TETRAGONAL TO CUBIC PHASE TRANSITION IN Sr0.75Ba0.25HfO3.

C. HOROWITZ; R. E. ALONSO; A. LÓPEZ GARCÍA

FERROELECTRICS

Año: 2002 vol. 269 p. 117 - 124

0015-0193

Using powder X-Ray Diffraction and Perturbed-Angular-Correlation spectroscopy, the crystal structure and the hyperfine interaction at 181Ta probe in Sr0.75Ba0.25HfO3 have been studied. A tetragonal (I4/mcm) to cubic (Pm m) phase transition was observed. A two-phase field region, where the tetragonal and cubic phases coexist, was found between 673 and 923 K. The spin precession curves were measured from room temperature up to 1373 K. A static, asymmetric and disordered electric field gradient model was used to fit these time spectra. The hyperfine parameters corresponding to the tetragonal structure changed as the temperature increases: wTQ diminishes, hT is almost constant and dT diminishes. This interaction was observed to be unique up to 673 K. Above this temperature, a second interaction appeared and these two phases coexist up to 923K. Above this temperature, the hyperfine parameters corresponding to the cubic structure was only observed. The tetragonal to cubic transformation is characterized by an activation energy of about 0.62 eV.