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A novel high-voltage solid solution of Li2CoxMn1–x(SO4)2 (x = 0–1) was synthesized using a simple solid-state reaction. Single-phase monoclinic crystal structure was identified, and there was no evidence for the presence of an orthorhombic polymorph at a sample preparation temperature of 450 °C. Interestingly, the bimetallic sulfates were found to be thermally stable up to 550 °C, and it was validated through various characterization techniques. Beyond 550 °C, the materials start to decompose and form Li2SO4 and α-CoSO4 in the case of Li2Co(SO4)2, while Li2Mn(SO4)2 decomposes to form Li2Mn2(SO4)3. In addition, an important property called sensitivity toward moisture was also characterized, which plays a critical role in the handling of the sulfate-based cathode during the cell fabrication. Thus, the reaction mechanism involved during the absorption of the atmospheric moisture was also investigated carefully. Finally, for the first time electrochemical activity of both Co and Mn systems was discovered wher...

To control the process of cation exchange (CE) in a multielemental system, a detailed understanding of structural changes at the microscopic level is imperative. However, the synthesis of a multielemental system has so far relied on the CE phenomenon of a binary system, which does not necessarily extend to the higher-order systems. Here, direct experimental evidence supported by theoretical calculations reveals a growth model of binary Cu–S to ternary Cu–Sn–S to quaternary Cu–Zn–Sn–S, which shows that cations preferentially diffuse along a specific lattice plane with the preservation of sulfuric anionic framework. In addition, we also discover that, unlike the commonly accepted structure (P63mc), the metastable crystal structure of Cu–Zn–Sn–S phase possesses fixed Sn occupancy sites. By revealing the preferential nature of cations diffusion and growth mechanism, our work provides insight into controlling the stoichiometry and phase purity of novel multielemental materials. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version We acknowledge financial support from National Research Foundation (NRF), Singapore, through the Singapore-Berkeley Research Initiative for Sustainable Energy (SinBeRISE) and Nanomaterials for Energy and Water Management (SHARE NEW) CREATE program. L.H.W. thanks the funding support from Singapore Ministry of Education, Tier 2 (2016-T2-1-030). S.L. acknowledges the funding support from Singapore Ministry of Education Tier 1 (107/15). H.Z. thanks the funding support from U.S. DOE BES Materials Sciences and Engineering Division Under Contract No. KC22ZH. X.Y.L. thanks the funding support from Singapore Ministry of Education, Tier 1 (RG21/16) and Tier 2 (MOE2016-T2-1- 043) grants.. The work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. We thank Fiona Doyle for lending us her synthetic laboratory in University of California Berkeley (UCB), Song Chengyu and Karen Bustilo for their help and assistance on TEM, and Matthew P. Sherburne for nanoparticle growth discussion.

The 1H and 13C NMR spectra in methylammonium lead halide perovskites, CH3NH3PbX3 (X = I, Br and Cl) show that the CH3NH3+ units undergo dynamic reorientation, as the organic component tumbles in the perovskite cage. In addition, the differences in the anomalously long relaxation times of the protons associated with the CH3 and not the NH3 groups indicate that only the amine end of the CH3NH3+ group is interacting with the inorganic network. Using this information, we have refined some single crystal X-ray and neutron diffraction data to probe their unusual structures in more detail. Furthermore, impedance spectroscopy has been used to monitor the high-temperature phase transition of CH3NH3PbI3, which confirms a significant increase in conductivity, when it is in its high temperature and higher symmetry structural regime. The optical band-gaps of each halide perovskite were determined using UV-visible spectroscopy and are consistent with previous reports. NRF (Natl Research Foundation, S’pore) Accepted version

