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TlInSe_2 with a nano-modulated structure as a thermoelectric material with a high efficiency _

具有纳米调制结构的TlInSe_2作为高效率热电材料_

基本信息

批准号：
17560290
负责人：
WAKITA Kazuki
金额：
$ 2.05万
依托单位：
Osaka Prefecture University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2006
项目状态：
已结题

项目摘要

It is found that some TlInSe_2 samples indicate ferroelectricity. We observed memory effects of current-voltage characteristics. The phenomena are supposed to be the memory effects in an incommensurate phase which is often observed on other thallic compounds.Next, Photoluminescence (PL) and PL excitation spectra of TlInSe_2 crystals have been investigated. The observed board PL spectra are overlapped by two peaks centered at 1.05 and 0.95 eV. Both separated peaks are considered to be attributed to free-to-bound transition according to excitation intensity dependence of PL spectra. An activation energy of these peaks have also been estimated to evaluate donor or acceptor level associated with the emissions. Furthermore, we have observed PL excitation spectra with exciton-like peaks at 1.17 and 1.23 eV.The optical absorption of TlInSe_2 has been examined and the structure changes of the spectra were observed in the range of temperature between 60 and 150℃. From the spectra, the compound is found to has an indirect band gap and to change phonon energy associated with the transition in the temperature range. The decrease of phonon energy is attributed to the folding energy band due to a superlattice in the commensurate phase.Furthermore, TlInSe_2 crystals have been investigated by mean of angle-resolved photoemission spectroscopy. The obtained energy bands favorably agree with the calculated band structure and show quite noticeable dispersion in the direction normal to chains. A rigid shift toward lower binding energies, splitting and the formation of the mini-gap-like structures are clearly observed in the experimental electric bands with the temperature, and causing the record-breaking values of Seebeck coefficient.

发现一些TlInSe_2样品表现出铁电性。我们观察了电流-电压特性的记忆效应。这种现象被认为是不通约相中的记忆效应，这种现象在其他黄酮类化合物中经常观察到。接下来，研究了TlInSe_2晶体的光致发光(PL)和PL激发光谱。观察到的板 PL 光谱由以 1.05 和 0.95 eV 为中心的两个峰重叠。根据 PL 光谱的激发强度依赖性，两个分离的峰被认为归因于自由到结合的跃迁。还估计了这些峰的活化能，以评估与发射相关的供体或受体水平。此外，我们还观察到了在1.17和1.23 eV处有类激子峰的PL激发光谱。考察了TlInSe_2的光吸收，并观察了在60~150℃温度范围内光谱的结构变化。从光谱中，发现该化合物具有间接带隙并改变与温度范围内的转变相关的声子能量。声子能量的降低归因于相应相中超晶格导致的能带折叠。此外，利用角分辨光电子能谱研究了TlInSe_2晶体。获得的能带与计算的能带结构非常一致，并且在垂直于链的方向上显示出相当明显的色散。在实验电带中可以清楚地观察到随着温度的变化，向较低结合能的刚性转变、分裂和迷你带隙结构的形成，并导致塞贝克系数的破纪录值。