Effect of Spark Plasma Sintering Temperature on Thermoelectric Properties of Grained Bi1.9Gd0.1Te3 Compound

Patterns in changes of the microstructure (grain structure) and the thermoelectric properties of the n-type grained Bi1.9Gd0.1Te3 compound, spark-plasma-sintered at different temperatures (TS = 690, 720, 735, 750, 780, and 810 K), have been studied in detail. All the samples studied were highly textured along the 001 direction parallel to the pressing direction, that resulted from preferential orientation of the grains. Orientation factor characterizing a texturing degree and estimated from XRD patterns happened to be weakly TS-dependent. Average grain size measured along the SPS pressing direction was far less as compared to that measured in the perpendicular direction. The thermoelectric properties measured for the perpendicular direction happened to be better than the same properties, but taken for the parallel direction. Of the samples sintered at different temperatures, the highest value of the thermoelectric figure-of-merit equal to ~0.73 for the perpendicular measuring orientation was found for the sample sintered at TS = 750 K. This sample is characterizing by the maximum power factor and the low enough thermal conductivity.