Lattice dynamics of thermoelectric palladium sulfide Liu-Cheng Chen a, b, c , Qing Peng d , Hao Yu c , Hong-Jie Pang c , Bin-Bin Jiang e, f , Lei Su g , Xun Shi e , Li-Dong Chen e , Xiao-Jia Chen c, * a Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China b University of Science and Technology of China, Hefei 230026, China c Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China d Department of Nuclear Engineering and Radiological Science, University of Michigan, Ann Arbor, MI, 48109, USA e State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Science, Shanghai 200050, China f University of Chinese Academy of Sciences, Beijing 100049, China g Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China article info Article history: Received 25 March 2019 Received in revised form 21 May 2019 Accepted 23 May 2019 Available online 26 May 2019 Keywords: Palladium sulfide X-ray diffraction Raman spectra Ab initio calculations abstract Highly efficient thermoelectric materials always have low thermal conductivities. Their phonon spec- trum information is essential for understanding the procedure of thermal transport on thermoelectrics. Recently, palladium sulfide was found to be a potential thermoelectric material. However, the high thermal conductivity limits its thermoelectric performance and technological applications. Here, the phonon dispersion and phonon density of state in PdS are presented by using the first-principles theory. The phonon modes are assigned and compared with experiments. The evolution of optical modes with pressure is studied by using Raman spectroscopy. The low-energy and high-energy phonon bands are related to the vibrations of the heavy atom and the light atom, respectively. By combining Raman scattering and X-ray diffraction measurements, we obtain the mode-Grüneisen parameters for the detected phonon modes. The small mode-Grüneisen parameters indicate a weak anharmonicity in this material. This offers an explanation for its high thermal conductivity. The evolution of linewidths with pressure accounts for the decrease of the thermal conductivity upon compression. © 2019 Elsevier B.V. All rights reserved. 1. Introduction Currently, the world is facing numerous challenges relating to energy supply and environment consumption. High-efficiency thermoelectric materials, which can directly convert waste heat into electric power without producing unusable heat, process great potential to settle these conditions. The dimensionless figure of merit (zT ), which can be expressed as zT ¼ S 2 T sk 1 , where S is the Seebeck coefficient, s is the electrical conductivity, T is the absolute temperature, and k is the thermal conductivity, determines the maximum efficiency of the conversion process. This formula ex- presses the fact that large S, high s, and low k will be need for a high efficiency [1e3]. In fact, the produced electrical energy is in the form of current which is driven by thermoelectric voltage. Mean- while, considering the parasitic relationship between heat conduction and electrical resistance, it is obvious that efficient thermoelectric materials always have low thermal conductivities [4e6]. Palladium sulfide (PdS), which belongs to transition metal sulfides with an ideal band gap of 1.6eV, has many potential ap- plications in semiconducting, photoelectrochemical and photovol- taic fields [7e9]. In addition, it also presented many potential device applications in catalysis and acid resistant and high tem- perature electrodes [10, 11]. Surprisingly, PdS also presents super- conducting properties under pressure [12]. As a potential thermoelectric, it possesses intrinsic large power factors of 27 mWcm 1 K 2 and a moderate zT value around 800 K. The relative high thermal conductivity (24 Wm 1 K 1 ) is the main factor for limiting its thermoelectric performance [13, 14]. Thus, if the large thermal conductivity could be suppressed while keeping the good electrical properties, PdS will be a good candidate for thermo- electric applications. Due to the crucial role of phonon information for understanding the thermal transport properties in thermoelectric materials, it is necessary to analysis the phonon dispersion and other related * Corresponding author. E-mail address: xjchen@hpstar.ac.cn (X.-J. Chen). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom https://doi.org/10.1016/j.jallcom.2019.05.280 0925-8388/© 2019 Elsevier B.V. All rights reserved. Journal of Alloys and Compounds 798 (2019) 484e492