Improvement of thermoelectric properties of Cu2Se superionic thermoelectric materials with B4C micro inclusions

The work aimed to obtain Cu 2 Se copper selenide with B 4 C boron carbide micro inclusions with improved thermoelectric properties compared to pure copper(I) selenide. Both Cu 2 Se and B 4 C were synthesized and then mixed and the powders with composition (Cu 2 Se) 1-x (B 4 C) x , where x = 0, 0.005, 0.01, 0.02 and 0.04 were sintered using the SPS technique. Density of sinters measured by hydrostatic method decreases from ρ = 6.72 g·cm -3 for x = 0 to ρ = 6.55 g·cm -3 for x = 0.04. The phase and chemical compositions were examined using X -ray diffraction (XRD), Scanning electron microscopy (SEM), which showed that the obtained boron carbide powder has grain sizes in the range of about 0.5 – 1.3 μm and in the sinters their sizes are in the range of approx. 0.5 – 2.5 μm. Transmission electron microscopy (TEM) showed multiphase nature of the B 4 C material. Thermoelectric homogeneity was investigated by scanning thermoelectric microprobe (STM), which showed a unimodal distribution of the Seebeck coefficient for samples without and with B 4 C addition Measurements of thermoelectric transport properties, i.e. electrical conductivity, Seebeck coefficient and thermal conductivity were carried out in the temperature range from 300 to 965 K. Thermal conductivity determined based on thermal diffusivity measurement and specific heat determined by LFA method for all samples with B 4 C addition are lower than in the case of pure Cu 2 Se. The ZT parameter was determined for all samples and the highest value of ZT max = 1.31 was obtained for a sample with composition (Cu 2 Se) 0.98 (B 4 C) 0.02 which is 20 % higher than for pristine Cu 2 Se ( ZT max = 1.09).