Doping Modification Of BiCuSeO Thermoelectric Materials

p-type BiCuSeO, a layered oxychalcogenide has received more and more attentionsince its lowing thermal conductivity. However,the low instinct conductivity ofBiCuSeO limits the useage of thermoelectric materials.Studies have found that itsconductivity can be promoted through doping method, so as to improve thethermoelectric performance.In this work，Mg dropping、Na dropping and S droppingBiCuSeO composition were synthesized by a two-step solid state reaction route， thendensitified by spark plasma sintering system （SPS） The phase structure of thepowders was analyzed byXRD、SEM and the TE properties of the SPS pellets areconducted by Ulvac Riko ZEM-2、Netzsch LFA427、DSC、PPMS.Thermoelectric properties of Mg-doped Bi_1-xMg_xCuSeO （0.0≤x≤0.125） systemhas been investigated in the temperature range300–923K. Studies have shown thatdoping samples are pure phase structure.The substitution of Bi3+by Mg2+leads to anenhancement of the electrical conductivity and a decrease of the thermal conductivity.Coupled to high Seebeck coefficients, ZT at923K is increased from0.45for pristineBiCuSeO to0.67for Bi0.95Mg0.05CuSeO. However, the efficiency of Mg doping in theinsulating （Bi₂O₂）²⁺layer is low, and this doping only leads to a limited increase of thehole carriers concentration. Therefore Mg doped BiCuSeO has relatively low electricalconductivity which makes its thermoelectric figure of merit much lower than that of Ca,Sr and Ba doped BiCuSeO.(Bi_0.925Ca_0.075CuSeO⁰.90, Bi_0.875Ba_0.125CuSeO¹.1，Bi_0.925Sr_0.075CuSeO0.76)Thermoelectric properties of Na-doped Bi_1-xNa_xCuSeO （0.0≤x≤0.02） system hasbeen investigated in the temperature range300–873K. After Na dropped， the carrierconcentration showed an effective increase to1.3×10²⁰ cm^-3at the doping amount ofx=0.02, resulting in the increase in the power factor as high as8×10^-4μWcm-1K-2atroom temperature. However, the power factors of Na-doped samples decrease withincreasing temperature, opposite to the trend for alkaline earth metal doped samples. AZT of0.86is achieved at873K for Bi0.98Na0.02CuSeO sample, representing a60%enhancement with respect to an undoped sample at the same temperature.Thermoelectric properties of S-doped BiCuSeO_1-xS_x（0≤x≤0.05） system has beeninvestigated in the temperature range300–923K.After S dropped which the substitutionof oxygen by sulfur,has a significant impact on the thermoelectric transport properties.The S doped samples do not yield a certain increase in the carrier concentration, butshow a significant improvement in the carrier mobility due to the modified band angles. As a result, electrical conductivity increases at the same time seebeck coefficientremains high, which results in high power factor. Coupled with low thermalconductivity, the highest dimensionless thermoelectric figure of merit1.2is achieved at923K for BiCuSeO0.98S0.02, revealing S-substitution is an effective method ofimproving the thermoelectric performance of BiCuSeO oxside...