Studies on Sr substituted lanthanum indate as mixed ionic conductor

Sr substituted LaInO₃ compounds have been prepared by the conventional solid state reaction method. The as-prepared samples are characterized by X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), differential thermal analysis (DTA), thermal expansion coefficient (TEC), and impedance spectroscopy. The XRD analysis of LSI 20 shows the formation of single phase La_0.9Sr_0.1InO_2.95 compound. However, the higher substitution of Sr²⁺ for La³⁺ leads to the formation of secondary insulating phase, i.e., SrIn₂O₄. Sr substitution leads to anionic vacancy which is the possible mechanism for ionic conduction in the given system. Reitveld refinement confirms orthorhombic phase formation in all the samples except LSI 23 (La_0.77Sr_0.23InO_2.89) which is well fitted monoclinic phase. TEC is nearly 9.1 × 10⁻⁶ °C⁻¹ in the range of 500–1000 °C in LSI 20 sample. The ionic conductivity is 0.11 mS cm⁻¹ at 800 °C in single phase LSI 20 sample. The solid solubility limit is x = 0.20 which is higher than earlier reported values for similar systems.