New Chemistry Unit and Theoretical Science Unit, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Jakkur P.O., Bangalore, India.
Variable Energy Cyclotron Centre, 1/AF Bidhannagar, Kolkata, 700064, India.
Angew Chem Int Ed Engl. 2018 Apr 3;57(15):4043-4047. doi: 10.1002/anie.201801491. Epub 2018 Mar 12.
Crystalline solids with intrinsically low lattice thermal conductivity (κ ) are crucial to realizing high-performance thermoelectric (TE) materials. Herein, we show an ultralow κ of 0.35 Wm K in AgCuTe, which has a remarkable TE figure-of-merit, zT of 1.6 at 670 K when alloyed with 10 mol % Se. First-principles DFT calculation reveals several soft phonon modes in its room-temperature hexagonal phase, which are also evident from low-temperature heat-capacity measurement. These phonon modes, dominated by Ag vibrations, soften further with temperature giving a dynamic cation disorder and driving the superionic transition. Intrinsic factors cause an ultralow κ in the room-temperature hexagonal phase, while the dynamic disorder of Ag/Cu cations leads to reduced phonon frequencies and mean free paths in the high-temperature rocksalt phase. Despite the cation disorder at elevated temperatures, the crystalline conduits of the rigid anion sublattice give a high power factor.
具有固有低热导晶格的晶态固体对于实现高性能热电（TE）材料至关重要。本文报道了 AgCuTe 的超低热导率 κ 值为 0.35 Wm K ，当与 10 mol% Se 合金化时，其在 670 K 时的热电优值 zT 达到 1.6。第一性原理 DFT 计算揭示了其室温六方相中的几种软声子模式，低温热容测量也证实了这一点。这些主要由 Ag 振动引起的声子模式随着温度的升高而进一步软化，导致动态阳离子无序，并驱动超离子转变。本征因素导致室温六方相具有超低的 κ 值，而 Ag/Cu 阳离子的动态无序导致高温岩盐相中声子频率和平均自由程降低。尽管在高温下存在阳离子无序，但刚性阴离子亚晶格的晶体通道提供了高功率因子。
