Pressure dependence of the Raman modes in Sr₂TiO₄

Sr2TiO4 is an insulator with the same crystal structure as the high temperature superconductor La2-xSrxCuO4. In order to try to better understand these materials, we have studied the effect of hydrostatic pressure on the four allowed Raman modes of Sr2TiO4 up to 7 GPa at room temperature. All modes shift to higher frequencies with increasing pressure. Based on the pressure dependence and bond lengths, we tentatively assign the two high frequency modes to those involving mostly the oxygen motions and the two low frequency ones to those involving primarily the strontium motions. Comparison of mode frequencies in other materials with the same structure is also discussed. © 1987.