Lead-containing (Pb-B-X)-2Hapatites encompass a number of [AF]4[AT]6[(BO4)6]X2compounds used for waste stabilization, environmental catalysis and ion conduction, but the influence of the stereochemically active lone-pair electrons of Pb2+on crystal chemistry and functionality is poorly understood. This article presents a compilation of existing structural data for Pb apatites that demonstrate paired electrons of Pb2+at both theAFandATresults in substantial adjustments to the PbFO6metaprism twist angle, φ. New structure refinements are presented for several natural varieties as a function of temperature by single-crystal X-ray diffraction (XRD) of vanadinite-2H(ideally Pb10(VO4)6Cl2), pyromorphite-2H(Pb10(PO4)6Cl2), mimetite-2H/M(Pb10(As5+O4)6Cl2) and finnemanite-2H(Pb10(As3+O3)6Cl2). A supercell for mimetite is confirmed using synchrotron single-crystal XRD. It is suggested the superstructure is necessary to accommodate displacement of the stereochemically active 6s2lone-pair electrons on the Pb2+that occupy a volume similar to an O2−anion. We propose that depending on the temperature and concentration of minor substitutional ions, the mimetite superstructure is a structural adaptation common to all Pb-containing apatites and by extension apatite electrolytes, where oxide ion interstitials are found at similar positions to the lonepair electrons. It is also shown that plumbous apatite framework flexes substantially through adjustments of the PbFO6metaprism twist-angles (φ) as the temperature changes. Finally, crystalchemical [100] zoning observed at submicron scales will probably impact on the treatment of diffraction data and may account for certain inconsistencies in reported structures.

The paradigm that functional materials are adequately described as three-dimensional crystal structures is not universally tenable. Gallate melilites are efficient oxide ion conductors at intermediate temperatures (∼750 °C) with non-rational crystallographic modulations presumed to play a key role in significantly enhancing oxygen mobility. Lattice distortions associated with incommensuration are usually extrapolated from diffraction analysis of volumes greatly exceeding the scale of modulation. Therefore, opportunities for making direct nanometric measurements are exceptionally valuable for correlating structure with function. In [Ca Ln ] 2 [Ga] 2 [Ga 2 O 7 ] 2 ( Ln =Nd, La) melilites, atomic displacive and compositional modulation waves can be imaged by high angle annular dark field and bright field scanning transmission electron microscopy with contrast quantified through electron scattering simulation. Here, we present atomic scale observations of (3+2)-dimensional modulations in gallate melilites which expands our understanding of the ion conduction mechanism and provides guidance for enhancing the performance of solid oxide fuel cells through crystal chemical tailoring.

We report the pressure-induced crystallographic transitions and optical behavior of MAPbI3 (MA=methylammonium) using in situ synchrotron X-ray diffraction and laser-excited photoluminescence spectroscopy, supported by density functional theory (DFT) calculations using the hybrid functional B3PW91 with spin-orbit coupling. The tetragonal polymorph determined at ambient pressure transforms to a ReO3-type cubic phase at 0.3 GPa. Upon continuous compression to 2.7 GPa this cubic polymorph converts into a putative orthorhombic structure. Beyond 4.7 GPa it separates into crystalline and amorphous fractions. During decompression, this phase-mixed material undergoes distinct restoration pathways depending on the peak pressure. In situ pressure photoluminescence investigation suggests a reduction in band gap with increasing pressure up to ≈0.3 GPa and then an increase in band gap up to a pressure of 2.7 GPa, in excellent agreement with our DFT calculation prediction. This work lays the foundation for understanding the pressure-dependent phase transition of MAPbI3 and potentially enriches the toolkit for engineering perovskite polymorphs with exceptional optical properties. NRF (Natl Research Foundation, S’pore) Accepted version

