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Lithium-oxide-halide and lithium-hydroxide-halide antiperovskites were explored for potential electrolytes in all-solid Li-ion batteries. A single-phase sample of the Ruddlesden–Popper (RP) series of compounds, LiBr(Li2OHBr)2 with double antiperovskite Li2OHBr layers and rigid rock-salt type LiBr layers, was obtained. Li+-ion vacancies are introduced in the double antiperovskite Li2OHBr layers but not in the LiBr layers and induce two-dimensional Li-ion conduction with low activation energy by mediating Li-ion hopping. In contrast to the Br-containing RP phase, Cl-containing Li-oxide-halide and Li-hydroxide-halide RP phases cannot be crystallized due to the structural mismatch between the antiperovskite layers and rigid LiCl layers.

We have successfully grown single crystals of $\mathrm{Pb}{\mathrm{Mn}}_{2}{\mathrm{Ni}}_{6}{\mathrm{Te}}_{3}{\mathrm{O}}_{18}$ and present a comprehensive study of their magnetic, thermodynamic, and Raman spectroscopic properties. $\mathrm{Pb}{\mathrm{Mn}}_{2}{\mathrm{Ni}}_{6}{\mathrm{Te}}_{3}{\mathrm{O}}_{18}$ consists of a planar network of pairwise rotated $\mathrm{Ni}{\mathrm{O}}_{6}$ dimers coupled by corners. Similarities to ${\mathrm{Ni}}_{3}\mathrm{Te}{\mathrm{O}}_{6}$ exist, which forms honeycomb layers. The magnetic susceptibility \ensuremath{\chi} and heat capacity ${C}_{p}$ data reveal an antiferromagnetic phase transition around 84 K, which is evidently hysteretic on warming and cooling between 94 and 40 K with a loop width of about 1.83\ifmmode\pm\else\textpm\fi{} 0.41 K; thus the transition appears to be of first order. \ensuremath{\chi} is anisotropic, with larger values for in-plane fields over the entire measured temperature range. Raman spectroscopy has been employed to investigate the lattice and magnetic excitations of the $\mathrm{Pb}{\mathrm{Mn}}_{2}{\mathrm{Ni}}_{6}{\mathrm{Te}}_{3}{\mathrm{O}}_{18}$ from 5 to 300 K. Besides an anharmonic phonon behavior, i.e., a decay into acoustic phonons, we find a coupling to the spin system at ${T}_{N}=84\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, as well as weak anomalies at ${T}^{*}\ensuremath{\approx}200\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. This second characteristic temperature gives evidence for an instability of the coupled spin/lattice system, as here the phonon linewidths and intensities evidence similar behavior as at ${T}_{N}=84\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Furthermore, magnetic Raman scattering at $240\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$ is used to estimate an exchange coupling of $J=--86\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ in general agreement with the Curie-Weiss temperature.

A fully oxygenated hexagonal 12-layer perovskite $\mathrm{BaFe}{\mathrm{O}}_{3}$ with nominal $\mathrm{F}{\mathrm{e}}^{4+}$ was obtained by high-pressure synthesis. The structure consists of face-sharing $\mathrm{F}{\mathrm{e}}_{3}{\mathrm{O}}_{9}$ octahedral trimers and corner-sharing octahedra. A remarkable series of electronic transitions that relieve the electronic instability of $\mathrm{F}{\mathrm{e}}^{4+}$ are discovered on cooling; $2\mathrm{F}{\mathrm{e}}^{4+}\ensuremath{\rightarrow}\mathrm{F}{\mathrm{e}}^{3+}+\mathrm{F}{\mathrm{e}}^{5+}$ charge disproportionation and ordering over two sites accompanied by a structural distortion at 500 K; charge disproportionation of the remaining $\mathrm{F}{\mathrm{e}}^{4+}$ with magnetic order at 280 K; and an unprecedented charge interchange where $\mathrm{F}{\mathrm{e}}^{3+}$ and $\mathrm{F}{\mathrm{e}}^{5+}$ states are exchanged between two sites with spin orientation change at 50 K. These properties demonstrate the presence of multiple competing ground states in this complex, highly condensed network of corner- and face-sharing octahedra.

Recently, Ag–Bi–I system has attracted significant attention as an emergent material for absorbers in solar cells. We have investigated the single-phase compositions, analyzed the detailed crystal structures, measured optical and electronic properties, and determined the structure–property relations of Ag2−3xBixI2. Single-phase samples with CdCl2-type rhombohedral structures were obtained with Ag-rich compositions (x = 0.45–0.48), while defect-spinel-type cubic structures were stabilized with Bi-rich compositions (x = 0.52–0.57). Both the rhombohedral and cubic structures consisted of the cubic close-packed I-ion sublattices, and the small difference in the Ag/Bi composition resulted in distinct crystal structures. Both the CdCl2-type rhombohedral and defect-spinel-type cubic compounds exhibited semiconducting behavior with proper band gap energies, which indicates that both materials are potentially useful as absorbers in solar cells. The rhombohedral structure compounds have shallower valence band energies, larger indirect band gap energies, and higher electrical conductivity with lower activation energy than the cubic structure compounds. The distinct properties result from the difference in the defect structures, additional Ag occupation in the rhombohedral phase and deficiencies of the octahedral site in the cubic phase.

