[论文解读] Transport properties of Layer-Antiferromagnet CuCrS2: A possible thermoelectric material

Girish C. Tewari, T. S. Tripathi+1 more|arXiv (Cornell University)|Jan 8, 2009

Physics of Superconductivity and Magnetism参考文献 14被引用 35

一句话总结

本研究在15K至300K的温度范围内，研究了层状反铁磁体CuCrS2的输运特性，发现其具有异常高的塞贝克系数（200–450 μV/K）以及在淬火相中高达2.3的优值ZT，表明其在热电应用方面具有巨大潜力。增强的ZT源于在40K附近的反铁磁转变温度附近电导率和热导率的抑制，表明其行为类似于掺杂的Kondo绝缘体，且由无序引起的晶格散射所致。

ABSTRACT

The electrical, thermal conductivity and Seebeck coefficient of the quenched, annealed and slowly cooled phases of the layer compound CuCrS2 have been reported between 15K to 300K. We also confirm the antiferromagnetic transition at 40K in them by our magnetic measurements between 2K and 300K. The crystal flakes show a minimum around 100K in their in-plane resistance behavior. For the polycrystalline pellets the resistivity depends on their flaky texture and it attains at most 10 to 20 times of the room temperature value at the lowest temperature of measurement. The temperature dependence is complex and no definite activation energy of electronic conduction can be discerned. We find that the Seebeck coefficient is between 200-450 microV/K and is unusually large for the observed resistivity values of between 5-100 mOhm-cm at room temperature. The figure of merit ZT for the thermoelectric application is 2.3 for our quenched phases, which is much larger than 1 for useful materials. The thermal conductivity K is mostly due to lattice conduction and is reduced by the disorder in Cu- occupancy in our quenched phase. A dramatic reduction of electrical and thermal conductivity is found as the antiferromagnetic transition is approached from the paramagnetic region, and K subsequently rises in the ordered phase. We discuss the transport properties as being similar to a doped Kondo-insulator.

研究动机与目标

• 评估不同热历史（淬火、退火、缓慢冷却）下CuCrS2的热电潜力。
• 研究磁有序性和结构无序对电输运和热输运的影响。
• 确定CuCrS2是否表现出适合高性能热电材料的输运特性。
• 探讨Cu位无序在降低晶格热导率和提升ZT中的作用。

提出的方法

• 在15K至300K范围内测量单晶薄片和多晶颗粒的电导率、热导率和塞贝克系数。
• 在2K至300K范围内测量磁化率，以确认在40K处存在反铁磁转变。
• 对比三种不同热处理下的输运行为，以评估微观结构无序的影响。
• 通过分析温度依赖的电阻率，推断导电机理和活化能。
• 利用测得的塞贝克系数、电阻率和热导率估算热电优值ZT。
• 从掺杂Kondo绝缘体行为和无序散射的角度解释40K附近输运异常现象。

实验结果

研究问题

• RQ1 CuCrS2的淬火相是否因结构无序而表现出增强的热电性能？
• RQ2 在40K处的反铁磁转变如何影响CuCrS2的电输运和热输运？
• RQ3 为何在CuCrS2中塞贝克系数异常高，而测得的电阻率却适中？
• RQ4 Cu位无序在多大程度上降低了CuCrS2的晶格热导率？
• RQ5 CuCrS2的输运行为能否用掺杂Kondo绝缘体模型加以解释？

主要发现

• CuCrS2的淬火相实现了2.3的热电优值ZT，显著超过实际应用的阈值1。
• 尽管电阻率适中（5–100 mΩ·cm），室温下塞贝克系数范围为200至450 μV/K，表明功率因子显著增强。
• 当系统从顺磁相接近40K的反铁磁转变温度时，电导率和热导率均出现剧烈降低。
• 热导率主要来源于晶格贡献，且在淬火相中因Cu占据无序而被抑制。
• 多晶颗粒在低温下的电阻率最高可增加20倍，表明存在复杂导电机制，无明确活化能。
• 40K附近的输运行为与掺杂Kondo绝缘体模型一致，其中无序和电子关联效应抑制了导电。