Mg_(3)Bi_(2)/Mg_(2)Sn纳米复合膜的微结构及热电性能

Microstructure and Thermoelectric Properties of Mg_(3)Bi_(2)/Mg_(2)Sn Nanocomposite Films

利用高真空磁控溅射技术,通过高纯Mg靶和自制Mg-Bi-Sn合金靶的顺序溅射沉积,制备了Mg_(3)Bi_(2)/Mg_(2)Sn纳米复合薄膜。沉积薄膜的晶体结构和相组成由X射线衍射(XRD)图谱确定,表面形貌和化学成分用场发射扫描电子显微镜(FESEM)和能谱仪(EDS)进行观察、测量和分析。沉积薄膜的载流子浓度和迁移率通过霍尔实验获得,电导率和Seebeck系数由Seebeck/电阻测试分析系统进行测量。结果表明,沉积薄膜由Mg_(3)Bi_(2)和Mg_(2)Sn两相组成,随着薄膜中Mg_(2)Sn含量的增加,沉积薄膜的室温载流子浓度增加而迁移率下降。在整个测试温度范围内,随薄膜中Mg_(2)Sn含量的增加,薄膜Seebeck系数不断升高而电导率下降。Mg_(2)Sn相原子含量为28.22%的沉积薄膜在155℃获得最高功率因子为1.2 mW·m^(-1)·K^(-2)。在Mg_(3)Bi_(2)薄膜中加入适量的Mg_(2)Sn第二相,可明显提升Mg_(3)Bi_(2)薄膜材料的功率因子。

Mg_(3)Bi_(2)/Mg_(2)Sn nanocomposite films were prepared by high vacuum magetron sputtering with alternately sputtering on single crystalline Si substrate containing SiO_(2)layer of 500 nm thickness using high-purity Mg target and self-made Mg-Bi-Sn alloy target.The crystal structure and phase composition of the deposited films were determined by X-ray diffraction(XRD)patterns.The morphology and surface chemical composition of the deposited films were observed,measured and analyzed by field emission scanning electron microscopy(FESEM)and energy dispersive spectrum(EDS),respectively.The carrier concentration and mobility of the deposited films were obtained by Hall experiment.The electrical conductivity and Seebeck coefficient of the deposited films were measured by Seebeck/resistance measure and analysis system.The results show that the nanocomposite film is composed of Mg_(3)Bi_(2)and Mg_(2)Sn phase.Measurement and calculation of half height width of the diffraction peak for Mg_(2)Sn phase show that the grain size of Mg_(2)Sn phase in the deposited films is 13 nm to 16 nm.With the increase of Mg_(2)Sn phase contents,the carrier concentration increases and the mobility decreases at room temperature.The phase interface is the barrier to carrier transmission,the carrier mobility decreases because of more phase interface.In the whole measured temperature range,the Seebeck coefficient increases and the conductivity decreases with the increase of Mg_(2)Sn phase contents in the deposited film.The energy filtering effect at the phase interface causes carriers with lower energy to be filtered out,and the energy of carriers in the film is more concentrated,namely,the d p(E)/d E increases,causing Seebeck coefficient increases with the increase of phase interface.The film with 28.22%Mg_(2)Sn atomic content of phase can obtain the highest power factor value of 1.2 mW·m^(-1)·K^(-2)at 155℃.The power factor of Mg_(3)Bi_(2)film can be significantly improved by adding proper amount of Mg_(2)Sn second phase into Mg_(3)Bi_(2)film,forming nanocomposite films.