BaFexNi1–xO3 with end members of BaNiO3 (x = 0) and BaFeO3 (x = 1), which, respectively, adopt the 2H and 6H hexagonal perovskite structures, were synthesized, and their crystal structures were investigated. A new single phase, Ba4Fe3NiO12 (x = 0.75), that adopts the 12R perovskite structure with the space group R3m (a = 5.66564(7) A and c = 27.8416(3) A), was found to be stabilized. Mossbauer spectroscopy results and structure analysis using synchrotron and neutron powder diffraction data revealed that nominal Fe3+ occupies the corner-sharing octahedral site while the unusually high valence Fe4+ and Ni4+ occupy the face-sharing octahedral sites in the trimers, giving a charge formula of Ba4Fe3+Fe4+2Ni4+O11.5. The magnetic properties of the compound are also discussed.

A Sr analogue of Ca0.5Bi0.5FeO3, Sr0.5Bi0.5FeO3, containing unusually high valence Fe3.5+ ions was synthesized by using a high-pressure technique. It relieves the electronic instability due to the unusually high valence of Fe3.5+ by a single charge disproportionation (CD) transition (Fe3.5+ -> 0.75Fe(3+) + 0.25Fe(5+)) rather than the successive CD and intermetallic charge transfer (CT) transitions seen in Ca0.5Bi0.5FeO3. Conduction-band narrowing due to the significant bend in the Fe-O-Fe bond in the rhombohedral R (3) over barc crystal structure stabilized the charge-disproportionated state at low temperatures. Most importantly, Bi3+ ions in Sr0.5Bi0.5FeO3 do not act as countercations accepting oxygen holes as they do in Ca0.5Bi0.5FeO3, resulting in the absence of the intermetallic CT transition. The large cavity of the A-site Sr ions prevents the charge-transferred Bi5+ from being stabilized. In the charge-disproportionated state the nearest-neighbor Fe3+ spins align antiferromagnetically and one-fourth of the Fe3+ spins are randomly replaced by Fe5+ spins coupled ferromagnetically with the neighboring Fe3+ spins.

We investigated moderate-temperature oxygen diffusion mechanisms in Sr2ScGaO5 with Brownmillerite structure type. From oxygen isotope 18O−16O exchange experiments we determined that oxygen mobility sets in above 550 °C. Temperature-dependent neutron and X-ray (synchrotron) diffraction experiments allowed us to correlate the oxygen mobility with a subtle phase transition of the orthorhombic room-temperature structure with I2mb space group toward Imma, going along with a disorder of the (GaO4)∞-tetrahedral chains. From lattice dynamical simulations we could clearly evidence that dynamic switching of the (GaO4)∞-tetrahedral chains from its R to L configuration sets in at 600 °C, thus correlating oxygen diffusion with the dynamic disorder. Oxygen ion diffusion pathways are thus constrained along the onedimensional oxygen vacancy channels, which is a different diffusion mechanism compared to that of the isostructural CaFeO2.5, where diffusion of the apical oxygen atoms into the vacant lattice sites are equally involved in the diffusion pathway. The proposed ordered room-temperature structure in I2mb is strongly supported by 17O, 45Sc, and 71Ga NMR measurements, which indicate the presence of crystallographically unique sites and the absence of local disordering effects below the phase transition. The electric field gradient tensor components measured at the nuclear sites are found to be in excellent agreement with calculated values using the WIEN2k program. The oxygen site assignment has been independently confirmed by 17O{45Sc} transfer of adiabatic populations double-resonance experiments.

A modified traveling solvent floating zone (TSFZ) technique was used to successfully grow a large size and high quality single crystal of multiferroic material YBaCuFeO 5 . This modified TSFZ growth uses a stoichiometric feed rod and pure copper oxide as the initial flux without prior knowledge of the complex phase diagram involving four elements, and the optimal flux for the growth of incongruently melt crystal is self-adjusted after a prolonged stable pulling. The wetting of the feed rod edge that often perturbs the molten zone stability was avoided by adding 2 wt% B 2 O 3 . The optimal flux concentration for the YBaCuFeO 5 growth can be extracted to be near YBaCuFeO 5 :CuO=13:87 in molar ratio. The crystal quality was confirmed by the satisfactory refinement of crystal structure of space group P 4 mm and the two consecutive anisotropic antiferromagnetic phase transitions near 455 K and 170 K.

