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Development of lanthanoid sulfides for ceramics condenser with large-capacity

大容量陶瓷电容器用镧系元素硫化物的研制

基本信息

批准号：
16360369
负责人：
HIRAI Shinji
金额：
$ 9.15万
依托单位：
Muroran Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2006
项目状态：
已结题

项目摘要

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.

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）。除了Lu之外，获得了不含中间产物如氧硫化物的合成粉末。在Eu的情况下获得单硫化物。通过优化稀土金属与硫的配比，提高了材料的热电性能。对于γ-GdS_x压块，热电优值ZT随硫含量的降低而增大，当x = 1.43时，ZT达到0.16。此外，还测试了<1.5>在合成粉末中添加Ti控制晶相的γ-LaS_2压块的热电性能。氧杂质影响从四方β相到y相的转变。β相实际上是氧硫化物La_<10>S_<14>（O_<1-x>S_x），其0 ≤ x ≤ 1。虽然氧的存在在宽的温度范围内稳定了四方晶型，但具有低氧含量的β相在约1600 K下经历进一步转变为y相。我们观察到Ti的加入促进了La_<10>S_<14>O向γ相的转变。在γ相中加入8 wt. % Ti，ZT随温度升高而增大，在1000 K时达到0.21。Ti添加剂由于促进了具有高热电性能的y相的形成而适合于改善高温热电性能。此外，含Ti的β相是高温热电转换的候选材料。塞贝克系数的大小随温度的升高而增大，而电阻率则随温度的升高而减小。因此，ZT从300 K时的0.013突然增加到1000 K时的0.18。