Study of point defects and phase transitions in undoped and Nb-doped SrTiO3 using perturbed angular correlations

Recovery of point defects and local phase transitions were studied in the neighbourhood of implanted 111mCd (low fluence of 1.5 × 1012 at/cm2) into undoped and 2%Nb-doped SrTiO3 single crystals by means of the perturbed angular correlation technique. Measurements in the as implanted state and after subsequent 720 °C and 1000 °C 20 min air annealings have shown the recovery of defects in the Cd neighbourhood. After annealing, low temperature experiments have studied the cubic-to-tetragonal and the orthorhombic-to-rhombohedral phase transitions at the atomic scale. In the undoped samples it was found at 77 K, the coexistence of cubic and tetragonal single oriented phases. By further cooling the samples to 10 K a single low – symmetry phase is formed. On Nb-doped samples the phase transitions are hindered, being the lattice symmetries also affected in the Cd atomic neighbourhood. These effects appear to be particularly dependent on the dopant concentration.