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arXiv 1204.3231cond-mat.mtrl-sci
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Ca3Co4O9的结构相变与高温热电性能的增强

A Structural Phase Transition in Ca3Co4O9 Associated with Enhanced High Temperature Thermoelectric Properties

Tao Wu, Trevor A. Tyson, Haiyan Chen, Jianming Bai, Hsin Wang, Cherno Jaye

摘要:

随温度变化的电阻率,晶体结构和热容的测量揭示了电阻率下降和金属到半导体的转变对应于一阶结构相变在400 K附近的Ca 3Co 4 O 9。晶格参数c随温度的升高而平稳变化,而a、b1和b2晶格参数在~ 400 K时出现异常。Ca_2CoO_3和CoO_2层在~ 400 K以上发生变形,这与金属到半导体的输运行为变化有关。在磁场下测量电阻率和热容随温度的变化表明,自旋对这种转变的贡献很小。与从金属到半导体行为的第一级相变相关的降低的电阻率增强了高温下的热电性能,并指出金属到半导体的转变是高温热电氧化物中改善ZT的机制。

英文摘要:

Temperature dependent electrical resistivity, crystal structure and heat capacity measurements reveal a resistivity drop and metal to semiconductor transition corresponding to first order structural phase transition near 400 K in Ca3Co4O9. The lattice parameter c varies smoothly with increasing temperature, while anomalies in the a, b1 and b2 lattice parameters occur at ~ 400 K. Both Ca2CoO3 and CoO2 layers become distorted above ~ 400 K associated with the metal to semiconductor transport behavior change. Resistivity and heat capacity measurements as a function of temperature under magnetic field indicates low spin contribution to this transition. Reduced resistivity associated with this first order phase transition from metallic to semiconducting behavior enhances the thermoelectric properties at high temperatures and points to the metal to semiconductor transition as a mechanism for improved ZT in high temperature thermoelectric oxides.

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