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Raman Spectroscopy Study of Phonon Liquid Electron Crystal in Copper Deficient Superionic Thermoelectric Cu2–xTe
ACS Applied Energy Materials ( IF 5.4 ) Pub Date : 2020-01-27 00:00:00 , DOI: 10.1021/acsaem.9b02317
Juhi Pandey 1 , Shriparna Mukherjee 2 , Divya Rawat 1 , Shoeb Athar 1 , Kewal Singh Rana 1 , Ramesh Chandra Mallik 3 , Ajay Soni 1
Affiliation  

Superionic Cu2-xTe (CT) is an interesting and emerging p-type thermoelectric (TE) material due to the existence of various polymorphic phases and crystal structures, which undergo several structural phase transitions. On the basis of the stoichiometry of the CT compounds, the structure parameters, the carrier concentration (np), and the thermal conductivity (κ) can be modulated for optimum TE performance. Further, the understanding of the fundamental properties and their impact on TE parameters is not well understood because of their complex structures. We have investigated the vibrational properties of CT compounds such as Cu1.25Te (CT1.25), Cu1.6Te (CT1.6), and Cu2Te (CT2) using temperature dependent Raman studies in the temperature range of 300–773 K. Several structural phases are probed through remarkably distinct spectra for the CT compounds. The temperature transitions are complex such as (i) eutectic melting into CuTe and Te for both CT1.6 (above ∼593 K) and CT1.25 (above ∼613 K) and (ii) the structural transition from trigonal to orthorhombic and cubic phase for CT2 (above ∼553 K), which are strongly manifested in the Raman study. Further, the role of np in the Raman spectra has also been investigated. The intensity of the Raman modes (>100 cm–1) showed strong np dependence due to strong plasmon–phonon coupling. The analysis of full width at half-maximum (fwhm) of Raman peaks and qualitative estimation of phonon lifetime (τi) showed that CT2 has the minimum lattice thermal conductivity.

中文翻译:

铜不足的超离子热电Cu 2– x Te中声子液晶的拉曼光谱研究

超离子Cu 2-x Te(CT)是一种有趣且新兴的p型热电(TE)材料,由于存在多种多晶型相和晶体结构,它们经历了几个结构相变。根据CT化合物的化学计量,可以调节结构参数,载流子浓度(n p)和热导率(κ),以获得最佳的TE性能。此外,由于它们的复杂结构,对基本性质及其对TE参数的影响的理解还不太清楚。我们研究了CT化合物的振动特性,例如Cu 1.25 Te(CT1.25),Cu 1.6 Te(CT1.6)和Cu 2Te(CT2)在300–773 K的温度范围内使用依赖于温度的拉曼研究。温度过渡非常复杂,例如(i)CT1.6(约593 K以上)和CT1.25(约613 K以上)的共晶熔化成CuTe和Te,(ii)从三角形到正交晶和立方的结构过渡CT2的相位(约553 K以上)在拉曼研究中有很强的表现。此外,还研究了n p在拉曼光谱中的作用。拉曼模式的强度(> 100 cm –1)显示出很强的n p由于强烈的等离振子-声子耦合而产生的依赖性。全宽度的拉曼峰和声子寿命的定性估计的半最大值(FWHM)的分析(τ表明,CT2具有最小晶格热导率)。
更新日期:2020-01-27
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