Effect of densification technique and carrier concentration on the thermoelectric properties of n-type Cu1.45Ni1.45Te2 ternary compound

Abstract

Cu_1.45Ni_1.45Te₂ ternary compound was synthesized by solid-state ball-milling method and densified via spark plasma sintering (SPS) and cold-pressing with annealing (CPA) techniques. The effect of densification techniques on the thermoelectric properties was studied. SPS sample showed negative Seebeck coefficient values for the entire temperature range, while CPA sample changed the sign of the Seebeck coefficient above 573 K from n-type to p-type. The electrical conductivity was higher for SPS sample than for CPA sample for the entire temperature range. Hence, SPS sample exhibited 167% increased zT when compared to CPA sample. It is confirmed that the SPS technique is more suitable to obtain a high zT value than the CPA technique for n-type Cu_1.45Ni_1.45Te₂ sample. Also, the effect of carrier concentration was studied and the change in the carrier concentration was done by Se-doping. From a series of thermoelectric measurements, it was found that the undoped sample exhibited a high zT of about 0.004 at 400 K and the Se-doped sample exhibited a zT of 0.001 at 750 K. It means that Se-doping mainly influences the shifting of the operating temperature of TE performance from room temperature range to mid-temperature range. The formation of n-type TE material was realized due to the delocalization of electron density on Te-ions, which compensate the Cu-vacancies resulting in the n-type conduction behaviour. Se-doping modifies the reaction of Te-ions with cations affecting the delocalization of electron density, which shifts the conduction type from n-type to p-type behaviour.