Structure-property relations of Ag2-3xBixI2 have been revealed.

Room-temperature multiferroism in polycrystalline antiferromagnetic Fe perovskites is reported for the first time. In the perovskite-type oxides RE 1.2 Ba 1.2 Ca 0.6 Fe 3 O 8 (RE = Gd, Tb), the interplay of layered ordering of Gd(Tb), Ba, and Ca atoms with the ordering of FeO 4 -tetrahedra (T) and FeO 6 -octahedra (O) results in a polar crystal structure. The layered structure consists of the stacking sequence of RE/Ca-RE/Ca-Ba-RE/Ca layers in combination with the TOOT sequence in a unit cell. A polar moment of 33.0 μC/cm 2 for the Gd-oxide (23.2 μC/cm 2 for the Tb one) is determined from the displacements of the cations, mainly Fe, and oxygen atoms along the b-axis. These oxides present antiferromagnetic ordering doubling the c-axis, and the magnetic structure in the Tb-compound remains up to 690 K, which is one of the highest transition temperatures reported in Fe perovskites.

Optically generated excitonic states (excitons and trions) in transition metal dichalcogenides are highly sensitive to the electronic and magnetic properties of the materials underneath. Modulation and control of the excitonic states in a novel van der Waals (vdW) heterostructure of monolayer MoSe2 on double‐layered perovskite Mn oxide ((La0.8Nd0.2)1.2Sr1.8Mn2O7) is demonstrated, wherein the Mn oxide transforms from a paramagnetic insulator to a ferromagnetic metal. A discontinuous change in the exciton photoluminescence intensity via dielectric screening is observed. Further, a relatively high trion intensity is discovered due to the charge transfer from metallic Mn oxide under the Curie temperature. Moreover, the vdW heterostructures with an ultrathin h‐BN spacer layer demonstrate enhanced valley splitting and polarization of excitonic states due to the proximity effect of the ferromagnetic spins of Mn oxide. The controllable h‐BN thickness in vdW heterostructures reveals a several‐nanometer‐long scale of charge transfer as well as a magnetic proximity effect. The vdW heterostructure allows modulation and control of the excitonic states via dielectric screening, charge carriers, and magnetic spins.

The paraelectric cubic structure of (Bi 1/2 Na 1/2 )TiO 3 was analyzed precisely by high-energy synchrotron radiation X-ray powder diffraction measurement and the maximum entropy method (MEM)/Rietveld method. The o100p-favored rotator-like thermal behavior of the Bi ion was observed. The o100p off-centering of Bi led to the Bi-O distance of >2.5 Å that was shorter than the average Bi-O distance in the structure of the Bi on-centered model. The off-centering of Bi can be attributed to the orbital hybridization between the Bi and O ions.

Modulated structure of incommensurate composite crystal (Sr 2 Cu 2 O 3 ) 0.70 CuO 2 , ''Sr 14 Cu 24 O 41 ,'' has been investigated by single-crystal x-ray-diffraction method using centrosymmetric (3ϩ1)-dimensional superspace group. In (Sr 2 Cu 2 O 3 ) 0.70 CuO 2 , displacive modulation of O atom in the CuO 2 chain is fairly large. Considering the modulation of bond angles, it has been found that the Cu-O bond in the CuO 2 chain is tilting toward the Cu 2 O 3 ladder in order that the O atom in the chain plays as apical oxygen for the CuO 4 square in the ladder. The bond-valence sum ͑BVS͒ method has been applied to investigate the hole distribution in the modulated structure of (Sr 2 Cu 2 O 3 ) 0.70 CuO 2 . It is indicated that the valence of Cu atom in the Cu 2 O 3 ladder is ϩ2.04, where about 0.03 holes are certainly transferred from the CuO 2 chain through the modulated O atom in the CuO 2 . The BVS calculation has demonstrated that almost all of the holes are prepared in the CuO 2 chain by the large modulation of the Cu-O bond. Cu atoms in the modulated CuO 2 chain have been proved to form hole-ordered structure with next-nearest-neighbor Cu 2ϩ ions separated by Cu 3ϩ ion on the Zhang-Rice singlet site. The periodicity of the hole-ordered structure is five times of the average CuO 2 lattice along the crystallographic c axis, which is compatible with the spin-dimerized state at low temperature. The new model of the two-dimensional hole-ordered structure in the CuO 2 plane has been obtained by the BVS calculation. Furthermore, the two-dimensional configuration of the spin dimers has been successfully derived from the holeordered structure in the CuO 2 plane. It has been concluded that the valences of Cu atoms both in the Cu 2 O 3 ladder and in the CuO 2 chain are well controlled by the modulated O atom in the CuO 2 chain.

Materials which show novel thermal properties can be used to make highly efficient and environmentally friendly energy systems for thermal energy storage and refrigeration through caloric effects. An A-site-ordered quadruple perovskite-structure oxide, NdCu 3 Fe 4 O 12 , is found to release significant latent heat, 25.5 kJ kg −1 (157 J cc −1 ), at the intersite-charge-transfer transition temperature near room temperature. The transition is first-order and accompanied by an unusual magnetic ordering and a large negative-thermalexpansion-like volume change, and thus, it causes a large entropy change (84.2 J K −1 kg −1 ). The observed entropy change is comparable to the largest changes reported in inorganic solid materials, and more importantly, it is utilized through a colossal barocaloric effect. The adiabatic temperature change by applying 5.1 kbar pressure is estimated to reach 13.7 K, which means efficient refrigeration can be realized through this effect.

Dependence on lithium-ion batteries for automobile applications is rapidly increasing. The emerging use of anionic redox can boost the energy density of batteries, but the fundamental origin of anionic redox is still under debate. Moreover, to realize anionic redox, many reported electrode materials rely on manganese ions through π-type interactions with oxygen. Here, through a systematic experimental and theoretical study on a binary system of Li 3 NbO 4 −NiO, we demonstrate for the first time the unexpectedly large contribution of oxygen to charge compensation for electrochemical oxidation in Ni-based materials. In general, for Ni-based materials, e.g., LiNiO 2 , charge compensation is achieved mainly by Ni oxidation, with a lower contribution from oxygen. In contrast, for Li 3 NbO 4 −NiO, oxygen-based charge compensation is triggered by structural disordering and σ-type interactions with nickel ions, which are associated with a unique environment for oxygen, i.e., a linear Ni−O−Ni configuration in the disordered system. Reversible anionic redox with a small hysteretic behavior was achieved for LiNi 2/3 Nb 1/3 O 2 with a cation-disordered Li/Ni arrangement. Further Li enrichment in the structure destabilizes anionic redox and leads to irreversible oxygen loss due to the disappearance of the linear Ni−O−Ni configuration and the formation of unstable Ni ions with high oxidation states. On the basis of these results, we discuss the possibility of using σ-type interactions for anionic redox to design advanced electrode materials for highenergy lithium-ion batteries.

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