Secondary phase Cu2SnSe3 vs. kesterite Cu2ZnSnSe4: similarities and differences in lattice vibration modes

The crystal structure of monoclinic semiconductor Cu2SnSe3 is optimized, in a first-principles LDA calculation by Siesta method, to be found in good agreement with available experimental data, on which base zone-center transversal phonon modes are further calculated. The comparison with a similar calculation for kesterite-phase Cu2ZnSnSe4 helps to identify vibration modes promising to serve as fingerprints for discrimination of these two materials from their lattice-dynamical properties. Moreover, a full analysis of vibration modes is done, which emphasizes an importance of structural motives present in Cu2SnSe3 but absent in kesterite, namely continuous planar chains and stripes of like cations/anions, for the manifestation of structure-specific vibration lines.