The crystal structure of β-beryllia

Smith, D. K.; Cline, C.F.; Austerman, S.B.

doi:10.1107/s0365110x65000877

Cited by 76 publications

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“…In BCT the alignment between ab layers is the same but the ab rings adopt boat conformations arranged back-to-back to give a characteristic topology of alternating four-and eight-membered rings. 8 A third related structure is h-MgO, where the ab six-membered rings are flat hexagons, giving a local ͓3+2͔ coordination ͑Fig. 1͒.…”

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“…9 BCT has been predicted as a stable phase in theoretical simulations of materials such as ZnO and ZnS in nanocrystals, 10,11 free-standing thin films, 12 and nanorods under tensile strain. 13 The BCT structure is seen for the hightemperature ␤-BeO phase, 8 and has recently been stabilized in ZnS nanocrystals grown via chemical coprecipitation, to produce samples with enhanced visible photoluminescence. 14 BCT may also exhibit desirable mechanical and electronic properties: Wang et al 15 have predicted that for ZnO BCT has a lower elastic modulus than B4 and that both the band gap and electron effective mass are reduced.…”

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First-principles study of epitaxial strain as a method ofB4→BCTstabilization in ZnO, ZnS, and CdS

Morgan

2010

Phys. Rev. B

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Density-functional-theory calculations have been used to examine stabilization of the low density BCT polymorph by epitaxial strain. The relative energies of B4 and BCT polymorphs were calculated for ZnO, ZnS, and CdS, as a function of epitaxial strain, for a B4 ͓0001͔ ʈ BCT ͓010͔ / B4 ͓1210͔ ʈ BCT ͓001͔ correspondence. The phase stability is mapped in ͕u , v͖ parameter space and the challenge of identifying a suitable epitaxial support to direct growth of the BCT phase is discussed. For ZnS, ZnSe, ZnTe, CdS, and CdSe, the optimized "BCT" geometry is orthorhombically distorted, in contrast to the tetragonal lattices of ZnO, CdO, and InN. This orthorhombic distortion is associated with a rotation of the four-membered rings in the BCT structure, and is enhanced in ZnO, ZnS, and CdS under epitaxial strain.

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First-principles study of epitaxial strain as a method ofB4→BCTstabilization in ZnO, ZnS, and CdS

Morgan

2010

Phys. Rev. B

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“…TBSs have been generally prepared in only two tetrahedral polymorphs (wurtzite and zincblende), a number of intergrowths in between these two (so-called polytypes [12]) and at high pressure as the octahedral rocksalt polymorph [13,14]. Only one further polymorph is observed for TBSs experimentally: the -BeO or BCT structure (where the three letter code, here and throughout, refers to an International Zeolite Association framework type [15]), as displayed by BeO (i.e., BCT-BeO) at high temperatures [16], sharing the same 4CN as the silicate Mg-BCTT .Previous theoretical work addressing the energy landscape of TBSs has identified a number of hypothetical polymorphs, many of which lie much higher in energy than wurtzite and zincblende. The two lowest energy PRL 104, 175503 (2010) …”

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Apparent Scarcity of Low-Density Polymorphs of Inorganic Solids

