Thermopower studies of a series of salts of tetramethyltetrathiafulvalene [(TMTTF) 2 X, X=Br, ClO 4 , NO 3 , SCN, BF 4 , AsF 6 , and PF 6 ]
Thermopower studies of a series of salts of tetramethyltetrathiafulvalene [(TMTTF) 2 X, X=Br, ClO 4 , NO 3 , SCN, BF 4 , AsF 6 , and PF 6 ]
复制标题
四甲基四硫富瓦烯系列盐的热电研究 [(TMTTF) 2 X, X=Br, ClO 4 , NO 3 , SCN, BF 4 , AsF 6 , and PF 6 ]
DOI：
10.1103/physrevb.28.5856
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发表时间：
1983
影响因子：
3.7
通讯作者：
J. Fabre
中科院分区：
文献类型：
--
作者：
K. Mortensen;E. Conwell;J. Fabre
对一组四甲基四硫富瓦烯 (TMTTF) 2 X 盐的热电势测量显示出多种行为。在温度 300≥ T≳ 100 K 范围内，几种盐 (X= B F 4, Cl O 4, N O 3, SCN) 具有恒定热电势 S≃ 35 μV/K，而 P F 6 和 As F 6 盐具有 S∝ 1 T，Br 盐的 S 随 T 增加。低于～ 100 K，每种盐的 S 随温度降低而急剧增加或减少除 SCN 盐外，其与相变无关。这些材料已被确定为低于电导率 σ vs T 最大值的半导体。我们给出的论点是，费米能隙在高于最大值的温度下也存在。间隙的存在很好地证明了该材料的特征在于第二个电子在大于带宽 4 t 的位置上具有库仑斥力 U。然而，对于 100 K 以上的几种化合物发现的常数有限 S< 60 μV/K 表明 U 并不比 4 t 大很多。 P F 6 和As F 6 盐在相同温度范围内S的不同行为以及低温下S与T的急剧变化（SCN盐除外）归因于缺陷而不是例如局域化。在 SCN、Cl O 4 和 Br 盐中，在低温下观察到的特征反映了这些材料中已知的相变。
Thermoelectric power measurements on a group of tetramethyltetrathiafulvalene (TMTTF) 2 X salts show a wide variety of behavior. In the range of temperatures 300≥ T≳ 100 K several of the salts (X= B F 4, Cl O 4, N O 3, SCN) have a constant thermopower S≃ 35 μV/K, while the P F 6 and As F 6 salts have S∝ 1 T, and the Br salt has S increasing with T. Below∼ 100 K, S shows a steep increase or decrease with decreasing temperature for each salt which, with the exception of the SCN salt, is not associated with a phase transition. These materials had been identified as semiconductors below the maximum in conductivity σ vs T. We give arguments that the gap at the Fermi energy exists at temperatures above the maximum as well. The existence of a gap is good evidence that the material is characterized by Coulomb repulsion U for a second electron on a site larger than the bandwidth 4 t. However, the constant finite S< 60 μV/K found for several of the compounds above∼ 100 K suggests that U is not much larger than 4 t. The different behavior of S for the P F 6 and As F 6 salts in the same temperature range and the sharp changes in S vs T at low temperatures (except for the SCN salt) are attributed to defects rather than, eg, localization. In the SCN, Cl O 4, and Br salts, features are seen at low temperatures that reflect known phase transitions in these materials.