Effects of Ni Magnetic Nanoparticles on Thermoelectric Properties of n -Type Bi 2 Te 2.7 Se 0.3 Materials

A series of n -type x %Ni/Bi 2 Te 2.7 Se 0.3 ( 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 Bi 2 Te 2.7 Se 0.3 matrix and prone to react with Te to form NiTe 2 phase. Room-temperature charge transport measurements indicated that the conduction behavior of the x %Ni/Bi 2 Te 2.7 Se 0.3 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 Bi 2 Te 2.7 Se 0.3 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 Bi 2 Te 2.7 Se 0.3 matrix, suggesting that much higher thermoelectric properties could be obtained if an appropriate sintering method which can suppress this reaction were adopted.