THE SPONTANEOUS STRAIN IN SRTIO3 IN THE QUANTUM PARAELECTRIC REGIME -THE DEPENDENCE ON SAMPLE PREPARATION

The temperature dependence of the spontaneous strain in SrTiO3 has bee n studied using triple-axis diffractometers of high momentum-space res olution for synchrotron radiation with energies above 100 keV. In the temperature range from 40 to 80 K the experimental data are in excelle nt agreement with a Landau theory taking into account the quantum mech anical zero-point fluctuations. At temperatures below 40 K a differenc e between experiment and theory of about 4% occurs which is considered as an indication for a novel phase in the quantum paraelectric regime . The difference between the fitted theory and the experimental data i s nearly the same for all of the samples investigated; the biggest dif ference is observed in the fit parameter describing the theoretical sa turation value of the spontaneous strain at zero temperature. In absol ute numbers the measured spontaneous strain is strongly sample depende nt, i.e. flux-grown, float-zone-grown and Verneuil-grown crystals show differences in the spontaneous strain of about 30% at 10 K. On the ot her hand, only small variations are observed in samples which were sub jected to different heat treatments, which determine the number of oxy gen vacancies.