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 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 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 Sr_0.336 La_0.661Mn_0.997O₃. The anomalously high T_c=325 K for Sr_0.117La_0.844Mn_0.990O₃ 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.