Ga掺杂对Cu_3SbSe_4热电性能的影响

采用熔融-淬火方法制备了Cu_(2.95)Ga_xSb_(1-x)Se_4(x=0,0.01,0.02和0.04)样品,系统地研究了Ga在Sb位掺杂对Cu_3SbSe_4热电性能的影响.研究结果表明,少量的Ga掺杂(x=0.01)可以有效提高空穴浓度,抑制本征激发,改善样品的电输运性能.掺Ga样品在625 K时功率因子达到最大值10μW/cm·K~2,比未掺Ga的Cu_(2.95)SbSe_4样品提高了约一倍.但是随着Ga掺杂浓度的进一步提高,缺陷对载流子的散射增强,同时载流子有效质量增大,导致载流子迁移率急剧下降.因此Ga含量增加反而使样品的电性能恶化.在热输运方面,Ga掺杂可以有效降低双极扩散对热导率的贡献,同时掺杂引入的点缺陷对高频声子有较强的散射作用,因此高温区的热导率明显降低.最终该体系在664 K时获得最大ZT值0.53,比未掺Ga的样品提高了近50%.

Effect of Ga doping on the thermoelectric performance of Cu3SbSe4

The Cu₃SbSe₄ compound is an environmentally friendly and low-cost medium-temperature thermoelectric material, which is featured by its low thermal conductivity. The disadvantage of this compound lies in its intrinsic poor electrical transport property. In order to improve the electrical conductivity of Cu₃SbSe₄, in this work we are to increase its carrier concentration by one to two orders of magnitude though elemental doping. The sample composition of Cu_2.95Ga_xSb_1-xSe₄ is designed to increase the hole carrier concentration by introducing Cu vacancies and substituting Ga³⁺ for Sb⁵⁺. The Cu_2.95Ga_xSb_1-xSe₄ (x=0, 0.01, 0.02 and 0.04) samples are prepared by melting-quench method. The X-ray diffraction analysis indicates that the obtained samples are of single-phase with the tetragonal famatinite structure, and the energy-dispersive X-ray spectroscopy results show that the actual compositions of the samples are very close to their nominal compositions. The effect of Ga doping on the thermoelectric performance of Cu₃SbSe₄ compound is investigated systematically by electrical and thermal transport property measurements. According to our experimental results, the hole concentration of the sample is efficiently increased by substituting Sb with a small amount of Ga (x=0.01), which can not only substantially improve the electrical conductivity but also suppress the intrinsic excitation of the sample. The maximum power factor reaches 10 μW/cm·K² at 625 K for the Ga doped sample with x=0.01, which is nearly twice as much as that of the sample free of Ga. Although the carrier concentration further increases with increasing Ga content, the hole mobility decreases dramatically with the Ga content increasing due to the increased hole effective mass and point defect scattering. Thus, the electrical transport properties of the samples deteriorate at higher Ga content, and the maximum power factors for the samples with x=0.02 and 0.04 reach 9 and 8 μW/cm·K² at 625 K, respectively. The lattice thermal conductivities of the samples basically comply with the T^-1 relationship, suggesting the phonon U-process is the dominant scattering mechanism in our samples. For the samples with x=0 and 0.01, the lattice thermal conductivities at high temperature deviate slightly from the T^-1 curve due to the presence of intrinsic excitation. However, these deviations are eliminated for the samples with x=0.02 and 0.04 because the bipolar effect is effectively suppressed with the increasing of Ga content. Thus, Ga doping can reduce the bipolar thermal conductivity at high temperature by increasing the hole carrier concentration. Furthermore, the point defects introduced by Ga doping can also enhance the scattering of high-frequency phonons, leading to slightly reduced lattice thermal conductivities of Ga-doped samples at higher temperature. Finally, a maximum ZT value of 0.53 at 664 K is achieved in Ga-doped sample, which is 50% higher than that of the sample free of Ga.