Pressure induced convergence of conduction bands in Al doped Mg_(2)Si: Experiment and theory

High-pressure and high-temperature(HPHT)synthesis provides an effective way to tune the band structure of materials and improve their electronic properties.To investigate the influence of synthesis pressure on electronic properties,Mg_(1.97)Al_(0.03)Si samples were synthesized using the HPHT method.The maximum effective mass 0.92me is obtained for the sample prepared with the synthesis pressure of 3 GPa,leading to the biggest Seebeck coefficient
201.3 mV/K at room temperature.Meanwhile,the 3 GPa sample obtains the higher electron carrier concentration and electrical conductivity,resulting in nearly overall enhancement of power factor.The Density Functional Theory(DFT)calculations evidences that the Conduction Bands Minimum(CBM)can be tuned effectively by applied pressure and the convergence of the CBM leads to a larger effective mass of DOS,which are beneficial to the enhancement of power factors.These results indicate that high-pressure is a powerful tool to tune Mg_(1.97)Al_(0.03)Si band structures.

Realizing n-type CdSb with promising thermoelectric performance

Realizing high performance in both n-type and p-type materials is essential for designing efficient ther-moelectric devices.However,the doping bottleneck is often encountered,i.e.,only one type of conduction can be realized.As one example,p-type CdSb with high thermoelectric performance has been discovered for several decades,while its n-type counterpart has rarely been reported.In this work,the calculated band structure of CdSb demonstrates that the valley degeneracy is as large as ten for the conduction band,and it is only two for the valence band.Therefore,the n-type CdSb can potentially realize an ex-ceptional thermoelectric performance.Experimentally,the n-type conduction has been successfully real-ized by tuning the stoichiometry of CdSb.By further doping indium at the Cd site,an improved room-temperature electron concentration has been achieved.Band modeling predicts an optimal electron con-centration of∼2.0×1019 cm−3,which is higher than the current experimental values.Therefore,future optimization of the n-type CdSb should mainly focus on identifying practical approaches to optimize the electron concentration.

三维晶体中的演生粒子百科

在过去10年中,探索凝聚态系统中的演生粒子一直引起人们强烈的研究兴趣.演生粒子是出现在晶体能带简并附近的低能激发模式.自其提出以来,就一直受到人们的广泛关注,并在真实晶体材料和人工设计系统中被广泛报道.然而,至今学界一直还没有得到晶体体系中,所有可能实现的演生粒子的完整图像.本文通过系统的对称性和模型分析,首次完成了三维晶体中所有可能演生粒子的完整列表.该列表不仅包括了固体中电子体系的自旋粒子,也包括声子和人工虚拟晶体等体系中的无自旋粒子.此外,该工作也给出了演生粒子、对称性条件、有效模型和拓扑特征之间的详细对应关系.演生粒子百科的建立结束了在晶体体系中对新的演生粒子的搜寻研究,并为在物理系统中实现相关演生粒子提供了极其具体的指导.