Variable–temperature single–crystal X–ray diffraction study of SrGeO₃ high–pressure perovskite phase

抄録

Single–crystal X–ray diffraction analysis of a high–pressure cubic perovskite SrGeO₃ was conducted for a temperature range of 100 to 473 K. The crystal structure begins to deteriorate at a temperature higher than 323 K and completely amorphizes by 448 K. Structure refinements in a range of 100 to 323 K show that the displacement ellipsoid of the O atom is considerably suppressed in the direction of the Ge–O bond and that its mean square displacement (MSD) in this direction is almost temperature–independent. In contrast, that in the direction perpendicular to the bond largely increases with the temperature. The Debye temperatures for each constituent atom were determined by applying the Debye model to the temperature dependence of its MSDs. The one–particle potential (OPP) coefficient evaluated from the resulting Debye temperature of the Ge atom is significantly larger than those of the Sr and O atoms. Moreover, the OPP coefficients of the O atom are significantly larger in the direction of the Ge–O bond than in the directions perpendicular to the bond. These results are concordant with our previous finding that the Ge–O bond is largely covalent. The high covalency can have a large influence on the temperature dependence of the thermal vibration of the O atom.