The crystal structure of low tridymite

Konnert, J. H.; Appleman, Daniel E.

doi:10.1107/s0567740878003210

Cited by 88 publications

(48 citation statements)

References 9 publications

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“…Unlike the arrowed reflections, those of the type labelled A and B do not exactly form rows parallel to hexagonal c*; they are incommensurate, and form pairs of satellites about the other (subcell) reflections. It is possible to estimate lattice parameters for MX, using the superimposed PO patterns for calibration and assuming that PO has the lattice parameters given by Konnert and Appleman (1978). Within the uncertainties expected in electron diffraction (approximately 1%), both the parameters of the sublattice and the positions of the satellite reflections agree with those reported by Hoffmann et al (1983).…”

Section: Electron-diffraction Characteristics Of Polymorphssupporting

confidence: 75%

“…Kato and Nukui (1976) Konnert and Appleman (1978) HoIlmann et al (1983) interpretation of polymorph distribution, specifically the PO/cristobalite association.…”

Section: Methodsmentioning

confidence: 99%

“…53, pp. 89 97 (~ Copyright the Mineralogical Society investigated by Konnert and Appleman (1978), is one of a range of pseudo-orthorhombic tridymites PO-n, where n is the multiplicity (relative to hexagonal tridymite) of the c repeat (Wennemer and Thompson, 1984;Carpenter and Wennemer, 1985). In a TEM study of various synthetic tridymites, Carpenter and Wennemer (1985) identified MC and PO-n (n = 3, 4, 5, and 6); they also defined a 'pseudohexagonal' tridymite which may be the same as MX, though they were unable to confirm subtle details which would be predicted from the XRD results of Hoffmann et al (1983).…”

Section: Introductionmentioning

confidence: 99%

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Transmission electron microscopy of coexisting low-tridymite polymorphs

Ashworth¹

1989

Mineral. mag.

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Three polymorphs of tridymite (MC, PO-10 and MX) have been examined by transmission electron microscopy (TEM), in crystals which also contain lamellae of cristobalite. MX is the least common, and is highly unstable in the electron beam. It occurs as small regions (< 1 /~m 2) in PO-10 tridymite and at MC/PO-10 boundaries; these regions are interpreted as being strained. A consistent association between PO-10 and the cristobalite lamellae is attributed to the fact that PO-10 can more closely match the low-cristobalite structure than MC can, at boundaries parallel to the plane in which the crystal structures contain layers of SiO4 tetrahedra. An analogous interpretation explains the observation that twin boundaries (associated with 60 ~ or 120 ~ rotation of the layer) are commonly parallel to the layer plane in PO-10 but at high angles to it in MC. Abundant lamellar features, parallel to the same plane in PO-10, are tentatively interpreted as representing twinning by reflection and 180 ~ rotation, which may also account for c* streaking in diffraction patterns.

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Section: Electron-diffraction Characteristics Of Polymorphssupporting

confidence: 75%

“…Kato and Nukui (1976) Konnert and Appleman (1978) HoIlmann et al (1983) interpretation of polymorph distribution, specifically the PO/cristobalite association.…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Transmission electron microscopy of coexisting low-tridymite polymorphs

Ashworth¹

1989

Mineral. mag.

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“…The silica polymorphs in the data set besides P2 ~/a coesite are synthetic tridymite (Baur, 1977), low quartz (Zachariasen & Plettinger, 1965), low cristobalite (Dollase, 1965) and C2/c coesite (Gibbs, Prewitt & Baldwin, 1977). Not added were the data on terrestrial tridymite (Konnert & Appleman, 1978), even though this structure alone has.160 O atoms in the asymmetric unit. The reason for omitting it is that it was refined with the restrained-parameter structurefactor least-squares method (Konnert, 1976) in which predicted interatomic distances are used as observations along with X-ray diffraction data.…”

Section: Datamentioning

confidence: 99%

Straight Si–O–Si bridging bonds do exist in silicates and silicon dioxide polymorphs

Baur¹

1980

Acta Crystallogr Sect B

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“…This is unlikely since it would mean the creation of energetically unfavourable Si-O-Si angles of 180 ~ The relationship between ordered high-tridymite and the roomtemperature structures is much more complex. Recent structural studies at room temperature (Dollase and Baur, 1976;Kato and Nukui, 1976;Baur, 1977;Konnert and Appleman, 1978) have revealed complicated superstructures made up of different stacking sequences of at least two distorted forms of a single 'layer' of the idealized high-tridymite structure. These complicated structures exhibit strong hexagonal pseudosymmetry and twinning leading to difficulties in structure determinations possibly accounting for the earlier reports of orthorhombic or hexagonal roomtemperature tridymite.…”

Section: Framework Structures Without Cavity Ions: Each Shared Vertexmentioning

confidence: 99%

The structural behaviour of tetrahedral framework compounds — a review Part II. Framework structures

Taylor¹

1984

Mineral. mag.

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ABSTRACT. Tetrahedral framework compounds, as defined in this paper, generally exist as tilted and distorted versions of ideal fully expanded structures'at room temperature and atmospheric pressure. How pressure, temperature, and composition (P, T, and X) affect the tilting and distortion is critically reviewed. It is shown that although the effects of P, T, and X on the cell parameters are broadly analogous, the underlying structural changes are generally different. An important, and frequently neglected thermal effect is the apparent shortening of the framework bonds by the anisotropic thermal motion of the framework oxygens. Tilting models of framework compounds are critically examined and their failure to match the observed structural behaviour is attributed to changes in tetrahedral distortion. For quartz it appears that during compression the change in tetrahedral distortion is virtually all angular (O-Si-O angles), whereas during thermal expansion the change in distortion is in the Si-O distances. Such behaviour may typify the behaviour of many other framework compounds but the structural data needed to establish this are lacking. The review is illustrated by reference to the quartz and cristobalite analogues; to the sodalite, leucite, nepheline, scapolite, and feldspar families; and to the nitrides and oxynitrides of silicon and germanium. It is concluded that our understanding of the structural behaviour of framework compounds is still superficial and that much theoretical and experimental work remains to be done.

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The crystal structure of low tridymite

Cited by 88 publications

References 9 publications

Transmission electron microscopy of coexisting low-tridymite polymorphs

Transmission electron microscopy of coexisting low-tridymite polymorphs

Straight Si–O–Si bridging bonds do exist in silicates and silicon dioxide polymorphs

The structural behaviour of tetrahedral framework compounds — a review Part II. Framework structures

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