Electrical and thermal properties of hot pressed (Nd0.5Gd0.5)Se1.50-x, where x=0.01, 0.02

Rare earth selenides, based on the composition (Nd0.5Gd0.5)Se1.50-x where 0 .005 less than or equal tox less than or equal to0.030, were prepared by va por phase reaction, melting, and hot pressing. The transport properties of electrical resistivity, Seebeck coefficient, and thermal diffusivity were c haracterized between 300 and 1300 K. In addition, carrier concentration and mobility were measured at 300 K. Chemical composition and homogeneity were determined on several samples by electron microprobe and atomic emission s pectroscopy. Partial substitution of Nd for Gd was found to stabilize the h igh temperature gamma (Th3P4-type) phase. This system is characterized by a low thermal conductivity, the temperature dependence of which indicates mi xed scattering. Analysis of the Seebeck and carrier concentration data by a single band conduction model suggests the existence of a heavy electron ba nd, responsible for the large thermopower in this system. Electrical resist ivity and Seebeck coefficient data were combined in a Jonker analysis to de termine a maximum power factor, (S-2/rho), of 5.4 muW/cm degrees C2, corres ponding to a resistivity of 5.5 Omega cm and a Seebeck coefficient of -172. 3 muV/degreesC. (C) 2001 American Institute of Physics.