Electrical and magnetic properties of new rhodium perovskites: La2MRhO6, M = Cr, Fe, Cu

The compositions La2FeRhO6, La2CrRhO6, La2CuRhO6 were prepared for the first time, and their electrical and magnetic properties were determined. Known La2MnRhO6, La2CoRhO6, and La2NiRhO6 were also prepared and their properties determined for comparison. All six phases have the orthorhombic perovskite structure. Electrical resistivity measurements as a function of temperature indicate that all phases are semiconducting. Seebeck measurements show that all are p-type conductors. Magnetic measurements indicate general antiferromagnetic interactions for all compositions, although evidence for weak ferromagnetism is found in the case of La2CrRhO6 and La2FeRhO6. The oxidation state of M cation appears to be close to 3+ for Fe and Cr, and a mixture of 2+/3+ for Cu. A favorable combination of electrical conductivity and Seebeck coefficient results in a relatively high thermoelectric power (1.11 W/m-K2 at ∼575 K) factor for La2CuRhO6.