First-principles calculations of stable local structures and electronic structures of magnesium secondary battery cathode materials,MgCo2−xMnxO4 (x = 0, 0.5), in second charged state after first discharge

Journal of Solid State Electrochemistry - The stable structures associated with the second charge of MgCo2−xMnxO4 (x = 0, 0.5), where Mg is removed from the stable first-discharge...     

Crystal structure and ferroelectric property of Bi4Si3O12-added Bi4−xSmxTi3O12

We synthesized Bi_4?xSm_xTi₃O₁₂ (x=0.55, 0.65, 0.80) and y mol% Bi₄Si₃O₁₂-added Bi_4?xSm_xTi₃O₁₂ (x=0.65; y=5, 10, 15, 20) by a solid-state reaction, and investigated a relationship between the ferroelectric properties and crystal structures in these samples. From the P–E hysteresis measurements, it was clarified that the Bi_3.35Sm_0.65Ti₃O₁₂ showed better ferroelectric properties than the others with different Sm content, and the sample began to exhibit larger remanent polarization by adding Bi₄Si₃O₁₂. In order to examine an effect of the Bi₄Si₃O₁₂-addition from a structural point of view, we measured synchrotron X-ray diffractions of the samples at room temperature and 1000 K, and analyzed their crystal and electronic structures with the Rietveld technique and the maximum entropy method. As a result, it was suggested that the Bi₄Si₃O₁₂-addition made distortions of the Ti-O₆ octahedra larger and had an effect on the TiO bond strengths.     

Oxygen nonstoichiometry and high temperature conductivity of the 2201 phase of the Bi---Sr---Cu---O superconducting oxide

The oxygen nonstoichiometry and high temperature conductivity of Bi_2.12Sr_1.86Cu_1.02O_y (2201 phase) were determined as a function of temperature (T) and oxygen partial pressure (P_O2). The dependences of conductivity on T and P_O2 were similar to those of oxygen content, and two subphases, and β, were found in such cases as 2212 and 2223 phases. From the result a close relationship was inferred between conductivity and oxygen content, and the mobility and carrier density were calculated. The carrier density of 2201 phase was smaller than those of the 2212 and 2223 phases.     

Dependence of property, crystal structure and electric conductivity on substitution content and synthetic process of T′-La2−xRExCuO4−δ (RE = Sm and Tb)

We synthesized T′-La_2−xRE_xCuO_4−δ (RE = Sm and Tb) by a co-precipitation method and sintering in vacuum at various temperatures, and investigated relationship among the crystal structure, average valence of Cu, oxygen content and electric conductivity. From X-ray diffraction measurements, it was confirmed that a main phase of the product was T′ structure (S. G.: I4/mmm) regardless of the rare earth element and its concentration, although an impurity phase was observed in a part of samples. In the samples with low average valence of Cu, the resistivity showed a metallic behavior and remarkably decreased at low temperature. Rietveld analyses using synchrotron X-ray diffractions suggested that the electric conductivity was improved by decreasing a bond length of Cu–O1 in the case of La_2−xSm_xCuO_4−δ.     

Effects of excess oxygen content on the hole-carrying CuO2-layers in Tl2(Ba1−xSrx)2Ca2Cu3Oy superconducting oxides

The effects of oxygen doping on the hole-carrying CuO₂-layers in Tl₂(Ba_1−xSr_x)₂Ca₂Cu₃O_y were studied by combined chemical and valence analysis, T_c measurements and neutron diffraction. The highest T_c is characterized by an optimal excess oxygen content, Δy, dichotomizing the under- and over-doped regions for each Sr concentration. While the average Tl valence is close to 3.0 and independent of Δy, the average Cu valence shows a linear dependence with Δy. An increase of the flatness of the CuO₂ plane, characterized by the O(2)-Cu(2)-O(2) bond angle of ∼176°, was observed at the optimal Δy.     

Average and local structure analysis of Na/Li ion-exchanged Lix(Mn,Ni,Ti)O2 using synchrotron X-ray and neutron sources

Journal of Solid State Electrochemistry - Mn-rich layered Lix(Mn,Ni,Ti)O2 was synthesized by Na/Li ion exchange of a P3-Na0.7(Mn,Ni,Ti)O2 precursor. The combined chemical analysis with the ICP-AES,...     

Relationship between average and local crystal structure and the ferroelectric properties of a Sr-Bi-Ta-Si-O ferroelectric material

We investigated the relationship between the average and local crystal structures and the ferroelectric properties of Bi₂SiO₅, Bi₄Si₃O₁₂, or Bi₂O₃ added Sr_1−xBi_2+xTa₂O₉ (x=0, 0.2) produced by a solid-state reaction. By measuring the P-E hysteresis, we found that Sr_1−xBi_2+xTa₂O₉ (x=0, 0.2) has higher P_r and E_c than SrBi₂Ta₂O₉ (SBT). P_r increased and E_c decreased by adding Bi₂SiO₅, Bi₄Si₃O₁₂, or Bi₂O₃ to Sr_1−xBi_2+xTa₂O₉. The average crystal structures were determined by the Rietveld method. On the other hand, the local structure is important, because the ferroelectric property is related to the distortion, and ferroelectric complex oxides have domains. We also investigated the local crystal structure using atomic pair distribution function (PDF) analysis. Based on the results, the bond angle variance, σ², of each TaO₆ octahedron increased by substituting Si for the Ta site. The tilting angle, α_a,α_b, of each TaO₆ octahedron increased relative to that of the average structure, and the symmetry of the TaO₆ octahedron in the local structure deteriorated in comparison to that of the average structure. This distortion and symmetry of TaO₆ contributes to the remanent polarization.     

Improvement of ethanol selectivity of silicalite membrane in pervaporation by silicone rubber coating

In order to improve the pervaporation performance of silicalite membrane, two types of silicone rubber, KE45 and KE108, were coated on the membrane surface. The initial molecular weight of KE108 is high and vulcanizing starts when it comes into contact with moisture in air, whereas the initial molecular weight of KE45 is low and vulcanizing starts when it is mixed with a catalyst. KE108 was found to be more effective than KE45 in enhancing the ethanol selectivity of silicalite membranes. A membrane coated using a 3 wt.% KE108 hexane solution showed separation factor of =125 with a total flux of 0.14 kg/m² h.     

Composition dependences of Tc,Jc, physical property and crystal structure of Bi1.8Pb0.3Sr2.0Ca0.9Y0.1Cu2.0−xMxOy (M = Zr,Zn) superconducting oxide

In this study, we focused on bulks and thin films of Bi_1.8Pb_0.3Sr_2.0Ca_0.9Y_0.1Cu_2.0O_y, and replaced Cu by Zr⁴⁺ and Zn²⁺. From the electrical conductivity measurements on the bulk samples, it was found that T_c became higher by a partial substitution of Zr⁴⁺, and exhibited a maximum value in the sample with the Zr⁴⁺ content of 0.05. On the other hand, T_c was decreased by the Zn²⁺ substitution. These results suggested that it was possible to control a carrier concentration by the Zr- and Zn-substitutions. Indeed, an average valence of the Cu, determined by a chelate titration, was changed by these substitutions. Similar tendency of the superconducting properties was also observed in the case of the film samples. In order to investigate crystal structures in detail, we measured neutron diffraction patterns, and then performed the Rietveld analysis. As a result, it was clarified that the (Cu, Zr)–O2 layers became flat by the Zr-substitution. Such a structure change may be one of the reasons why the substitution improved the superconducting properties.