Abstract
The effects of sintering temperature and time upon the thermoelectric properties of elements made from Bi2Te3 and its alloys by a powder metallurgical method have been studied and the mechanism of their property variations investigated.
Pressed elements from Bi2Te3 and its alloys were sintered in evacuated glass ampoules at various temperatures ranging from room temperature to those just below melting points, and their thermoelectric power α and specific resistivity ρ were measured. Besides, the Hall coefficient of some samples was measured, from which the variations in carrier concentration and carrier mobility with sintering temperature were calculated.
The result of experiments showed that properties changed roughly over three stages, that is, on sintering at temperature below 200°C at which cohesion of particles did not begin, a decrease in donors was observed. Between 200°C and 450°C, with cohesion of particles, a remarkable increase in donors was revealed. Then, above 450°C, the introduction of acceptors was observed. The increase in donors below 200°C relates to the extinction of lattice defects that occur at the time of powder production and compacting, and the activation energy for such extinction was found to be 1.2 eV. The increase in donors between 200°C and 450°C with increase in temperature is due to secondary defects that occur during cohesion of particles. In samples of low hole concentrations, the change from the P type to the N type conduction took place. The activation energy for the change was found to be 2.2 eV. From measurements of the weight loss during sintering, it has been clarified that the introduction of acceptors relates to the evaporation of Te.
