ELECTRICAL AND MAGNETIC PROPERTIES OF STRONTIUM SUBSTITUTED LANTHANUM MANGANATE PEROVSKITE CRYSTALS PREPARED USING FUSED SALT ELECTROLYSIS

摘要

Crystals of Sr-doped perovskite lanthanum manganates, containing 7-34 mol% Sr have been grown by fused salt electrolysis using Cs2MoO4-MoO3 solvents in stabilized ZrO2 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 mol% 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 Sr0.336La0.661Mn0.997O3. 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. 42 refs.