A gem-grade apatite from Brazil of general composition (Ca,Na) 10 [(P,Si,S)O 4 ] 6 (F,Cl,OH) 2 has been studied using single-crystal X-ray and neutron diffraction together with synchrotron powder X-ray diffraction. Earlier electron microscopy studies had shown the nominally single-phase apatite contains an abundant fluorapatite (F - Ap) host, together with chloro-hydroxylapatites (Cl/OH - Ap) guest phases that encapsulate hydroxylellestadite (OH - El) nanocrystals. While the latter features appear as small (200–400 nm) chemically distinct regions by transmission electron microscopy, and can be identified as separate phases by synchrotron powder X-ray diffraction, these could not be detected by single-crystal X-ray and neutron analysis. The observations using neutron, X-ray and electron probes are however consistent and complementary. After refinement in the space group P 6 3 / m the tunnel anions F − are fixed at z = ¼ along , while the anions Cl − and OH − are disordered, with the suggestion that O-H···O-H··· hydrogen-bonded chains form in localized regions, such that no net poling results. The major cations are located in the 4 f A F O 6 metaprism (Ca+Na), 6 h A T O 6 X tunnel site (Ca only), and 6 h B O 4 tetrahedron (P+Si+S). The structural intricacy of this gem stone provides further evidence that apatite microstructures display a nano-phase separation that is generally unrecognized, with the implication that such complexity may impact upon the functionality of technological analogues.

[ A I ] 4 [ A II ] 6 ( B O 4 ) 6 X 2 apatites can flexibly accommodate numerous cationic, metalloid and anionic substitutions. Using a combination of new refinements and published structures, this paper reviews correlations between substituent type and framework adaptation through adjustment of the A I O 6 metaprism twist angle, φ . These systematics are illustrated through powder neutron diffraction refinement of the crystal chemistry of A 10 (PO 4 ) 6 F 2 ( A =Ca, Sr) fluorapatites. Variations in φ reflect changes in the relative size of the A I 4 ( B O 4 ) 6 framework and A II 6 X 2 tunnel content and can be used to quantitatively assess the reliability of A I / A II cation partitioning coefficients determined by Rietveld analysis. In the simplest cases of bi-ionic substitution, the metaprism twist systematics conform to three principle trends (i) For A -type divalent substitution, the larger A 2 + species preferentially enters the channel before partitioning to the framework. This leads to parabolic modification in φ across the compositional series; (ii) For B -type pentavalent compounds, the φ variation will be linear in accord with the relative B 5+ ionic size; and (iii) For X -type substitution of halide anions, φ will be reduced as the average size increases. Departures from these trends may indicate polymorphism, compositional anomalies, A I /A II order disequilibrium, or poor structure refinement, and may be extended to chemically complex apatites with simultaneous substitutions over the A , B and X sites.

Lanthanoid silicates (Ln9.33Si6O26) adopt the hexagonal apatite structure and show potential as solid oxide fuel cell (SOFC) electrolytes due to their high oxide ion conductivity at intermediate temperatures (500–700 °C). Ions migrate preferentially along the crystallographic c-axis, and can be improved by introducing lower valent elements at the silicon sites. To better understand this phenomenon, single crystals of aluminium-doped neodymium silicate Nd9.33+x/3AlxSi6−xO26 (0≤x≤1) were synthesised using the floating-zone method in an inert environment at a growth rate of 5 mm/L. The products with x

The crystal chemistries of synthetic mimetite, Pb10(As5+O4)6(Cl2 − x O x/2), a neutral apatite, and finnemanite, Pb10(As3+O3)6Cl2, a reduced apatite, were characterized using a combination of X-ray powder diffraction, neutron diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Both phases conform to hexagonal P63/m symmetry; however, the temperature-driven transformation of clinomimetite to mimetite described earlier was not confirmed. The average mimetite structure is best described through the introduction of partially occupied oxygen sites. A better understanding of the mixed arsenic speciation in apatites can guide the formulation of waste form ceramics and improve models of long-term durability after landfill disposal.

