Cu掺杂AgSbTe2化合物的相稳定、晶体结构及热电性能

利用熔融快淬结合放电等离子烧结(SPS), 制备了Cu_xAg_1-xSbTe₂(x= 0---0.3)样品. 粉末X射线衍射(XRD)分析结果显示, SPS处理以前, 含Cu样品形成NaCl型结构的固溶体, 而未加入Cu的样品析出Ag₂Te第二相. 根据热分析和XRD测量结果, Cu的加入能够有效抑制Ag₂Te的析出, 但同时会在快淬样品中产生少量非晶相. 在温度升高到540 K左右时, 非晶相发生晶化, 形成Sb₇Te亚稳相, 并最终转变成Sb₂Te₃稳定相. 对快淬样品进行低温SPS快速处理后, x =0.1样品为面心立方结构的单相化合物, 但是x =0.2, 0.3的样品分别析出第二相Sb₇Te和Sb₂Te₃. 由于析出第二相, x=0.2, 0.3样品的电导率增大, Seebeck系数减小, 热导率相应升高, 综合热电性能降低. x=0.1单相样品的功率因子与文献报道的AgSbTe₂化合物相当. 元素替代的合金化效应 增强了Cu_0.1Ag_0.9SbTe₂化合物的声子散射, 有效降低了样品的热导率. 因此, 单相样品Cu_0.1Ag_0.9SbTe₂表现出较佳的热电性能, 在620 K时热电优值达到1.

Phase stability, crystal structure and thermoelectric properties of Cu doped AgSbTe2

Cu_xAg_1-xSbTe₂ samples with x = 0---0.3 are prepared by a combined process of melt-quenching and spark plasma sintering (SPS). X-ray powder diffraction (XRD) analysis indicates that single phase samples with the NaCl-type structure are obtained for the Cu-doped samples before SPS treatment, whereas a small quantity of Ag₂Te impurities coexist with the main cubic phase for the sample without Cu. According to our thermoanalysis and XRD results, the substitution of Cu for Ag can effectively prevent the precipitation of Ag₂Te, but this also leads to the presence of a minor amorphous phase in the melt-quenched sample. The amorphous phase crystallizes into Sb₇Te metastable phase at about 540 K, which finally transforms into the stable Sb₂Te₃ compound. After the SPS treatment of the melt-quenched sample, the sample with x=0.1 remains a single phase with the face-centered-cubic crystal structure, while Sb₇Te and Sb₂Te₃ are precipitated as the second phases for the samples with x = 0.2 and 0.3, respectively. The electrical conductivity increases and the Seebeck coefficient decreases with the addition of Cu due to the existence of the second phase in the samples with x = 0.2 and 0.3. Accordingly, thermal conductivities also increase with the addition of Cu, leading to the reduced thermoelectric performance of the x= 0.2 and 0.3 samples. For the sample with x = 0.1, its power factor is comparable to that of the literature reported AgSbTe₂ compound. As a result of so-called alloying effect, the phonon scattering effect is enhanced due to the partial replacement of Ag by Cu, leading to the reduced thermal conductivity of the x = 0.1 sample. Therefore, the Cu_0.1Ag_0.9SbTe₂ sample exhibits the promising thermoelectric performance and a dimensionless thermoelectric figure of merit (ZT) value of 1 is achieved at 620 K.