Synthesis And Properties Of Silicides Thermoelectric Materials

Thermoelectric materials are famous for converting heat energy to electricity and visas versdirectly. This paper synthesis SiGe alloys by high energy ball milling and induction hot press, weprepare Mg-Si-Sn melting samples with induced melting, and synthesis the hot pressed samles withinduced hot press. Samples include Ga doped SiGe alloys and Sb doped SiGe alloys, Sb dopedMg2Si1-xSnxsolid solution, rare earth element La and Bi doped Mg2Si1-xSnxstate solution.Property characterization shows that Ga-doping SiGe alloys leads to p-type conduction, whileSb-doping leads to n-type. SiGe alloys with Ga-doping have good thermoelectric properties. Thedimensionless thermoelectric figure of merit (ZT) of the sample with the nominal compositionSi80Ge18Ga2is0.51at805°C. But it is difficult to control the Ga content in SiGe alloys.Thermoelectrical propertivities maybe improved by precisely control the content of doping element,if we can make it. Although the Sb-doping SiGe alloys have much lower thermoelectricalpropertivities than P-doping SiGe alloy, there’s much room for improving. The nominalcomposition Si80Ge17Sb3has the maximum ZT value0.51at708℃. Both the Ga-doping SiGe alloyand Sb-doping SiGe alloy, the grain size decreases dramatically with increasing mill time.The XRD spectra reveal that all of the doping element (Sb, Bi and La) can dissolve inMg2Si1-xSnxalloy form substitutional solid solution. The nominal compositionMg2Si0.6Sn0.3927Sb0.0075has the highest ZT value0.827at412℃in Sb-doping melting samples.However, it is not so good for its hot pressed samples. The phase analysis reveal that it may becaused by the residual Si and Sn. Thermoelectric properties of the hot pressed sample with thenominal composition Mg2Si0.7Sn0.2927Sb0.0075has little increase while others present a significantlydecreased after annealing. And the hot pressed sample with nominal compositionMg2Si0.5Sn0.4927Sb0.0075has the highest ZT value at609℃. Melting samples of Mg2Si1-xSnxmatrixthermoelectric materials with La and Bi doped present multiphase coexistence from the XRDspecture. Only nominal composition La0.005Mg1.995Si0.6Sn0.39Bi0.01forms a full solid solution in allhot pressed samples. But it seems to the performance there’s no obvious difference between singlephase and multiphase. The electrical conductivity of melting samples with two elements doped ishigher than the samples with one element doped, but its thermal conductivity is lower than the oneelement doped. The nominal composition La0.01Mg1.99Si0.4Sn0.59Bi0.01has the maximum ZT~1.05at410℃. The thermal conductivity of hot pressed samples live up to our expentation, the thermalconductivity of the sample with the nominal composition La0.005Mg1.995Si0.4Sn0.59Bi0.01is1.30Wm-1K-1at room temperature and at209℃it decreases to1.17Wm-1K-1. However, compared with the melting samples, the hot pressed samples had much lower electrical conductivity as thethermoelectric propertivities. The maximum ZT value is0.79near409℃for the hot pressed samplewith the nominal composition La0.005Mg1.995Si0.4Sn0.59Bi0.01.