Extraction of reliable bond distances and angles for Ca10(V x P1 − x O4)6F2 apatites using standard Rietveld refinement with Cu Kα X-ray powder data was significantly impaired by large imprecision for the O-atom coordinates. An initial attempt to apply crystal-chemical Rietveld refinements to the same compounds was partly successful, and exposed the problematic determination of two oxygen–metal–oxygen angles. Ab initio modeling with VASP in space groups P63/m, P21/m and Pm showed that both these angular parameters exhibited a linear dependence with the vanadium content. Stable crystal-chemical Rietveld refinements in agreement with quantum results were obtained by fixing these angles at the values from ab initio simulations. Residuals were comparable with the less precise standard refinements. The larger vanadium ion is accommodated primarily by uniform expansion and rotation of BO4 tetrahedra combined with a rotation of the Ca–Ca–Ca triangular units. It is proposed that the reduction of symmetry for the vanadium end-member is necessary to avoid considerable departures from formal valences at the A II and B sites in P63/m. The complementarity of quantum methods and structural analysis by powder diffraction in cases with problematic least-squares extraction of the crystal chemistry is discussed.

Lanthanoid silicate apatite solid electrolytes contain one-dimensional channels. These materials display substantial oxygen mobility at temperatures lower than conventional zirconia-based ionic conductors because interstitial oxygen displacements, mediated by Ln cation vacancies, have a lower activation energy. For these nonstoichiometric apatites, crystal structure solutions derived from X-ray and neutron powder diffraction yield the average atomic arrangement, but these techniques also average over local lattice disorders. Large apatite single crystals permit the evaluation of oxygen migration anisotropy using impedance spectroscopy and the correlation of this behavior to atomic scale domain formation or defect cluster aggregation if present. Aberration-corrected scanning transmission electron microscopy, in both high angle annular dark field (HAADF) and bright field (BF) modalities, was applied to characterize the local atomic structure of Nd9.33Si6O26 and Nd8Sr2Si6O26 apatite electrolytes. Quantitative image analysis found the distribution of metal vacancies and dopant metal in apatites to be remarkably homogeneous at the unit cell scale. This is distinct from other oxide electrolytes including fluorites, perovskites, and melilites, where domain and superstructure formation are a consequence of interstitial oxygen incorporation and prescribe the mode of ionic transport. In the present case, the unexpectedly high perfection of silicate apatites arises from the flexible topological response of one-dimensional channels penetrating the structure, which, in turn, allows robust chemical tailoring of these electrolytes. ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Accepted version

et al., A single-crystal structure determination of Nd8Sr 2Si6O26 apatite, a prototype intermediate-temperature electrolyte for solid oxide fuel cells grown by the floating-zone method, was completed using the combination of Laue neutron diffraction and Raman spectroscopy. While neutron diffraction was in good agreement with P63/m symmetry, the possibility of P63 could not be convincingly excluded. This ambiguity was removed by the collection of orientation-dependent Raman spectra that could only be consistent with P63/m. The composition of Nd8Sr2Si 6O26 was independently verified by powder X-ray diffraction in combination with electron probe microanalysis, with the latter confirming a homogeneous distribution of Sr and the absence of chemical zonation commonly observed in apatites. This comprehensive crystallochemical description of Nd8Sr2Si6O26 provides a baseline to quantify the efficacy of cation vacancies, oxygen superstoichiometry, and symmetry modification for promoting oxygen-ion mobility. © 2014 American Chemical Society., This work was supported by A*STAR (Agency for Science, Technology and Research) SERC Grant 082 101 0021 (“Optimization of Apatite Anion Sublattices in Solid Oxide Fuel Cell Electrolytes”) and by Spanish Government Grant MAT2010-19837-C06-06. A.O. acknowledges financial support provided by the Spanish Ministerio de Ciencia e Innovación through a Juan de la Cierva contract.

Large fergusonite-type (ABO4, A=Ce, B=Nb) oxide crystals, a prototype electrolyte composition for solid oxide fuel cells (SOFC), were prepared for the first time in a floating zone mirror furnace under air or argon atmospheres. While CeNbO4 grown in air contained CeNbO4.08 as a minor impurity that compromised structural analysis, the argon atmosphere yielded a single phase crystal of monoclinic CeNbO4, as confirmed by selected area electron diffraction, powder and single crystal X-ray diffraction. The structure was determined in the standard space group setting C12/c1 (No. 15), rather than the commonly adopted I12/a1. AC impedance spectroscopy conducted under argon found that stoichiometric CeNbO4 single crystals showed lower conductivity compared to CeNbO4+δ confirming interstitial oxygen can penetrate through fergusonite and is responsible for the higher conductivity associated with these oxides. Accepted version

