Electrical and Magnetic Properties of Strontium Substituted Lanthanum Manganate Perovskite Crystals Prepared Using Fused Salt Electrolysis

Abstract

Crystals of Sr-doped perovskite lanthanum manganates, containing 7–34 mole percent Sr have been grown by fused salt electrolysis using Cs2MoO4–MoO3 solvents in stabilized zirconia crucibles. The rhombohedral crystals grow with cubic-like habits typically with facial areas 0.25–4 mm2 on edge with the average facial area decreasing with increasing Sr content. All measured crystals with Sr contents between 11.7 and 33.6 mole percent Sr underwent transitions from a paramagnetic-insulator to a ferromagnetic-metallic state with values of Tc and TIM between 325 and >400 K (for TIM), the values increasing with Sr content. A magnetoresistance of approximately 45% at 375 K was observed for a crystal of composition Sr0.336 La0.661Mn0.997O3. The anomalously high Tc=325 K for Sr0.117La0.844Mn0.990O3 for a sample of such low Sr content is interpreted in terms of a high vacancy level on the A cation site which stabilizes the rhombohedral perovskite structure, which otherwise might have been expected to be orthorhombic type-1. The formation of Sr-doped lanthanum manganate perovskite at the cathode with the orthorhombic type-2 structure is interpreted in terms of an electrostatically assisted air oxidation mechanism.