New Monoclinic Phase at the Composition Cu₂SnSe₃ and Its Thermoelectric Properties

Abstract

A new monoclinic phase (m2) of ternary diamond-like compound Cu2SnSe3 was synthesized by reaction of the elements at 850 K. The crystal structure of m2-Cu2SnSe3 was determined through electron diffraction tomography and refined by full-profile techniques using synchrotron X-ray powder diffraction data (space group Cc, a = 6.9714(2) Å, b = 12.0787(5) Å, c = 13.3935(5) Å, β = 99.865(5)°, Z = 8). Thermal analysis and annealing experiments suggest that m2-Cu2SnSe3 is a low-temperature phase, while the high-temperature phase has a cubic crystal structure. According to quantum chemical calculations, m2-Cu2SnSe3 is a narrow-gap semiconductor. A study of the chemical bonding, applying the electron localizability approach, reveals covalent polar Cu-Se and Sn-Se interactions in the crystal structure. Thermoelectric properties were measured on a specimen consolidated using spark plasma sintering (SPS), confirming the semiconducting character. The thermoelectric figure of merit ZT reaches a maximum value of 0.33 at 650 K.

Crystal Structure and Physical Properties of Ternary Phases around the Composition Cu5Sn2Se7 with Tetrahedral Coordination of Atoms

“…40 According to our recent investigation, the phase Cu 2 SnSe 3 crystallizes in the monoclinic-II structure with its own structure type (space group Cc) at low temperature and in the cubic sphalerite-type structure (space group F4̅ 3m) at elevated temperature. 16 Cu 5 Sn 2 Se 7 and Cu 4.9 Sn 2.1 Se 7 are both superstructures to the cubic sphalerite-type Cu 2 SnSe 3 . The presence of a common cubic substructure is demonstrated by the appearance of the strong reflections representing a face-centered lattice (space group F4̅ 3m) with a c ≈ 5.66 Å in the X-ray powder diffraction patterns of the new phases (Figures 4 and 5).…”

“…15 On the basis of intrinsically low lattice thermal conductivity of Cu-based chalcogenides, discovery of new ternary selenides may provide further opportunities for band structure engineering and tunable electrical properties. According to our previous experience with Cu 2 SnSe 3 , 16 in the Cu−Sn−Se system it is often difficult to obtain high quality single crystals suitable for structural analysis because of the appearance of twinning. As an alternative, electron diffraction tomography 17 combined with high-resolution synchrotron Xray diffraction is a suitable tool for the determination of the crystal structure of new compounds using crystalites with a size of 100−400 nm.…”

Copper chalcogenide thermoelectric materials

“…Cu 2 SnSe 3 can crystallize into a cubic (F-43m) or monoclinic phase (three types [140]) at room temperature. A high zT of 1.14 at 850 K was achieved via In substitution for Sn by Shi et al [39].…”

“…Binary and ternary Figure 13 Crystal structure of (a) Cu 2 SnSe 3 (reproduced from Ref. [140] REVIEWS . .…”

Single nano crystal analysis using automated electron diffraction tomography

“…The success of ADT has encouraged other groups to develop their own systems for tomographic acquisition of electron diffraction data (Palatinus et al 2011;Gemmi et al 2012;Fan et al 2013;Cora et al 2014). A promising alternative experimental setting was proposed with the rotation electron diffraction (RED) method, where mechanical sample tilt is supplemented by beam tilt for a finer reciprocal space sampling (Zhang et al 2010).…”