Structural change of orthorhombic-I tridymite with temperature: A study based on second-order thermal-vibrational parameters
Abstract
X-ray studies of orthorhombic-I tridymite, especially focussed on atomic mean-square displacements (m.s.d.'s) at 443, 493, 573, 653 and 693 K respectively, were carried out on the basis of the usual second-order refinement of the Dollase model.
The m.s.d.'s for O are highly anisotropic, and large in the planes perpendicular to Si – Si axes. Plots of temperature vs. m.s.d.'s point to a disorder of O atoms in the orthorhombic-I form. The transition, from the orthorhombic-I to the hexagonal high form or vice versa, is an example of a displacive structure transition from a disordered structure to another disordered one. When temperature falls from 693 K, any two SiO4 tetrahedra joined by O on the two-fold axes parallel to a move away from the hexagonal positions, rotating progressively around the two-fold axes, and then symmetry is lowered to orthorhombic. The pair-wise rotations are accompanied by anisotropic changes of the thermal ellipsoids for two kinds of O atoms forming the basal planes of silica tetrahedra, nearly normal to c; the thermal ellipsoids are distorted to elliptical shapes in the sections perpendicular to Si – Si axes when temperature falls. On the other hand, the thermal ellipsoid for the apical O atom is approximately circular in that section.
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Articles in the same Issue
- The crystal structure of ε-Mg2PO4OH, a synthetic high-temperature polymorph
- The crystal structure of β-Mg2PO4OH, a synthetic hydroxyl analogue of wagnerite
- Structural change of orthorhombic-I tridymite with temperature: A study based on second-order thermal-vibrational parameters
- High-order thermal-motion tensor analyses of tridymite
- The crystal structure of the room-temperature phase of AgTaO3
- The crystal structure of [(CH3)2N(CH2)2(CH2)2O]2NaAg3I6 · 2H2O*
- (Z) phényl-1 diéthylaminocarbonyl-1 aminométhyl-2 cyclopropane (Midalcipran): Etude structurale comparative des variétés Cis, Trans I et Trans II
- Crystal structure and spectra of trans-dichloro-p-chlorobenzoyldi-(2-pyridyl)ketonohydrazono antimony(III)
- Orientational disorder in cubic CsNO2 by neutron powder diffraction
- π-character of C(phenyl) – N(amide) bonds in acetanilides and C(phenyl) – C(keto) bonds in acetophenones
- Crystal structure and chirality of sodium tetrathionate dihydrate, Na2S4O6 · 2H2O
- Crystal structure of bismuth selenochloride, BiSeCl
- Crystal growth and physical properties of l-glutamic acid halides, l-c5H9NO4 · HX (X = Cl, Br, I)
- Third-order elastic constants of cubic NaBrO3, Na3SbS4 · 9H2O and NaH(CH3COO)2
- Crystal structure of FePO4 at 294 and 20 K
- Crystal structure of harstigite, MnCa6Be4[SiO4]2[Si2O7]2(OH)2
- Refinement of the crystal structure of tetraphosphorus decaoxide
- Physikalische Kristallographie“,
