Vol.:(0123456789) 1 3 Applied Physics A (2018) 124:98 https://doi.org/10.1007/s00339-017-1540-y Thermoelectric properties of p-type sb-doped Cu 2 SnSe 3 near room and mid temperature applications K. Shyam Prasad 1  · Ashok Rao 1  · Nagendra S. Chauhan 2  · Ruchi Bhardwaj 2  · Avinash Vishwakarma 2  · Kriti Tyagi 2 Received: 23 November 2017 / Accepted: 28 December 2017 © Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract In this study, we report low and mid temperature range thermoelectric properties of Sb-substituted Cu 2 SnSe 3 compounds. The Cu 2 Sn 1−x Sb x Se 3 (0 ≤ x ≤ 0.04) alloys were prepared using conventional solid-state reaction followed by spark plasma sintering. The crystal structure was characterized using XRD and it reveals that all the samples exhibit cubic structure with space group - 43m. The electrical transport characteristics indicate degenerate semiconducting behavior. Electrical resistivity was found to follow small polaron hopping (SPH) model in the entire temperature range of investigation. The Seebeck coef- fcient data reveals that the majority of charge carriers are holes and the analysis of Seebeck coefcient data gives negative values of Fermi energy indicating that the Fermi energy is below the edge of valence band. The electronic contribution (κ e ) for total thermal conductivity is found to be less than 1%. The maximum ZT value of 0.64 is observed for the sample with x = 0.03 (at 700 K) which is approximately 2.3 times that of the pristine sample. 1 Introduction Thermoelectric energy conversion has received renewed attention in response to the energy and environmental crisis. As a matter of fact, about two-third of all used energy is lost as waste heat. Thermoelectric (TE) materials interconvert heat into electricity and vice versa. The main advantage of TE devices over conventional mechanically driven machines is that they use electrons and holes to perform the work, and thus no moving parts are involved in the process. This makes them favorable for energy conversion in space and cooling applications with high reliability [1–3]. Thermoelectric research is primarily focused to improve conversion ef- ciency which is directly correlated to a dimensionless quan- tity called a thermoelectric fgure of merit, Z, which is defned as ZT = S 2 T  , where S, ρ, κ and T are the Seebeck coefcient, electrical resistivity, thermal conductivity of the materials and absolute temperature respectively. High-performance thermoelectric materials are expected to have large Seebeck coefcient, low electrical resistivity and low thermal conductivity. The higher is the material’s ZT, the greater will be the thermoelectric efciency. To achieve high ZT is a challenging task because S, ρ and κ are interde- pendent for most of the materials, i.e., optimizing one parameter normally has an adverse efect on other parame- ters [4]. There are several approaches to enhance ZT which are broadly aimed to either manipulate electronic structure or efectively reduce thermal conductivity. The semiconductors which belong to the family I 2 –IV–VI 3 found to have appli- cations in various felds like Li-on batteries, and thermo- electrics [5–8]. These compounds have been derived from binary zinc blende type II–VI compounds by considering three unit cells (II 3 –VI 3 ) using the concept of cross substi- tution given by Goodman [9]. It is found that the derived compound shows better thermoelectric performance than the binary compound. In Particular, Cu 2 SnSe 3 which is derived from ZnSe, has low thermal conductivity (~ 27 mW/cmK) as compared to the primary compound ZnSe (~ 190 mW/cmK). Cu 2 SnSe 3 is a p-type semiconductor which has a bandgap 0.8–1.7 eV [10]. There are some controversies regarding the crystal structure of Cu 2 SnSe 3 . Some researchers reported that the Cu 2 SnSe 3 exhibits a cubic phase with space group F - 43m [11, 12], and others reported that Cu 2 SnSe 3 has a monoclinic structure with space group Cc [13, 14]. * Ashok Rao ashokanu_rao@redifmail.com 1 Department of Physics, Manipal Institute of Technology, Manipal Academy of Higher Education, Manipal 576104, India 2 Advance Materials and Devices, CSIR-National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi 110012, India