Cooling rate dependence of microstructure and thermoelectric properties of AgPb18SbTe20 compounds

AgPb₁₈SbTe₂₀ samples were prepared by cooling from melts at three different rates as quenching, furnace cooling and controlled slow cooling rate of 10degC /h, and the correlation between cooling rates and samples microstructure and thermoelectric properties were discussed. Experimental results show that cooling rates influence significantly the microstructure and thermoelectric properties of the samples. As the cooling rate increased, an Ag-Sb-rich second phase occurred. Samples carrier concentration and electrical conductivity decrease with increased cooling rates and all samples measured have a negative Seebeck coefficient showing n-type conduction. At room temperature, the power factor of the slow cooled sample is 100 times that of the quench samples, and the ZT value of furnace cooled samples is much higher than that of the quenched samples. This results may explain why the samples several researchers prepared by different synthesis processes show very different ZT values.