Elastic relaxations associated with the Pm̄3m-R̄3c transition in LaAlO₃: I. Single crystal elastic moduli at room temperature

Values for all six independent components of the ̄3m elastic modulus tensor of LaAlO₃ perovskite are reported. These were determined by means of Brillouin scattering measurements of acoustic velocities in single crystal plates cut parallel to (110) and (100), as defined with respect to the cubic parent structure, and by pure-mode longitudinal and transverse sound velocity measurements along [100], [110] and [111] directions using GHz pulse-echo ultrasonics. The crystals contained intimate intergrowths of twins arising from the Pm̄3m→R̄3c transition at higher temperature but, in combination with a careful analysis of twin orientation relationships, the two sets of data have allowed a unique solution to be obtained for individual twin components. The new data set represents an important contribution to the characterization of LaAlO₃ single crystals which are widely used as the substrate for a plethora of different thin films with technological applications.