Analysis of stress and temperature dependence of fluorescence in SrTiO3 : Cr3+

We write a configurational potential for SrTiO3 which depends on strain and the soft optic-mode coordinates whose wave vector lies at the corner of the Brillouin zone. Minimizing this potential gives the static response of the crystal to applied stress. Below the cubic-to-tetragonal transition temperature at 106 degrees K, uniaxial stress applied in the [111] direction induces a transition from the natural tetragonal to a trigonal phase, but transitions for [100] and [110] stresses are not found. A crystal-field calculation gives the R-line emission energy of Cr3+ impurities. The results fit the temperature-dependence anomaly found by Stokowsky and Schawlow and, within limits, the pressure dependence found by Burke and Pressley. However, pronounced discrepancies appear at stresses along the [100] and [110] directions which exceed critical values of 10 and 57 kg/mm(2), respectively, suggesting that new phases of unknown character appear. The crystal-field parameter values inferred from the comparison with experiment support the nearest-neighbor approximation for the cubic component of the crystal-field, but not for lower-symmetry components. Our calculations disagree with a reported measurement of the stress dependence of the transition temperature.