Cubic to tetragonal phase transition of SrTiO3 under epitaxial stress: An X-ray backscattering study

Employing synchrotron radiation in backscattering geometry we studied the 1 05 K cubic to tetragonal (CT) phase transition of SrTiO3 by X-ray diffracti on using the (006) reflection of three (001) oriented samples. Two of the c rystals were covered with ultra-thin films of YBa2Cu3O7-delta (14 nm) and G dBa2Cu3O7-delta (28 nm), respectively. We find that the stress induced by t he epitaxial layers influences the behavior of the CT transition in two way s. (i) The critical temperature increases by 1.2 K as a result of the homog eneous epitaxial stress (13.5 MPa) introduced into the substrate by the pse udomorphic GdBa2Cu3O7-delta film. (ii) Strain affects the critical exponent of the temperature dependence of the order parameter. Furthermore, the mic rostructure of the tetragonal domains and its temperature dependence are ma rkedly different for the three samples.