Effects of Ni Magnetic Nanoparticles on Thermoelectric Properties of n-Type Bi2Te2.7Se0.3 Materials

A series of n-type x%Ni/Bi2Te2.7Se0.3 (x = 0, 0.1, 0.4, 0.7, and 1.0) magnetic nanocomposite thermoelectric materials have been fabricated by the combination of ultrasonic dispersion, hydrothermal homogenization, and spark plasma sintering. X-ray diffraction analysis indicated that the Ni nanoparticles were unstable in the Bi2Te2.7Se0.3 matrix and prone to react with Te to form NiTe2 phase. Room-temperature charge transport measurements indicated that the conduction behavior of the x%Ni/Bi2Te2.7Se0.3 magnetic nanocomposite changed from n-type (electrons) to p-type (holes) with increasing Ni content, due to the formation of a p-type region in the Bi2Te2.7Se0.3 matrix by the reaction of Ni with Te during the sintering process. The reaction of Ni nanoparticles with Te seriously degraded the electrical and thermal transport properties of the Bi2Te2.7Se0.3 matrix, suggesting that much higher thermoelectric properties could be obtained if an appropriate sintering method which can suppress this reaction were adopted.