Features of microstructure and thermoelectric properties of the cermet composites based on grained Bi2Te3 matrix with locally-gradient Ni@NiTe2 inclusions

Abstract

Starting Bi2Te3 and Ni powders were spark-plasma-sintered (SPS) to prepare thermoelectric cermet composites consisting of thermoelectric Bi2Te3 matrix with different content, x, of ferromagnetic Ni filler (x = 0.00, 0.50, 0.85, 1.25 and 1.50 at. %). Grained Bi2Te3 matrix of composites is texturing under sintering. Texturing degree is x-dependent that is attributed to ability of Ni particles act as lubricant. New trigonal NiTe2 phase is formed under SPS-process. The Ni and NiTe2 phases correspond to filler Ni@NiTe2 (“core”-“shell”) inclusions. Forming these inclusions is originated from chemical interaction between Bi2Te3 and Ni during SPS-process. A Ni→NiTe2 reaction is accelerated with increasing x that results in growing Ni@NiTe2 inclusions and increasing fraction of shell. Thermoelectric properties of composites are x-dependent that is due to non-monotonic changes in texturing degree, size of the inclusions and concentration of majority carriers with increasing x. Thermoelectric figure-of-merit of composites is remarkably enhancing as compared to that of Bi2Te3 matrix.