Cation ordering in the 1322 perovskite CaCu3Fe2Nb2O12 has been investigated by synchrotron X-ray diffraction structure analysis, high-resolution electron microscopy, and magnetic measurements. All of the samples have full 1:3 ordering of Ca and Cu cations at the perovskite A-sites, but the Fe and Nb cations at the B sites show different degrees of ordering depending on the synthesis conditions. A slow-cooled sample has almost complete rock-salt-type 1:1 cation ordering at the B sites, but a rapidly cooled sample has no long-range B-cation arrangement. The ordered compound shows a large saturated magnetization (5.7 μB/formula unit (fu)) below 170 K due to the ferrimagnetism of the A′-site Cu2+ and B-site Fe3+ spins, whereas the B-site disordered form has a small magnetization (

We report on the crystal growth and magnetic property studies of layered Na2Ni2TeO6 and Na2Cu2TeO6. The former has a honeycomb layer composed of NiO6 octahedra and the latter is composed of paired CuO4 plaquettes connected through TeO6 octahedra. The 3D antiferromagnetic (AF) phase transition is defined with the peak of dχ/dT at ~27 K for Na2Ni2TeO6 and confirmed with specific heat measurement. A comparison is made between the magnetic behavior of Na2Ni2TeO6 and BaNi2V2O8, with a similar Ni honeycomb network of different centers. Na2Cu2TeO6 has been confirmed to have a spin gap of Δ/kB ~ 262 K due to spin dimerization of Cu2+S = 1/2 within each paired CuO4 plaquette.

A-site-ordered perovskite-structure oxides with Mn and V at A' and B sites, respectively, were synthesized by using a high-pressure method. Valence-state analyses revealed that the A-site substitution modulated the valence states of the Mn ions at the A' site and V ions at the B site sequentially. By changing the A-site ions from Na(+) to Ca(2+) and from Ca(2+) to La(3+), the valence distribution changed site-selectively from Na(+)Mn(2.33+)3V(4+)4O12 to Ca(2+)Mn(2+)3V(4+)4O12 and to La(3+)Mn(2+)3V(3.75+)4O12. The electrons of the A'-site Mn were localized and contributed to the magnetic properties, that is, spin-glass-like behavior in NaMn3V4O12 and antiferromagnetic behavior in CaMn3V4O12 and LaMn3V4O12. The valence electrons of the B-site V, in contrast, were delocalized, as could be seen from the low resistivity of the samples. The delocalized electrons at the B-site V did not correlate with the localized spins at the A'-site Mn.

The structural and electronic properties of BiCoO(3) under high pressure have been investigated. Synchrotron X-ray and neutron powder diffraction studies show that the structure changes from a polar PbTiO(3) type to a centrosymmetric GdFeO(3) type above 3 GPa with a large volume decrease of 13% at room temperature revealing a spin-state change. The first-order transition is accompanied by a drop of electrical resistivity. Structural results show that Co(3+) is present in the low spin state at high pressures, but X-ray emission spectra suggest that the intermediate spin state is present. The pressure-temperature phase diagram of BiCoO(3) has been constructed enabling the transition temperature at ambient pressure to be estimated as 800-900 K.

A-site-ordered perovskites La1-xNaxMn3Ti4O12 with (x = 0, 0.5, 1) were synthesized under high-pressure and high-temperature conditions, and their crystal structures and magnetic properties were investigated. Ti/Mn occupancies at the B site were also examined by using resonant X-ray diffraction, and the results confirm that they are stoichiometric with high Ti/Mn site selectivity. Substitution of Na+ for some of the La3+ changes the valence state of the A'-site Mn but not of the B-site Ti, and thus the compositions of the synthesized samples are expressed as La1-xNaxMn{(5+2x)/3}+3 Ti4+4O12. The magnetic properties change from spin-glass-like to antiferromagnetic to spin-glass-like behavior according to the valence states of A'-site Mn.

The ionic states of Cu and Mn ions and the magnetic structure in an $A$-site-ordered perovskite ${\text{BiCu}}_{3}{\text{Mn}}_{4}{\text{O}}_{12}$ were investigated by powder neutron diffraction and soft x-ray absorption and magnetic circular dichroism spectroscopy experiments. A substitution by ${\text{Mn}}^{3+}$ was found at the square-planar ${A}^{\ensuremath{'}}$ ${\text{Cu}}^{2+}$ site, leading to a composition $\text{Bi}{(\text{Cu}^{2+}{}_{0.8}\text{Mn}^{3+}{}_{0.2})}_{3}\text{Mn}^{3.6+}{}_{4}{\text{O}}_{12}$. This compound is a ferrimagnet with a collinear spin configuration below ${T}_{\text{C}}=350\text{ }\text{K}$, and the magnetic structure is stabilized by a strong ferromagnetic coupling between the ${A}^{\ensuremath{'}}$ and $B$ site Mn ions and an antiferromagnetic coupling between Cu and Mn ions, leading to a near zero net moment at the ${A}^{\ensuremath{'}}$ site.