Syntheses, structures, and ionic conductivities of perovskite-structured lithium–strontium–aluminum/gallium–tantalum-oxides

• Published in: Journal of solid state chemistry 2015-05, Vol.225, p.431-437
• Main Authors: Phraewphiphat, Thanya, Iqbal, Muhammad, Suzuki, Kota, Matsuda, Yasuaki, Yonemura, Masao, Hirayama, Masaaki, Kanno, Ryoji
• Format: Article
• Language: English
• Subjects: ALUMINIUM COMPOUNDS; BOND LENGTHS; CATIONS; DIFFUSION; GALLIUM COMPOUNDS; GALLIUM IONS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; IONIC CONDUCTIVITY; LITHIUM COMPOUNDS; Lithium ionic conductor; Lithium solid electrolyte; NEUTRON DIFFRACTION; Neutron diffraction analysis; OXYGEN; Perovskite; SOLID ELECTROLYTES; SOLID SOLUTIONS; STRONTIUM COMPOUNDS; STRUCTURAL MODELS; SYNTHESIS; TANTALUM IONS; TANTALUM OXIDES; VACANCIES
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2015.01.007

The ionic conductivities of new perovskite-structured lithium–strontium–aluminum/gallium–tantalum oxides were investigated. Solid solutions of the new perovskite oxides, (LixSr1−x)(Al(1−x)/2Ta(1+x)/2)O3 and (LixSr1−x)(Ga(1−x)/2Ta(1+x)/2)O3, were synthesized using a ball-milled-assisted solid-state method. The partial substitution of the smaller Ga+3 for Ta+5 resulted in new compositions, the structures of which were determined by neutron diffraction measurements using a cubic perovskite structural model with the Pm−3m space group. Vacancies were introduced into the Sr(Li) sites by the formation of solid solutions with compositions (LixSr1−x−y☐y)(Ga[(1−x)/2]−yTa[(1+x)/2]+y)O3, where the composition range of 0≤y≤0.20 was examined for x=0.2 and 0.25. The highest conductivity, 1.85×10−3Scm−1 at 250°C, was obtained for (Li0.25Sr0.625☐0.125)(Ga0.25Ta0.75)O3 (x=0.25, y=0.125). Enhanced ionic conductivities were achieved by the introduction of vacancies at the A-sites. Novel lithium-conducting oxides with the cubic perovskite structure (LixSr1−x−y☐y)(Ga[(1−x)/2]−yTa[(1+x)/2]+y)O3 provide a specific solid-solution region with various x and y values, exhibiting the highest ionic conductivity (1.85Scm−1 at 250°C) for (Li0.25Sr0.625☐0.125)(Ga0.25Ta0.75)O3 (x=0.25, y=0.125 in (LixSr1−x−y☐y)(Ga[(1−x)/2]−yTa[(1+x)/2]+y)O3). The vacancies (☐) introduced into the A-sites contribute to the enhancement of lithium diffusion in the perovskite structure because of the enlargement of the bottleneck size and suppression of the interaction between lithium and oxygen. [Display omitted] •The perovskite-structured novel Li–Sr–Al/Ga–Ta oxides were investigated.•The Ga cation offers a larger bottleneck by increasing the BO bond length.•The greater conductivity was observed upon Ga-containing perovskite.•The ionic conductivity was improved by the introduction of vacancies into A-site.