IOP PUBLISHING JOURNAL OF PHYSICS: CONDENSED MATTER J. Phys.: Condens. Matter 22 (2010) 035403 (11pp) doi:10.1088/0953-8984/22/3/035403 Elastic relaxations associated with the Pm ¯ 3m–R ¯ 3c transition in LaAlO 3 : I. Single crystal elastic moduli at room temperature M A Carpenter 1 , S V Sinogeikin 2 , J D Bass 2 , D L Lakshtanov 2,4 and S D Jacobsen 3 1 Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK 2 Department of Geology, University of Illinois, Urbana, IL 61801, USA 3 Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL 60208, USA E-mail: mc43@esc.cam.ac.uk Received 1 August 2009, in final form 14 October 2009 Published 21 December 2009 Online at stacks.iop.org/JPhysCM/22/035403 Abstract Values for all six independent components of the ¯ 3m elastic modulus tensor of LaAlO 3 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 Pm ¯ 3m ↔ R ¯ 3c 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 LaAlO 3 single crystals which are widely used as the substrate for a plethora of different thin films with technological applications. 1. Introduction LaAlO 3 is currently one of the most important single crystal substrate materials for the growth of thin films with diverse physical, chemical and electronic properties. Some of the criteria involved in the choice of substrate material to support superconducting thin films were set out by Phillips (1996) and many of the earlier applications were for the cuprate superconductors, including YBa 2 Cu 3 O 7−δ (e.g., Simon et al 1988). LaAlO 3 can also be used in thin-film form itself, either intergrown with the superconductor (e.g., Lee et al 1990) or for its high-k dielectric properties on a Si substrate (e.g., Xiang et al 2003). More recently, LaAlO 3 single crystals have been used to support ferroelectric thin films such as BaTiO 3 4 Present address: BP Labs, 200/55 Chertsey Road, Sunbury on Thames, TW16 7BP, UK. (Zhu et al 2006) and (Ba, Sr)TiO 3 (Liu and Jiang 2006), manganite thin films for their electrical characteristics (e.g., Masuno et al 2004, Lehmann et al 2007) or other perovskite thin films with progressively more complex structures (e.g., Masuno et al 2006). This expanding list of applications has also resulted in a flurry of computational studies of structural, physical and defect properties (Peacock and Robertson 2002, Delugas et al 2005, Shevlin et al 2005, Xiong et al 2006, Luo and Wang 2008a, 2008b, Vali 2008). Given that many of the applications depend to some extent on elastic thin film–substrate interactions, it is surprising that there appear to have been no experimental determinations of the elastic moduli of LaAlO 3 . The bulk modulus is known from high pressure equation of state measurements (Bouvier and Kreisel 2002, Zhao et al 2004), but the present authors have not been able to find values in the literature for the shear modulus or 0953-8984/10/035403+11$30.00 © 2010 IOP Publishing Ltd Printed in the UK 1