface passivating mechanism that can greatly reduce the elemental transport from waste form materials and significantly enhance their chemical durability.

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

Multisublattice cluster expansion study of short-range ordering in iron-substituted strontium titanate

Owing to the challenges in obtaining realistic atomic configurations in large chemical phase spaces, it is not straightforward to describe structure–property relations in materials exhibiting configurational disorder. One example is iron-substituted strontium titanate (SrTi 1–x Fe x O 3–d , STF), a promising perovskite-derivative cathode material in solid oxide fuel cells that exhibits full solid solubility 0 ≤ x ≤ 1 and a tendency to exhibit short-range order. Here we demonstrate a multisublattice cluster expansion (CE) framework and apply it to STF across the full composition range. The CE approach is distinct from more traditional CE formulations in that clusters are defined explicitly by the chemical species distributed among multiple sublattices, rather than via cluster functions of occupation variables with decoration. The modified CE approach makes it easy to distinguish meaningful chemical interactions that are harder to extract from conventional CE, since for the latter chemical identity in a cluster is expressed as a product of site occupations. The least absolute shrinkage and selection operator (LASSO) is implemented as a regression analysis tool to select key clusters and avoid overfitting. We demonstrate this formulation on STF, and show that it can accurately predict configurational energies in comparison to conventional CE. From the key clusters, we identify that short-range ordering between substitutional Fe and oxygen vacancies (V O ) results in the formation of Fe–VO strings. In addition, we consider the stability of STF through CE-based Monte Carlo (MC) simulations and confirm the presence of superstructures that were previously observed in transmission electron microscopy. In this work, analysis of atomic configurations from MC samples reveals variations in the oxidation state of Fe atoms, which can be explained by the ordering tendency of Fe and V O . The cluster description and selection formalism described here may be applied to other disordered multisublattice systems for accurate and efficient material modeling.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ba3CaBi2O9 by Materials Project

Ba3CaBi2O9 is (Cubic) Perovskite-derived structured and crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. there are two inequivalent Ba2+ sites. In the first Ba2+ site, Ba2+ is bonded to twelve O2- atoms to form BaO12 cuboctahedra that share corners with twelve BaO12 cuboctahedra, faces with six BaO12 cuboctahedra, faces with two equivalent CaO6 octahedra, and faces with six BiO6 octahedra. There are a spread of Ba–O bond distances ranging from 2.99–3.12 Å. In the second Ba2+ site, Ba2+ is bonded to twelve O2- atoms to form BaO12 cuboctahedra that share corners with twelve BaO12 cuboctahedra, faces with six BaO12 cuboctahedra, faces with three equivalent CaO6 octahedra, and faces with five BiO6 octahedra. There are a spread of Ba–O bond distances ranging from 3.05–3.14 Å. Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with six BiO6 octahedra and faces with eight BaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–6°. There are four shorter (2.27 Å) and two longer (2.28 Å) Ca–O bond lengths. There are three inequivalent Bi5+ sites. In the first Bi5+ site, Bi5+ is bonded to six O2- atoms to form BiO6 octahedra that share corners with two equivalent BiO6 octahedra, corners with four equivalent CaO6 octahedra, and faces with eight BaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.09 Å) and two longer (2.22 Å) Bi–O bond lengths. In the second Bi5+ site, Bi5+ is bonded to six O2- atoms to form BiO6 octahedra that share corners with two equivalent BiO6 octahedra, corners with four equivalent CaO6 octahedra, and faces with eight BaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 1–6°. There are a spread of Bi–O bond distances ranging from 2.08–2.24 Å. In the third Bi5+ site, Bi5+ is bonded to six O2- atoms to form BiO6 octahedra that share corners with six BiO6 octahedra and faces with eight BaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–1°. There are two shorter (2.13 Å) and four longer (2.14 Å) Bi–O bond lengths. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted linear geometry to four Ba2+ and two Bi5+ atoms. In the second O2- site, O2- is bonded in a distorted linear geometry to four Ba2+, one Ca2+, and one Bi5+ atom. In the third O2- site, O2- is bonded in a distorted linear geometry to four Ba2+ and two Bi5+ atoms. In the fourth O2- site, O2- is bonded in a distorted linear geometry to four equivalent Ba2+, one Ca2+, and one Bi5+ atom. In the fifth O2- site, O2- is bonded in a distorted linear geometry to four Ba2+, one Ca2+, and one Bi5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CoRe(PbO3)2 by Materials Project

ReCo(PbO3)2 is (Cubic) Perovskite-derived structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Re6+ is bonded to six equivalent O2- atoms to form ReO6 octahedra that share corners with six equivalent CoO6 octahedra and faces with eight equivalent PbO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All Re–O bond lengths are 1.92 Å. Co2+ is bonded to six equivalent O2- atoms to form CoO6 octahedra that share corners with six equivalent ReO6 octahedra and faces with eight equivalent PbO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All Co–O bond lengths are 2.10 Å. Pb2+ is bonded to twelve equivalent O2- atoms to form PbO12 cuboctahedra that share corners with twelve equivalent PbO12 cuboctahedra, faces with six equivalent PbO12 cuboctahedra, faces with four equivalent ReO6 octahedra, and faces with four equivalent CoO6 octahedra. All Pb–O bond lengths are 2.85 Å. O2- is bonded in a distorted linear geometry to one Re6+, one Co2+, and four equivalent Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr2InOsO6 by Materials Project

