Cu2Se相变过程中热电效率增强的电子起源

Electronic origin of the enhanced thermoelectric efficiency of CuSe

热电材料可实现热能向电能的转换,是解决能源危机的潜在方式.目前热电材料的发展受限于较低的热电转换效率(可由热电优值zT评估),探索新型高zT热电材料或提升现有热电材料的z T值是亟待解决的重要课题.Cu2Se作为一种传统的超离子高z T热电材料一直备受关注.研究表明在其400 K附近的相变过程中,z T迅速提升了3倍.目前对这一变化的研究多限于晶体结构方面,而电子性质研究仅限于理论计算.本文利用高分辨角分辨光电子能谱技术,详细测量了相变过程其能带结构随温度的演变,揭示了相变过程中Cu2Se的电子结构的剧烈重组.作者利用光电子强度近似的模拟Cu2Se费米能级附近的电子态随温度的演化,并采用Mott模型来估算在相变过程中Seebeck系数的演化,再现了输运实验中Seebeck系数的提升.本研究表明电子结构在体系的热电性质中起了非常重要的作用,为理解和优化材料的热电性能提供了一种可能的方法.

Thermoelectric materials(TMs)can uniquely convert waste heat into electricity,which provides a potential solution for the global energy crisis that is increasingly severe.Bulk Cu2Se,with ionic conductivity of Cu ions,exhibits a significant enhancement of its thermoelectric figure of merit z T by a factor of^3 near its structural transition around 400 K.Here,we show a systematic study of the electronic structure of Cu2Se and its temperature evolution using high-resolution angle-resolved photoemission spectroscopy.Upon heating across the structural transition,the electronic states near the corner of the Brillouin zone gradually disappear,while the bands near the centre of Brillouin zone shift abruptly towards high binding energies and develop an energy gap.Interestingly,the observed band reconstruction well reproduces the temperature evolution of the Seebeck coefficient of Cu2 Se,providing an electronic origin for the drastic enhancement of the thermoelectric performance near 400 K.The current results not only bridge among structural phase transition,electronic structures and thermoelectric properties in a condensed matter system,but also provide valuable insights into the search and design of new generation of thermoelectric materials.