Sturctures And Thermoelectric Properties Of Doped-Ga₂Te₃-based Semiconductors

Ga2Te3is one of the typical defects (space) zinc-blende cubic crystalstructure compounds (Eg=1.65eV) among the AIIIVI2B3type wide bandgapsemiconductor materials, whose space group is F-43m. Due to the inherertperiodic superlattice vacancy planes, there is a huge transport resistance tocarriers and phonons, thereby the intrinsic Ga2Te3material has poor electricalconductivity and low lattice thermal conductivity. In this light, we aim atinvestigating the relationship between the composition, structure andthermoelectric performance by using heat treatment and substitution of elementsor compounds in Ga2Te3, and the detailed achievements have been summarizedfollows:1. On the basis of the previous studies, we have confirmed the preferentialoccupation of Cu in the Ga lattice by calculating the formation energy andRietveld refinement, which disturbs the vacancy path. At the meantime werevealed that the sample annealed for30days has generated Heaven rain-shapeddiscontinuous vacancy planes which can effectively reduce the lattice thermalconductivity (kL), thus accounting for the remarkable improvement inthermoelectric performance with the maximum dimensionless figure of merit (ZT)(0.41), which is about2.5times that of intrinsic Ga2Te3. However, with theannealing time extending from30days to95days, there is a gradualenhancement in kLand limited improvement in thermoelectric property, which iscaused by the amalgamation or restructuring of the discontinuously vacancyplanes.2. We have prepared three kinds of Cd-containing compounds：Ga2-xCd1.5xTe3(x=0.025,0.05,0.1,0.2)，Ga2-xCdxTe3(x=0.05,0.1,0.15,0.2) andCd(3-3m)Ga2mTe3(m=0.98,0.96,0.92,0.75), and study the thermoelectricperformance. It was found that only the pseudobinary alloys consisting ofGa2Te3and CdTe, termed as Cd(3-3m)Ga2mTe3(m=0.98,0.96,0.92,0.75), have apotential to improve the thermoelectric performance, and the experiments alsoreveal that the compound Cd(3-3m)Ga2mTe3(m=0.98) give the highestconductivity and TE figure of merit (ZT) of0.55(682K), which is3.4times thatof intrinsic Ga2Te3.3. We have prepared the MnxGa2Te3（x=0.005,0.01,0.02,0.05,0.1,0.2,0.3）materials through doping Mn into the Ga2Te3-based compounds, and found thatthe Seebeck coefficient decreases and the electrical conductivity increases ifcompared with those of intrinsic Ga2Te3. The maximum ZT value is0.16forx=0.005at640K.4. We have observed abrupt changes in electrical conductivity and Seebeckcoefficient in the Ga2SxTe3-x（x=0.01,0.05,0.1,0.2,0.3) materials in thetemperature675K-700K and710K-750K, due to the phase transformations. However, the highest ZT value of0.17was attained at793K in the Ga2S0.3Te2.7but with duplex structure.