2010

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For most inorganic solids, very few dense polymorphs and no low-density polymorphs are observed. Taking a wide range of tetrahedrally-coordinated binary solids (e.g., ZnO, GaN) as a prototypical system, we show that the apparent scarcity of low-density polymorphs is not due to significant structural or energetic limitations. Using databases of periodic networks as sources of novel crystal structures, followed by ab initio energy minimization, we predict a dense spectrum of low-density low-energy polymorphs. The diverse range of materials considered indicates that this is likely to be a general phenomenon. DOI: 10.1103/PhysRevLett.104.175503 PACS numbers: 61.50.Ah, 61.66.Fn, 71.15.Nc, 82.75.Fq The structure and properties of inorganic solids are intimately linked to such an extent that even different structures of the same composition (so-called polymorphs) often have widely differing properties and applications. For boron nitride (BN), for example, the soft hexagonal layered polymorph (h-BN) is used as a lubricant, while the cubic polymorph (wurtzite structure) is extremely hard and is employed as an industrial abrasive. Germanium also exhibits more than one polymorph (or more strictly ''allotrope'' for elemental systems) having very different optical properties; with the diamond structured -germanium having an indirect band gap, and the recently synthesized lowdensity clathrate-II structure [1] a direct gap. Evidently, having access to more than one polymorph can significantly extend the range of properties and applications of a particular compound. For the vast majority of inorganic solids, however, typically only three or fewer distinct polymorphs have been prepared experimentally and a similarly small number of hypothetical polymorphs have been proposed. Moreover, where more than one polymorph is known, these extra phases very rarely have a significantly lower density than the most stable polymorph.In stark contrast to this situation, silica (SiO 2 ) has been prepared as more than 40 polymorphs [2], the majority of which are considerably less dense than -quartz; the most stable polymorph under ambient conditions. The rich polymorphism of silica, especially in its low-density forms, allows for fine-tuning of applications (e.g., gas separation membranes) by choosing the best suited polymorph. In addition, 100 000þ hypothetical silica polymorphs have been predicted theoretically as fourfold-connected networks (4CNs) [3][4][5][6][7], a large fraction of which, after accurate theoretical evaluation as silica materials, were found to have comparable energetics to experimentally prepared polymorphs [8,9]. Similarly rich polymorphism has only been further observed for a select group of other inorganic solids, for example, aluminophosphates (AlPO 4 ). A tantalizing hint that there may as yet exist a greater pool of experimentally accessible polymorphs for many other inorganic solids is given by the recent low temperature deposition synthesis of the tetrahedral wurtzite polymorph of LiBr [10] (after previous theor...

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“…The structure is also related to the four-connected networks of -BeO (Smith et al, 1965), CrB 4 (Andersson & Lundströ m, 1968), anorthite (CaAl 2 Si 2 O 8 ; Takeuchi et al, 1973) and the AlP sub-arrays of two polymorphs of AlPO 4 Á2H 2 O (the minerals variscite and metavariscite; Kniep & Mootz, 1973;Kniep et al, 1977;Kniep, 1978). In all these structures, represented in Fig.…”

Section: Extended Zintl-klemm Conceptmentioning

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Compounds with a `stuffed' anti-bixbyite-type structure, analysed in terms of the Zintl–Klemm and coordination-defect concepts

Vegas

Martin

Bevan

2008

Acta Crystallogr Sect B

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The bixbyite structure (Mn2O3) (Ia\bar 3) is often described as a distorted face-centered cubic (f.c.c.) array of Mn atoms, with O atoms occupying 3/4 of the tetrahedral holes. The empty M 4 tetrahedra are centred at 16c. In anti-bixbyite structures (Mg3N2), cation vacancies are centred in empty N4 tetrahedra. If 16 hypothetical atoms were located at this site they would form the structure of γ-Si. This means that anti-bixbyite structures are ideally prepared to accommodate Si(Ge) atoms at these holes. Several compounds (Li3AlN2 and Li3ScN2) fully satisfy this expectation. They are really anti-bixbyites `stuffed' with Al(Sc). The presence of these atoms in 16c is illuminated in the light of the extended Zintl–Klemm concept (EZKC) [Vegas & García-Baonza (2007). Acta Cryst. B63, 339–345], from which a compound would be the result of `multiple resonance' pseudo-structures, emerging from electron transfers between any species pair (like or unlike atoms, cations or anions). The coordination-defect (CD) concept [Bevan & Martin (2008). J. Solid State Chem. 181, 2250–2259] is also consistent with the EZKC description of the pseudo-structures. A more profound insight into crystal structures is gained if one is not restricted to the contemplation of classical anions and cations in their conventional oxidation states.

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The crystal structure of β-beryllia

Cited by 76 publications

References 1 publication

First-principles study of epitaxial strain as a method ofB4→BCTstabilization in ZnO, ZnS, and CdS

First-principles study of epitaxial strain as a method ofB4→BCTstabilization in ZnO, ZnS, and CdS

Apparent Scarcity of Low-Density Polymorphs of Inorganic Solids

Compounds with a `stuffed' anti-bixbyite-type structure, analysed in terms of the Zintl–Klemm and coordination-defect concepts

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