Pressure-induced phase transition in LaAlO₃

We report on a study of pressure-dependent structural properties of LaAlO₃, which is considered to be a model material of the class of `tilted' perovskites. Our high-pressure investigation by means of Raman spectroscopy and synchrotron radiation shows that LaAlO₃ presents structural instabilities under pressure and undergoes a soft-mode-driven rhombohedral-to-cubic phase transition in the vicinity of 14 GPa, which can be analysed in the framework of a Landau model. The structural changes are described in terms of a collective restoring of the initially tilted AlO₆ octahedra towards the ideal cubic perovskite structure without tilting. Up to 40 GPa, the pressure dependence of the volume of the pseudo-cubic phase is described by a third-order Birch-Murnaghan equation of state with parameters V₀ = 54.57(4) Å³, K_T = 190(5) GPa and K' = 7.2(4).