Melilite-type [A(2)](2)[B(I)](2)[B(II)(2)O(7)](2) gallates are promising ion conducting electrolytes for deployment in solid oxide fuel cells. Single crystals of [CaLa](2)[Ga](2)[Ga(2)O(7)](2), grown in an optical floating zone furnace, were investigated using a combination of transmission electron microscopy and single crystal X-ray diffraction. Strong anisotropic displacements of oxygen arise from the structural misfit between the interlayer Ca/La cations and the [Ga]-[Ga(2)O(7)] tetrahedral layers. A model employing two-dimensional modulation achieves bond lengths and bond angles that preserve satisfactory bond valence sums throughout the structure. The melilite belongs to the tetragonal superspace group P42(1)m(α, α, 0)00s(α, α, 0)000, α = 0.2160(5), with a subcell metric of a = 7.9383(2) A, c = 5.2641(3) A, onto which modulation vectors are superimposed: q(1) = α (a* + b*), q(2) = α (-a* + b*). Both displacive (cation and anion) and occupational (cation) modulations contribute to incommensuration. The analysis of structural adjustments that accompany changes in temperature and composition provides assurance that the crystal chemical model is correct. By better understanding the flexibility of this modulated structure a rational approach toward crystallochemical optimization of electrolyte performance by enhancing oxygen mobility becomes feasible.

Melilite-type gallium oxides are potential intermediate temperature electrolytes for solid oxide fuel cells. Single crystals of [CaNd]2[Ga]2[Ga2O7]2 grown using an optical floating zone furnace have been investigated using transmission electron microscopy and powder and single-crystal X-ray diffraction. The anion array topologically conforms to a [(3.5.4.5)2, 3.5.3.5] network that contains distorted pentagonal tunnels. The distortion is necessary to achieve space filling and accommodate structural misfit between the layers. Satisfactory bond lengths and angles are obtained through two-dimensional modulation in the tetragonal based plane, leading to five-dimensional symmetry in the superspace group P4̅21m(α,α,0)00s(α̅a̅,a,0)000, α = 0.2319(2), with modulation vectors q1 = α(a* + b*) and q2 = α(−a* + b*). Both displacive and occupational modulations are found. Through this mechanism, melilites are primed to accommodate mobile oxygen interstitials, suggesting a rational approach to crystallochemical tailoring that will enhance ionic diffusion and optimize electrolyte performance. MOE (Min. of Education, S’pore) Accepted version

et al., High oxygen content apatite germanates, La10Ge 6-xWxO27+x, have been prepared by doping on the Ge site with W. In addition to increasing the oxygen content, this doping strategy is shown to result in stabilisation of the hexagonal lattice, and yield high conductivities. Structural studies of La10Ge 5.5W0.5O27.5 show that the interstitial oxygen sites are associated to a different degree with the Ge/WO4 tetrahedra, leading to five coordinate Ge/W and significant disorder for the oxygen sites associated with these units. Raman spectroscopy studies suggest that in the case of the WO5 units, the interstitial oxygen is more tightly bonded and therefore not as mobile as in the case of the GeO5 units, thus not contributing significantly to the conduction process. © 2011 The Royal Society of Chemistry., Financial support from Spanish project MAT2007-64486-C07-02 is acknowledged.