Sr2OsInO6 is (Cubic) Perovskite-derived structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Sr2+ is bonded to twelve equivalent O2- atoms to form SrO12 cuboctahedra that share corners with twelve equivalent SrO12 cuboctahedra, faces with six equivalent SrO12 cuboctahedra, faces with four equivalent OsO6 octahedra, and faces with four equivalent InO6 octahedra. All Sr–O bond lengths are 2.90 Å. Os5+ is bonded to six equivalent O2- atoms to form OsO6 octahedra that share corners with six equivalent InO6 octahedra and faces with eight equivalent SrO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All Os–O bond lengths are 1.97 Å. In3+ is bonded to six equivalent O2- atoms to form InO6 octahedra that share corners with six equivalent OsO6 octahedra and faces with eight equivalent SrO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All In–O bond lengths are 2.13 Å. O2- is bonded in a distorted linear geometry to four equivalent Sr2+, one Os5+, and one In3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K2HgSbBr6 by Materials Project

K2HgSbBr6 is (Cubic) Perovskite-derived structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. K1+ is bonded to twelve equivalent Br1- atoms to form KBr12 cuboctahedra that share corners with twelve equivalent KBr12 cuboctahedra, faces with six equivalent KBr12 cuboctahedra, faces with four equivalent HgBr6 octahedra, and faces with four equivalent SbBr6 octahedra. All K–Br bond lengths are 4.08 Å. Hg1+ is bonded to six equivalent Br1- atoms to form HgBr6 octahedra that share corners with six equivalent SbBr6 octahedra and faces with eight equivalent KBr12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All Hg–Br bond lengths are 2.96 Å. Sb3+ is bonded to six equivalent Br1- atoms to form SbBr6 octahedra that share corners with six equivalent HgBr6 octahedra and faces with eight equivalent KBr12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All Sb–Br bond lengths are 2.81 Å. Br1- is bonded in a linear geometry to four equivalent K1+, one Hg1+, and one Sb3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs2InAsI6 by Materials Project

Cs2InAsI6 is (Cubic) Perovskite-derived structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Cs1+ is bonded to twelve equivalent I1- atoms to form CsI12 cuboctahedra that share corners with twelve equivalent CsI12 cuboctahedra, faces with six equivalent CsI12 cuboctahedra, faces with four equivalent InI6 octahedra, and faces with four equivalent AsI6 octahedra. All Cs–I bond lengths are 4.33 Å. In1+ is bonded to six equivalent I1- atoms to form InI6 octahedra that share corners with six equivalent AsI6 octahedra and faces with eight equivalent CsI12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All In–I bond lengths are 3.21 Å. As3+ is bonded to six equivalent I1- atoms to form AsI6 octahedra that share corners with six equivalent InI6 octahedra and faces with eight equivalent CsI12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All As–I bond lengths are 2.91 Å. I1- is bonded to four equivalent Cs1+, one In1+, and one As3+ atom to form a mixture of distorted edge, face, and corner-sharing ICs4InAs octahedra. The corner-sharing octahedra tilt angles range from 0–60°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SrCaTiMnO6 by Materials Project

SrCaTiMnO6 is (Cubic) Perovskite-derived structured and crystallizes in the tetragonal P4mm space group. The structure is three-dimensional. Sr2+ is bonded to twelve O2- atoms to form SrO12 cuboctahedra that share corners with four equivalent SrO12 cuboctahedra, corners with eight equivalent CaO12 cuboctahedra, faces with two equivalent CaO12 cuboctahedra, faces with four equivalent SrO12 cuboctahedra, faces with four equivalent TiO6 octahedra, and faces with four equivalent MnO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.75–2.78 Å. Ca2+ is bonded to twelve O2- atoms to form CaO12 cuboctahedra that share corners with four equivalent CaO12 cuboctahedra, corners with eight equivalent SrO12 cuboctahedra, faces with two equivalent SrO12 cuboctahedra, faces with four equivalent CaO12 cuboctahedra, faces with four equivalent TiO6 octahedra, and faces with four equivalent MnO6 octahedra. There are a spread of Ca–O bond distances ranging from 2.63–2.78 Å. Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with two equivalent MnO6 octahedra, corners with four equivalent TiO6 octahedra, faces with four equivalent SrO12 cuboctahedra, and faces with four equivalent CaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–2°. There are a spread of Ti–O bond distances ranging from 1.89–2.03 Å. Mn4+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with two equivalent TiO6 octahedra, corners with four equivalent MnO6 octahedra, faces with four equivalent SrO12 cuboctahedra, and faces with four equivalent CaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–5°. There are a spread of Mn–O bond distances ranging from 1.89–1.94 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted linear geometry to four equivalent Sr2+, one Ti4+, and one Mn4+ atom. In the second O2- site, O2- is bonded in a distorted linear geometry to four equivalent Ca2+, one Ti4+, and one Mn4+ atom. In the third O2- site, O2- is bonded in a distorted linear geometry to two equivalent Sr2+, two equivalent Ca2+, and two equivalent Ti4+ atoms. In the fourth O2- site, O2- is bonded in a distorted linear geometry to two equivalent Sr2+, two equivalent Ca2+, and two equivalent Mn4+ atoms.

36 MATERIALS SCIENCE↗