We present an in-depth first-principles study of the lattice dynamics of the tin sulphides SnS2, Pnma and π-cubic SnS and Sn2S3. An analysis of the harmonic phonon dispersion and vibrational density of states reveals phonon bandgaps between low- and high-frequency modes consisting of Sn and S motion, respectively, and evidences a bond-strength hierarchy in the low-dimensional SnS2, Pnma SnS and Sn2S3 crystals. We model and perform a complete characterisation of the infrared and Raman spectra, including temperature-dependent anharmonic linewidths calculated using many-body perturbation theory. We illustrate how vibrational spectroscopy could be used to identify and characterise phase impurities in tin sulphide samples. The spectral linewidths are used to model the thermal transport, and the calculations indicate that the low-dimensional Sn2S3 has a very low lattice thermal conductivity, potentially giving it superior performance to SnS as a candidate thermoelectric material.
Bibliographical noteFunding Information:
JMS gratefully acknowledges support from the Engineering and Physical Sciences Research Council (EPSRC) (grant no. EP/K004956/1 and EP/P007821/1). LAB is an International Research Fellow of the Japan Society for the Promotion of Science (JSPS; grant no. 26.04792). AW is grateful for support from the Royal Society and the EPSRC (grant no. EP/M009580/1). Calculations were carried out on the Balena HPC cluster at the University of Bath, which is maintained by Bath University Computing Services, and on the SiSu supercomputer at the IT Center for Science (CSC), Finland, via the Partnership for Advanced Computing in Europe (PRACE) project no. 13DECI0317/IsoSwitch. Some of the calculations were also carried out on the UK national Archer HPC facility, accessed through membership of the UK Materials Chemistry Consortium, which is funded by EPSRC grant no. EP/L000202.
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