Transport and thermoelectric properties of Sr3(Ti0.95R0.05)2O7 (R = Ta, Nb, W) oxides

The Sr-3(Ti0.95R0.05)(2)O-7 (R = Ta, Nb, W) polycrystalline compounds were fabricated, and their transport and thermoelectric properties were investigated. The results indicate that at T> 300K electrical resistivity rho for all the doped compounds increases monotonically with temperature, and basically can be described by a relation rho alpha T-M at T> similar to 650 K, with M = 1.39, 1.66, and 1.77 for R = Ta, Nb, and W, respectively, implying that at the high temperatures the acoustic phonon scattering dominates the scattering process. Although the resistivity rho of Sr-3(Ti0.95R0.05)(2)O-7 exhibits a metallic-like behavior at the temperature as low as 5K, a transition from metallic state (d rho/dT> 0) to semiconductor-like state (d rho/dT< 0) was observed at a critical low temperature similar to 41K and similar to 79K for R = Nb and W, respectively. At T< similar to 22 K, similar to 57 K, and similar to 80 K, a relation of sigma alpha T-1/2 (here conductivity sigma = 1/rho) holds for the doped compounds with R = Nb, Ta, and W, respectively, suggesting that at the low temperatures the main transport mechanism is electron-electron interaction due to the presence of disorder induced by the dopants. The thermoelectric figure of merit (ZT) for Ta-doped compound increases more steeply with increasing temperature among the three compounds and reaches 0.066 at 1000 K. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4769787]