β‐CsCu₅Se₃: A Promising Thermoelectric Material going beyond Photovoltaic Application

Abstract

Copper chalcogenides have attracted much attention in recent years because of their promising applications in thermoelectric conversion. However, many of them suffer from phase transformation at low temperature. Motivated by the synthesis of bulk β‐CsCu5Se3 with high phase transformation temperature of 923 K for photovoltaic applications, its thermoelectric properties using first‐principles calculations combined with Boltzmann transport theory are systematically studied. The results show that β‐CsCu5Se3 possesses ultralow lattice thermal conductivities of 0.24, 0.41, and 0.25 W mK−1 along the x, y, and z directions at room temperature, respectively, which are further reduced to 0.09, 0.15, and 0.09 W mK−1 at 800 K. A detailed analysis of its group velocity, three phonon scattering rate, Grüneisen parameter and three phonon phase space reveals that the weak harmonicity and strong phonon anharmonic scattering are responsible for the ultralow lattice thermal conductivity, leading to a high figure of merit (ZT) value of 1.81 along the y direction at 800 K, which is three times higher than that of known thermoelectric materials o‐CsCu5S3 (0.46 at 800 K) and t‐CsCu5S3 (0.56 at 875 K). This study suggests that β‐CsCu5Se3 is a multifunctional material promising for both photovoltaic and thermoelectric applications.

Anisotropic Electron and Phonon Transport Properties in Pnictogen Chalcohalides: PnSI (Pn = Sb, Bi)

“…In addition, Debye temperature defined as the crystal’s maximum vibration temperature for the corresponding mode is calculated using the relation, θ D = h υ m / k B , ( h is Planck constant, v m is the maximum frequency of the particular phonon mode, and k B is the Boltzmann constant) . The calculated θ D for TA, TA’, and LA modes are 72, 73, and 59 and 59, 59, and 62 K for SbSI and BiSI, respectively.…”

One-dimensional van der Waals BiSBr: an anisotropic thermoelectric mineral

“…Here, y D was calculated using the relation y D = hv m /k B , where h is Planck's constant, v m is the highest frequency of the mode, and k B is Boltzmann's constant. 61 The y D values calculated for the TA, TA 0 , and LA modes were 57, 61, and 64 K, respectively. The average Debye temperature…”

Functional Alkali Metal-Based Ternary Chalcogenides: Design, Properties, and Opportunities

“…Crystal structures and phases of ABZ materials with basic functional properties. ,− An asterisk (*) denotes the theoretically calculated values.…”

“…In Na 3 SbS 4 the high ionic conductivity can be attributed to the Na-ion diffusion pathways in the crystal framework, which act as 3D tunnels for ions and are formed by the two different types of sodium–sulfur polyhedra. , Similar to the example above, targeted functionalities can be induced by tuning the metal to chalcogen ratios in the material design for various alkali metal-based chalcogenide systems. CsCu 4 Se 3 is limited to a ZT of 0.06 due to a low Seebeck coefficient, unlike CsCu 5 Se 3 with a ZT of 1.81; the change in composition gives a huge increase in terms of thermoelectric properties. , However, one must consider that many of these phases of different material compositions would be metastable in nature, and intelligent synthetic routes with detailed understanding of the underlying chemistry will be needed for materializing such compositions.…”