Solid-state reaction between SrCO{sub 3}, Cr{sub 2}O{sub 3} and SrF{sub 2} has produced the apatite phase Sr{sub 10}(CrO{sub 4}){sub 6}F{sub 2} and Sr{sub 2}CrO{sub 4} which adopts the K{sub 2}NiF{sub 4}-type structure. The reaction outcome was very sensitive to the heating rate with rapid rise times favouring the formation of Sr{sub 2}CrO{sub 4}, which has been synthesised at ambient pressure for the first time. Powder X-ray diffraction and electron diffraction confirmed that Sr{sub 2}CrO{sub 4} adopts a body centred tetragonal cell (space group I4/mmm) with lattice parameters a=3.8357(1) A and c=12.7169(1) A, while a combination of neutron and X-ray diffraction verified Sr{sub 10}(CrO{sub 4}){sub 6}F{sub 2} is hexagonal (space group P6{sub 3}/m) with lattice parameters a=9.9570(1) A and c=7.4292(1) A. X-ray photoelectron spectroscopy and magnetic measurements were used to characterise the oxidation states of chromium contained within these phases. - Graphical abstract: A solid-state reaction between SrCO{sub 3}, Cr{sub 2}O{sub 3} and SrF{sub 2} produced Sr{sub 10}(CrO{sub 4}){sub 6}F{sub 2} apatite and Sr{sub 2}CrO{sub 4} which adopts the K{sub 2}NiF{sub 4}-type structure. Powder X-ray and electron diffraction confirmed that Sr{sub 2}CrO{sub 4} is body-centred tetragonal, while a combination of neutron and X-ray diffraction verified Sr{sub 10}(CrO{sub 4}){sub 6}F{sub 2} ismore » hexagonal. X-ray photoelectron spectroscopy and magnetic measurements identified the oxidation states of chromium in these phases.« less

Solid-state reaction between SrCO{sub 3}, Cr{sub 2}O{sub 3} and SrF{sub 2} has produced the apatite phase Sr{sub 10}(CrO{sub 4}){sub 6}F{sub 2} and Sr{sub 2}CrO{sub 4} which adopts the K{sub 2}NiF{sub 4}-type structure. The reaction outcome was very sensitive to the heating rate with rapid rise times favouring the formation of Sr{sub 2}CrO{sub 4}, which has been synthesised at ambient pressure for the first time. Powder X-ray diffraction and electron diffraction confirmed that Sr{sub 2}CrO{sub 4} adopts a body centred tetragonal cell (space group I4/mmm) with lattice parameters a=3.8357(1) A and c=12.7169(1) A, while a combination of neutron and X-ray diffraction verified Sr{sub 10}(CrO{sub 4}){sub 6}F{sub 2} is hexagonal (space group P6{sub 3}/m) with lattice parameters a=9.9570(1) A and c=7.4292(1) A. X-ray photoelectron spectroscopy and magnetic measurements were used to characterise the oxidation states of chromium contained within these phases. - Graphical abstract: A solid-state reaction between SrCO{sub 3}, Cr{sub 2}O{sub 3} and SrF{sub 2} produced Sr{sub 10}(CrO{sub 4}){sub 6}F{sub 2} apatite and Sr{sub 2}CrO{sub 4} which adopts the K{sub 2}NiF{sub 4}-type structure. Powder X-ray and electron diffraction confirmed that Sr{sub 2}CrO{sub 4} is body-centred tetragonal, while a combination of neutron and X-ray diffraction verified Sr{sub 10}(CrO{sub 4}){sub 6}F{sub 2} ismore » hexagonal. X-ray photoelectron spectroscopy and magnetic measurements identified the oxidation states of chromium in these phases.« less

Ba(2)CoS(3) is the first example of an inorganic solid containing one-dimensional corner-sharing [Co(2+)-anion] chains, which leads to one-dimensional cooperative antiferromagnetism.

The first series of alkaline-earth palladium oxide–fluorides Ba2−xSrxPdO2F2 (0 ≤ x ≤ 1.5) display the T′ structure (Nd2CuO4) instead of the predicted T structure (La2CuO4), showing that electronic factors prevail over steric factors.

