Electrical and magnetic properties of strontium substituted lanthanum manganate perovskite crystals prepared using fused salt electrolysis

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 mm(2) 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 T-c and T-IM between 325 and > 400 K (for T-IM), 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 T-c = 325K 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. (C) 1999 Academic Press.