Development of lanthanoid sulfides for ceramics condenser with large-capacity

用稀土氧化物与CS_2气体反应合成了稀土倍半硫化物R_2S_3(R：La，Ce，Pr，Nd，Sm，Eu，Gd，Tb，Dy，Ho，Yb，Lu)。除Lu外，合成粉末不含中间产物，如硫氧化物。在Eu的情况下，得到了一种单硫化物。通过优化稀土金属与硫的比例，改善了材料的热电性能。对于γ-GDS_x系压敏材料，热电优值系数ZT随硫含量的降低而增大，在x=1.43时达到0.16.此外，还测量了γ-LAS_&lt；1.5&gt；压坯的热电性能，其晶相是通过在合成粉末中添加钛来控制的。氧杂质对四方β相向y相的转变有影响。β相实际上是一个氧硫化物La_&lt；10&gt；S_&lt；14&gt；(O_&lt；1-x&gt；S_x)，0[小于等于]x[小于等于]1.氧的存在在较宽的温度范围内稳定了四方相，而低氧含量的β相在1600K左右进一步向y相转变。我们观察到钛的加入促进了La&lt；10&gt；S&lt；14&gt；O向γ相的转变。在含8wt.%Ti的γ相中，ZT随温度升高而增大，在1000K时达到0.21.钛的添加促进了具有较高热电性能的y相的形成，适合于改善高温热电性能.此外，含钛的β相也是高温热电转换的候选材料。塞贝克系数随温度升高而增大，而电阻率随温度升高而减小。因此，ZT从300K时的0.013突然增加到1000K时的0.18.

Rare-earth sesquisulfides R_2S_3 (R : La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, and Lu) were synthesized by the reaction of rare-earth oxides with CS_2 gas. With the exception of Lu, synthetic powders devoid of intermediate products such as an oxysulfide were obtained. A monosulfide was obtained in the case of Eu. The thermoelectric properties were improved by the optimization of the ratios of rare-earth metal to sulfur. For a γ-GdS_x compact, the thermoelectric figure of merit ZT increased with a decrease in the sulfur content and reached a value of 0.16 at x = 1.43. Moreover, the thermoelectric properties were measured for the γ-LaS_<1.5> compact whose crystal phase was controlled by the addition of Ti to a synthetic powder. The transformation from the tetragonal β-phase to the y-phase is affected by the oxygen impurities. The β-phase is in fact an oxysulfide La_<10>S_<14>(O_<1-x>S_x) with 0【less than or equal】x【less than or equal】1. While the presence of oxygen stabilizes the tetragonal form over a wide temperature range, the β-phase with a low oxygen content undergoes further transformation to the y-phase at around 1600 K. We observe that the Ti additive promotes the transformation from La_<10>S_<14>O to the γ-phase. In the γ-phase with 8 wt. % Ti, ZT increases with the temperature and reaches a value of 0.21 at 1000 K. The Ti additive is suitable for improving the high-temperature thermoelectric properties because it promotes the formation of the y-phase with high thermoelectric performance. Moreover, the β-phase with Ti is a candidate material for high-temperature thermoelectric conversion. The magnitude of the Seebeck coefficient increases with the temperature, while the electrical resistivity decreases. Consequently, ZT increases abruptly from 0.013 at 300 K to 0.18 at 1000 K.