Composition and temperature dependent structural investigation of the perovskite-type sodium-ion solid electrolyte series Na1/2−xLa1/2−xSr2xZrO3.

Owing to their vast chemical and structural flexibility, crystalline perovskite-type metal oxides (AB O 3) are amongst the most promising solid electrolytes for use in all-solid-state batteries for large scale energy storage applications. The perovskite-type sodium-ion solid electrolyte series Na 1/2- x La 1/2- x Sr 2 x ZrO 3 have the highest reported ionic conductivities, and we re-examine their room temperature crystal structures using X-ray and high-resolution neutron powder diffraction. In contrast to a previous report, four members of the series, x = 1/16, 1/8, 1/6, and 1/4, were found to adopt orthorhombic symmetry with the space group Pbnm. Variable temperature neutron diffraction data (room temperature to 1100 °C) were used to probe temperature-dependent structural changes for the member of the series with the highest reported ionic conductivity (x = 1/6). A phase transition from orthorhombic Pbnm to tetragonal I 4/ mcm was identified at 800 °C. • The crystal structures of the perovskite-type sodium-ion solid electrolyte series Na 1/2- x La 1/2- x Sr 2 x ZrO 3 were determined. • The x = 1/16, 1/8, 1/6, and 1/4 members adopt orthorhombic symmetry in space group Pbnm instead of cubic P 2 1 3 symmetry. • A phase transition to tetragonal I 4/ mcm at 800 ◦C was found for Na 1/3 La 1/3 Sr 1/3 ZrO 3 using neutron powder diffraction data. • Enhanced understanding of the structure-property relationship informs chemical and structural modifications. [ABSTRACT FROM AUTHOR]