Transport Properties of the Layered Transition Metal Oxypnictide Sr₂ScMPO₃ with MP layers (M =Mn, Ni and Co_0.5Fe_0.5)

Polycrystalline samples of novel oxypnictides, Sr₂ScMPO₃, with MP layer (M = Mn, Ni and Co_0.5Fe_0.5) were synthesized, and their resistivities and Seebeck coefficients were measured. Sr₂ScMPO₃ crystallizes in a stacked, layered structure comprised of a ThCr₂Si₂- type MP layer alternating with a K₂NiF₄-type Sr₂ScO₃ layer. Sr₂ScMnPO₃ is an insulator at room temperature. The resistivities (ρ) of Sr₂ScNiPO₃ and Sr₂ScCo_0.5Fe_0.5PO₃ decrease with decreasing temperature like a metal. The Seebeck coefficients (S) of these materials are negative at room temperature. For Sr₂ScNiPO₃, S initially decreases slightly with decreasing temperature, and increases with decreasing temperature below 50 K. However, for Sr₂ScCo_0.5Fe_0.5PO₃, S increases with decreasing temperature, and attains to a positive value below 270 K