Stress-induced changes in the Raman spectrum of paratellurite

Abstract

We studied the effect of uniaxial stress on the Raman spectrum of paratellurite, at room temperature. The observed changes are interpreted using a linear-deformation-potential theory that has been successfully applied in a wide variety of materials. This theory describes well the behavior of all observed lines when the force is applied along the [001] and [110] crystallographic directions. The shifts and splittings obtained when stress is applied along the [100] direction, however, are much larger than those expected on the basis of the aforementioned theory. This anomaly is stronger for the lowest-frequency $B_1$ line which exhibits a strong supra-linear frequency increase for [100] stress. The anomalous behavior for [100] stress is believed to be due to the $D_4^4\to D_2^4$ structural phase transition that takes place in paratellurite under hydrostatic stress, since a [100] stress produces a distortion of the same symmetry as the one responsible for the transition. Deformation-potential values for representative modes are obtained from measurements of pure modes and quasi modes and Grüneisen parameters calculated from these deformation potentials are in good agreement with those previously obtained from hydrostatic-pressure measurements.