锂受主掺杂调控Ca₂Si的电学性能及热学性能

Tuning Electrical and Thermal Properties of Ca₂Si by Li Acceptor Doping

摘要: 通过将原材料封装在钽管中熔炼和高真空热压合成了Li_xCa_(2-x)Si (x = 0, 0.02, 0.04, 0.06, 0.08)半导体热电材料。利用X射线衍射(XRD)、扫描电子显微镜(SEM)分别对样品的物相结构和断面形貌进行了表征。XRD结果表明：Li_xCa_(2-x)Si块体材料的XRD图谱与Ca₂Si的XRD图谱对应一致，但所有样品中都出现Ca₅Si₃

Abstract: 衍射峰。SEM结果表明：Li_xCa_(2-x)Si块体材料的组织较致密，颗粒大小均匀，平均颗粒大约2~3 μm。在300~873 K温度范围内研究了Li掺杂对Ca₂Si电导率和泽贝克系数的影响，随着Li掺杂浓度的增加，电导率逐渐增大，泽贝克系数则逐渐减小。在300~873 K温度范围内，较高浓度掺杂的Li_xCa_(2-x)Si (x = 0.04, 0.06, 0.08)样品的功率因子均下降。在650 K到873 K的温度范围内，Li掺杂浓度为x = 0.02的功率因子得到了提高。Li掺杂后热导率均高于Ca₂Si的热导率，并且随着Li掺杂浓度的增加，热导率出现规律性升高的现象。Li掺杂浓度为x = 0.02时，在650 K到873 K的温度范围内，Li掺杂优化了Ca₂Si的热电优值，在873 K的最大热电无量纲优值为0.20。 Li_xCa_(2-x)Si (x = 0, 0.02, 0.04, 0.06, 0.08) thermoelectric materials were fabricated by melting in tantalum tube and high vacuum hot pressing. Phase structures and cross-section morphology of the samples were analyzed by means of x-ray diffraction (XRD) and scanning electronic microscopy (SEM), respectively. The XRD results show that the characteristic peaks of the bulk Li_xCa_(2-x)Si can be indexed into Ca₂Si. The peak of Ca₅Si₃ exists in the XRD patterns of the all bulk samples. The SEM results show that microstructure of the bulk Ca_(2-x)Si (x = 0, 0.02) is dense. Uniform particle size is about 2 - 3 μm. The electrical conductivity and Seebeck coefficient of Li_xCa_(2-x)Si (x = 0, 0.02，0.04, 0.06, 0.08) were studied in the temperature range of 300 - 873 K. The electrical conductivity of the Li-doped samples increases with increasing Li concentration, on the contrary, the Seebeck coefficient of the Li-doped samples decreases. The power factors of higher concentration Li-doped Ca2Si decrease in the temperature range of 300 - 873 K. The power factors of Li_xCa_(2-x)Si (x = 0.02) are improved in the temperature range of 650 - 873 K. The thermal conductivity of the Li_xCa_(2-x)Si (x = 0.02, 0.04, 0.06, 0.08) samples was investigated in the temperature range of 300 - 873 K. Compared with the Ca₂Si sample, the thermal conductivity of the Li-doped samples regularly in-creases with increasing Li concentration. The zT values of Li_xCa_(2-x)Si with x = 0.02 sample have an enhancement in the temperature range of 650 - 873 K by contrast with those of the Ca₂Si sample. The maximum zT value was 0.20 at 873 k.