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

Abstract

Single-crystal X-ray diffraction analysis of a high-pressure cubic perovskite SrGeO 3 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.

Detailed Structural Features of the Perovskite-Related Halide RbPbI3 for Solar Cell Applications

“…The Debye model is supposed to describe the temperature evolution of the MSDs, as summarized below where such that d s 2 is the intrinsic disorder, θ D is the Debye temperature, m is the atom’s mass, and T , k B , and ℏ keep their usual meaning. 34 , 35 As low-temperature points (<100 K) were not taken, the uncertainty associated with d s 2 is high, when it is considered as a fitting parameter. In order to avoid this, such a parameter was kept equal to zero for all the atoms (Rb, Pb, I1, I2, and I3).…”

“… 36 The bonding stiffness may be evaluated from the Debye temperature by considering the harmonic one-particle potential (OPP). 34 Here, the harmonic potential is written as V opp ( d D 2 ) = 1/2 Kd D 2 , where …”

Shallow Valence Band of Rutile GeO2 and P-type Doping

“…13 The single crystal growth of cubic SrGeO3 was recently demonstrated and a remarkably high 3.9 ± 0.5 × 10 2 cm 2 /Vs intrinsic RT mobility was derived from the polarization and frequency of optical phonons. 18 However, because the successful synthesis requires 5-GPa high pressure conditions, and the crystalline-to-amorphous transition already occurs at temperatures as low as 100 o C at ambient pressure (AP), 19 the practical application of cubic SrGeO3 is greatly limited. Thus, we target the exploration of AP-stable WBG oxides that can be employed as electronic conductors.…”

Aluminous hydrous magnesium silicate as a lower-mantle hydrogen reservoir: a role as an agent for material transport

“…Even if unique reflections had intensities of after averaging, those averaged from data set of equivalent reflections including reflection(s) with were also discarded since these reflections were potentially affected by multiple scattering as in Refs. 51 – 56 . Finally, 167 unique reflections were used in the present refinements.…”