  Chromium thiophosphate (CrPS4), a monoclinic crystal of C_2^3 space group, is
a ternary layered semiconductor with an optical bandgap of 1.4 eV and exhibits
antiferromagnetism below 36 K. Despite its potential in optoelectronic and
magnetic applications, the symmetry of its lattice vibrations has not been
systematically studied. In this work, we performed a polarized Raman
spectroscopy of bulk CrPS4 using three different excitation wavelengths of 457,
514, and 633 nm. High-quality crystals grown by the chemical vapor transport
method were mechanically exfoliated or polished to expose three orthogonal
crystallographic facets. Polarized Raman spectra were obtained in parallel and
cross configurations by rotating samples about the surface normal to each of
the facets. Among 33 Raman active modes (16 A and 17 B) at the Brillouin zone
center, 19 (8) peaks observed in the parallel (cross) configuration were
assigned as A (B) modes. Complex-valued Raman tensors were determined for 7
major A modes using the angle-dependent Raman spectra of the three facets. The
results can also be used in determining the crystallographic orientations of
CrPS4 unequivocally.