Apatite-like materials are of considerable interest as potential solid oxide fuel cell electrolytes, although their structural vagaries continue to attract significant discussion. Understanding these features is crucial both to explain the oxide ion conduction process and to optimise it. As the composition of putative P6(3)/m apatites with ideal formula [A(I)(4)][A(II)(6)][(BO(4))(6)][X](2) is varied the [A(I)(4)(BO(4))(6)] framework will flex to better accommodate the [A(II)(6)X(2)] tunnel component through adjustment of the A(I)O(6) metaprism twist angle (varphi). The space group theory prescribes that framework adaptation during phase changes must lead to one of the maximal non-isomorphic subgroups of P6(3)/m (P2(1), P2(1)/m, P1[combining macron]). These adaptations correlate with oxygen ion conduction, and become crucial especially when the tunnels are filled by relatively small ions and/or partially occupied, and if interstitial oxygens are located in the framework. Detecting and completely describing these lower symmetry structures can be challenging, as it is difficult to precisely control apatite stoichiometry and small departures from the hexagonal metric may be near the limits of detection. Using a combination of diffraction and spectroscopic techniques it is shown that lanthanum strontium germanate oxide electrolytes crystallise as triclinic (A), monoclinic (M) and hexagonal (H) bi-layer pseudomorphs with the composition ranges: [La(10-x)Sr(x)][(GeO(4))(5+x/2)(GeO(5))(1-x/2)][O(2)] (0or=xor= 1) apatite-2A[La(10-x)Sr(x)][(GeO(4))(5+x/2)(GeO(5))(1-x/2)][O(2)] (1or=xor= 2) apatite-2M[La(10-x)Sr(x)][(GeO(4))(6)][O(2)][H(delta)] (2or=xor= 2.96) apatite-2M[La(10-x)Sr(x)][(GeO(4))(6)][O(2)][H(delta)] (2.96or=xor= 5.32) apatite-2HFurthermore, at typical fuel cell operating temperatures apatite-2A and apatite-2M will transform to apatite-2H, with the latter showing the highest conduction. The results show that small twist angles and high symmetry enhance oxygen mobility with these properties tailored by adjusting the relative size of the framework to tunnel. This information can hence aid in the design of new materials with improved oxide ion conductivity.

The crystal chemistry of the cuprate apatites A(I)(4)A(II)(6)(PO(4))(6)Cu(x)O(y)(H)(z) (A = Ca, Sr and Ba) was investigated by powder X-ray (PXRD) and neutron diffraction (PND) and X-ray photoelectron spectroscopy (XPS). The refined crystal structures confirmed earlier X-ray diffraction studies that showed copper resides in the apatite channels and additionally, located hydrogen. For all materials copper is primarily divalent (Cu(2+)) but in the calcium and strontium analogues co-exists with minor Cu(3+). This is in contrast with a previous work where Cu(1+) and Cu(2+) were reported.

Ba2CoS3 is the first example of an inorganic solid containing one-dimensional corner-sharing [Co2+–anion] chains, which leads to one-dimensional cooperative antiferromagnetism.

The pressure-induced structural evolution of formamidinium-based perovskite FAPbI3 was investigated using in situ synchrotron X-ray diffraction and laser-excited photoluminescence methods. Cubic α-FAPbI3 ( Pm3̅ m) partially and irreversibly transformed to hexagonal δ-FAPbI3 ( P63 mc) at a pressure less than 0.1 GPa. Structural transitions of α-FAPbI3 followed the sequence of Pm3̅ m → P4/ mbm → Im3̅ → partial amorphous during compression to 6.59 GPa, whereas the δ-phase converted to an orthorhombic Cmc21 structure between 1.26 and 1.73 GPa. During decompression, FAPbI3 recovered the P63 mc structure of the δ-phase as a minor component (∼18 wt %) from 2.41-1.40 GPa and the Pm3̅ m structure of the α-phase becomes dominant (∼82 wt %) at 0.10 GPa but with an increased fraction of δ-FAPbI3. The photoluminescence behaviors from both the α- and δ-forms were likely controlled by radiative recombination at the defect levels rather than band-edge emission during pressure cycling. FAPbI3 polymorphism is exquisitely sensitive to pressure. While modest pressures can engineer FAPbI3-based photovoltaic devices, irreversible δ-phase crystallization may be a limiting factor and should be taken into account.