A$_2$AgIrCl$_6$（A = Cs, Rb）的预测高n型zT值与超低晶格热导率
Predicted High $n$-Type $zT$ and Ultralow Lattice Thermal Conductivity in A$_2$AgIrCl$_6$ (A = Cs, Rb)
AI总结：
本研究通过第一性原理计算，预测A$_2$AgIrCl$_6$（A=Cs、Rb）为具有超低晶格热导率的热电材料，800 K时n型zT峰值达2.81，具备优异热电性能。
AI中文摘要：
实用的热电器件必须阻碍热流同时不阻碍电荷输运。本研究通过第一性原理计算，从结构稳定性、化学键合、弹性响应、晶格动力学以及散射分辨载流子输运等方面，探究立方相Cs$_2$AgIrCl$_6$和Rb$_2$AgIrCl$_6$在上述平衡中的表现。两种材料均满足立方弹性稳定性判据，且谐和声子谱均无虚频。用Rb取代Cs主要产生化学压力：晶格收缩1.34%，Ag-Cl与Ir-Cl键增强，而带边拓扑变化很小。包含自旋-轨道耦合的HSE06计算给出Cs$_2$AgIrCl$_6$和Rb$_2$AgIrCl$_6$的X点直接带隙分别为1.597 eV和1.637 eV。三个对称等价的X谷具有0.43-0.57 $m_0$的轻电子质量，空穴质量则在2.10-4.68 $m_0$范围内。对于Cs$_2$AgIrCl$_6$和Rb$_2$AgIrCl$_6$，修正的Debye-Callaway模型给出300 K时的晶格热导率分别为0.346 W·m⁻¹·K⁻¹和0.428 W·m⁻¹·K⁻¹，800 K时降至0.118 W·m⁻¹·K⁻¹和0.150 W·m⁻¹·K⁻¹。采用AMSET处理声学形变势、电离杂质与极性光学声子散射，得到800 K、掺杂浓度约6×10¹⁹ cm⁻³时，n型zT峰值分别为2.81和2.36。该性能源于轻的谷简并电子、中等掺杂及弱晶格热输运的协同作用，而非单一优异系数。预测值为可实验验证的目标，前提是在高温下保持立方相并实现可控电子掺杂。
英文摘要：
A useful thermoelectric device must impede heat flow without impeding charge transport. Here, we examine how closely cubic Cs$_2$AgIrCl$_6$ and Rb$_2$AgIrCl$_6$ approach this balance using first-principles calculations of structural stability, chemical bonding, elastic response, lattice dynamics, and scattering-resolved carrier transport. Both materials satisfy the cubic elastic-stability criteria, and neither harmonic phonon spectrum contains an imaginary mode. Replacing Cs with Rb mainly exerts chemical pressure: the lattice contracts by 1.34\% and the Ag--Cl and Ir--Cl bonds strengthen, whereas the band-edge topology changes little. HSE06 calculations including spin--orbit coupling yield direct X-point gaps of 1.597 and $1.637\,\mathrm{eV}$ for Cs$_2$AgIrCl$_6$ and Rb$_2$AgIrCl$_6$, respectively. The three symmetry-equivalent X valleys have light electron masses of $0.43$--$0.57\,m_0$, whereas the hole masses span $2.10$--$4.68\,m_0$. For Cs$_2$AgIrCl$_6$ and Rb$_2$AgIrCl$_6$, respectively, the modified Debye--Callaway model gives lattice thermal conductivities of 0.346 and $0.428\,\mathrm{W\,m^{-1}\,K^{-1}}$ at 300 K, decreasing to 0.118 and $0.150\,\mathrm{W\,m^{-1}\,K^{-1}}$ at 800 K. Treating acoustic-deformation-potential, ionized-impurity, and polar-optical-phonon scattering with AMSET gives peak $n$-type $zT$ values of 2.81 and 2.36 at 800 K near $6\times10^{19}\,\mathrm{cm^{-3}}$. This response arises from the convergence of light, valley-degenerate electrons, intermediate doping, and weak lattice heat transport rather than from a single exceptional coefficient. The predicted values are experimentally testable targets, contingent on retaining the cubic phases and controlled electron doping at elevated temperatures.
