Optical reflection and absorption spectra of SrTe and BaTe have been measured in the pressure range of 0 to 400 kbar and 300 K. Excitonic transitions related to the lowest direct gap in the rocksalt (B1) structure shift to lower energy with increasing pressure and are attributed to a Te 5p to Ba 5d (Sr 4d) transition at the X point. In both SrTe and BaTe the optical response indicates a discontinuous decrease of the lowest direct gap by about 1 eV at the pressure-induced structural transitions from the B1 to the B2 (CsCl-type) structure. The direct optical gap of BaTe (B2) closes at pressures near 270 kbar. An upper limit of about 550 kbar is extrapolated for the corresponding band overlap in SrTe. Experimental and previous theoretical results for phase stability, deformation potentials, and metallization in BaTe are compared to fully relativistic self-consistent band-structure calculations using the linear muffin-tin-orbital method in conjunction with the local-density approximation.
 

Physical Review B, 35 4052-9, 1987.