Preparation And Thermoelectric Properties Of P-type Skutterudite Materials With Substitution Of Germanium And Tin For Sb

Skutterudite is the most promising thermoelectric (TE) material in the moderatetemperature range. The highest ZT value of n-type skutterudite materials has reached1.7, but the ZT values of p-type skutterudite materials are still hovering at a level ofaround1.0. Obtaining p-type skutterudite materials with comparable ZT values tothose of n-type skutterudite materials is the key factor for improving the conversionefficiency of skutterudite TE devices. How to improve the ZT values of p-typeskutterudite materials is the bottleneck problem urgently to be solved in theinternational TE materials field. In this thesis, three series of p-type TE materials withnominal composition Fe0.4Co3.6Sb12-xSnx(0≤x≤0.4, Δx=0.1), Fe0.4Co3.6Sb12-xGex(0≤x≤0.4, Δx=0.1) and Fe0.4Co3.6Sb11.85Sn0.15-xGex(0≤x≤0.15, Δx=0.03) have beenprepared by a combination of melt quenching and spark plasma sintering. The effectsof Sn, Ge single substitution and (Ge,Sn) double substitution on the phasecomposition, microstructure and TE properties of Fe0.4Co3.6Sb12were investigated.The main results are as follows:The main phase of all Fe0.4Co3.6Sb12-xSnxsamples was skutterudite, asingle-phase skutterudite material was obtained in the samples with x≤0.2, and trace(Fe,Co)Sb2was detected in the samples with x>0.2. Grain growth was detected in thesamples with x>0.2. The TE transport measurements demonstrated that electricalconductivity decreased and Seebeck coefficient increased with increasing the x in therange of0~0.2, while the electrical conductivity increased and Seebeck coefficientdecreased in the samples with x>0.2. The lattice thermal conductivity wasconsiderably reduced by the substitution of Sn for Sb, and the lowest value of latticethermal conductivity of the Fe0.4Co3.6Sb11.8Sn0.2sample was only about1.68W·m-1·K-1at800K. The highest ZT value of0.36was obtained at800K for theFe0.4Co3.6Sb11.9Sn0.1sample, increased by12.5%as compared to that of theFe0.4Co3.6Sb12.The main phase of all Fe0.4Co3.6Sb12-xGexsamples was skutterudite, a single-phase skutterudite material was obtained in the samples with x≤0.1, trace(Fe,Co)Sb2was detected in the sample with x=0.2, and impurity phases such as(Fe,Co)Sb2,(Fe,Co)Sb, and (Fe,Co)3Ge2were detected in the samples with x>0.2.Grain growth was detected in the samples with x≥0.2. The TE transportmeasurements demonstrated that the electrical conductivity decreased and theSeebeck coefficient increased with increasing the x in the range of0~0.1, while theelectrical conductivity increased and the Seebeck coefficient decreased in the sampleswith x≥0.2. The lattice thermal conductivity was considerably reduced by thesubstitution of Ge for Sb, and the lowest value of lattice thermal conductivity of theFe0.4Co3.6Sb11.9Ge0.1sample was only about1.67W·m-1·K-1at800K. The highest ZTvalue of0.44was obtained at800K for the Fe0.4Co3.6Sb11.9Ge0.1sample, increased by25.7%as compared to that of the Fe0.4Co3.6Sb12.The main phase of all Fe0.4Co3.6Sb11.85Sn0.15-xGexsamples was skutterudite, asingle-phase skutterudite material was obtained in the samples with x≤0.09, and trace(Fe,Co)Sb2was detected in the samples with x≥0.12. Grain size did not changesignificantly in all samples. The TE transport measurements demonstrated that theelectrical conductivity did not change significantly, while the Seebeck coefficientslightly increased with increasing the x in the range of0~0.09; the electricalconductivity increased and the Seebeck coefficient decreased in the samples withx≥0.12. The lattice thermal conductivity was considerably reduced by doublesubstitution of (Ge,Sn) for Sb, and the lowest value of lattice thermal conductivity ofFe0.4Co3.6Sb11.85Sn0.09Ge0.06sample was only about1.56W·m-1·K-1at800K. Thehighest ZT value of0.40was obtained at800K for the Fe0.4Co3.6Sb11.85Sn0.06Ge0.09sample, compared to the Sn and Ge single substituted samples, the ZT value increasedby14.3%and25.0%respectively.