Investigation Of Isothermal Sections Of Pb-Sb-Te And Sn-Sb-Te Systerm

Thermoelectric devices are generally made from thermoelectric materials and which has obviously outstanding advantages,such as non-pollution,being silent,reliability,long life,and long period of operation without attention,and all of these advantages lead to a wide range of applications.The phase diagrams of the thermoelectric materials such as lead telluride(PbTe-)and tin telluride(SnTe-)based systems,can be used in thermoelectric R&D in furture.The isothermal sections of the Pb-Sb-Te ternary system at 500℃and the Sn-Sb-Te ternary system at 200℃ have been determined and discussed.The alloy samples are investigated by X-ray diffraction analysis(XRD),scanning electron microscope(SEM)and energy-dispersive X-ray spectroscopy(EDS)techniques.The heat capacity of the Pb-Sb-Te ternary system is measured by differential scanning calorimeter(DSC)using the small temperature steps method.Some important results are listed as follow,(1)The isothermal section of the Pb-Sb-Te ternary system at 500℃has been established.It is composed of five single-phase regions,four two-phase regions and five three-phase regions.The solubility of Sb in PbTe phase is 2.03 at.%at 500℃,and the solubility of Pb in Sb2Te3 is up to 7.17 at.%.Moreover,the Pb2Sb6Te11 ternary compound has not observed in present work.(2)The isothermal section of the Sn-Sb-Te ternary system at 200℃was also established.It is consisted of three single-phase regions,five two-phase regions and five three-phase regions.The ternary compound SnSb2Te4 was observed in Sn-Sb-Te ternary system at 200℃.The existence of SnSb2Te4 ternary compound was confirmed.(3)We measure and calculate the heat capacity of the Pb-Sb-Te ternary system between 340.15 K and 543.15 K with the relaxation technique using a commercial DSC.The values of the heat capacity increase monotonically with temperature increase and depend on the proportion of Sb/Te.It can be seen that the heat capacity has a maximum value when the proportion of Sb/Te reaches to 1/2.The enhanced thermoelectric properties may be due to the low thermal conductivities which are induced by doping of Sb2Te3 and much smaller than that reported for bulk PbTe.