The thermoelectric properties of a series of the polycrystalline samples of titanium dichalcogenides with partial substitution of Ti for Nb and S for Se were investigated. It was found that sintering of the samples improved the thermoelectric efficiency (ZT), and the maximum ZT was achieved at sintering temperature of 600°C. A further increase in the sintering temperature (850°C and 950°C) led to the recrystallization of the samples, as a result, the Seebeck coefficient sharply decreased and electrical conductivity dramatically increased. The temperature dependences of electrical conductivity σ(T) in the temperature range from 4.2 to 300 K and Seebeck coefficient S(T) in the temperature range from 77 to 300 K were investigated in order to determine the nature of the observed improvements in thermoelectric properties due to double substitutions and sintering. Two‐dimensionalization of electron transport properties of Ti_1−xNb_xS_2−ySe_y solid solutions was found. The Fermi energy E_F2D was estimated using the temperature dependences of Seebeck coefficient. The relationship between the Fermi energy E_F2D and figure of merit ZT was established. The effect of sintering on parameters σ(T), S(T), charge carrier concentration (n_2D), mobility (µ), and thermal conductivity (k) was found. The optimal value of Fermi energy E_F2D in terms of figure of merit ZT = 0.31 at room temperature (T = 300 K) was found for Ti_0.98Nb_0.02S_1.3Se_0.7 sample sintered at 600°C.

中文翻译：

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层状Ti1-xNbxS2-ySey固溶体的改进的热电性能

研究了一系列钛二卤化物多晶样品的热电性能，其中钛部分替代了Nb，S部分替代了Se。发现样品的烧结提高了热电效率（ZT），并且在600℃的烧结温度下实现了最大ZT。烧结温度（850℃和950℃）的进一步升高导致样品的重结晶，结果，塞贝克系数急剧下降，电导率急剧增加。电导率σ（T）在4.2至300 K的温度范围内的温度依赖性和塞贝克系数S（T为了确定所观察到的由于双取代和烧结引起的热电性能改善的性质，对温度为77-300K的温度进行了研究。发现Ti _{1- x} Nb _x S _{2- y} Se _y固溶体的电子输运性质为二维。费米能量E _F2D使用塞贝克系数的温度依赖性进行估算。建立了费米能量E _{F 2 D}与品质因数ZT的关系。烧结对参数σ（T）的影响求出S（T），载流子浓度（n _2D），迁移率（μ）和热导率（k）。对于在600°C烧结的 Ti _0.98 Nb _0.02 S _1.3 Se _0.7样品，发现 在室温（T = 300 K）下，基于品质因数ZT = 0.31的费米能E _F2D的最佳值。