Twinning and epitaxial growth of taaffeite-type modulated structures in BeO-doped MgAl2O4

Drev, Sandra; Rečnik, Aleksander; Daneu, Nina

doi:10.1039/c3ce26997c

Cited by 17 publications

(21 citation statements)

References 18 publications

(54 reference statements)

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“…Furthermore, some reported natural (111) TBs in spinel are chemically induced by incorporation of Be 2+ that replaces Mg 2+ on the tetrahedral sites in the local h.c.p. stacking, as demonstrated by Daneu et al (2007), Drev et al (2013). Here, the TB is free from any dopant.…”

Section: Comparison Of Early and Late Growth Stagessupporting

confidence: 73%

“…10). The main feature of these TBs is their mirror symmetry, which is fundamentally different from the atomic structure of chemically induced TBs formed in natural spinel, such as reported from Be-doped MgAl 2 O 4 (Daneu et al, 2007;Drev et al, 2013), where the twinning is accomplished by 180 rotation around the [111] axis. It is also different from the twin structure reported in other spinel structures, such as twins in magnetite (Gilks et al, 2016).…”

Section: Comparison Of Early and Late Growth Stagesmentioning

confidence: 92%

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Structure evolution of h.c.p./c.c.p. metal oxide interfaces in solid-state reactions

Habler

Griffiths

et al. 2018

Acta Crystallogr A Found Adv

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The structure of crystalline interfaces plays an important role in solid-state reactions. The AlO/MgAlO/MgO system provides an ideal model system for investigating the mechanisms underlying the migration of interfaces during interface reaction. MgAlO layers have been grown between AlO and MgO, and the atomic structure of AlO/MgAlO interfaces at different growth stages was characterized using aberration-corrected scanning transmission electron microscopy. The oxygen sublattice transforms from hexagonal close-packed (h.c.p.) stacking in AlO to cubic close-packed (c.c.p.) stacking in MgAlO. Partial dislocations associated with steps are observed at the interface. At the reaction-controlled early growth stages, such partial dislocations coexist with the edge dislocations. However, at the diffusion-controlled late growth stages, such partial dislocations are dominant. The observed structures indicate that progression of the AlO/MgAlO interface into AlO is accomplished by the glide of partial dislocations accompanied by the exchange of Al and Mg cations. The interface migration may be envisaged as a plane-by-plane zipper-like motion, which repeats along the interface facilitating its propagation. MgAlO grains can adopt two crystallographic orientations with a twinning orientation relationship, and grow by dislocations gliding in opposite directions. Where the oppositely propagating partial dislocations and interface steps meet, interlinked twin boundaries and incoherent Σ3 grain boundaries form. The newly grown MgAlO grains compete with each other, leading to a growth selection and successive coarsening of the MgAlO grains. This understanding could help to interpret the interface reaction or phase transformation of a wide range of materials that exhibit a similar h.c.p./c.c.p. transition.

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Section: Comparison Of Early and Late Growth Stagessupporting

confidence: 73%

Section: Comparison Of Early and Late Growth Stagesmentioning

confidence: 92%

Structure evolution of h.c.p./c.c.p. metal oxide interfaces in solid-state reactions

Habler

Griffiths

et al. 2018

Acta Crystallogr A Found Adv

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“…This operation generates a local hcp stacking, similar to that observed in chrysoberyl, in an otherwise perfect ccp lattice. Furthermore, it has been shown that twinning in spinel is accompanied by replacement of Mg 2+ with Be 2+ on tetrahedral sites adjacent to hcp planes in the O-sublattice (Daneu et al 2007a;Drev et al 2013), demonstrating that twinning is in fact chemically induced (Takeuchi 1997), which further facilitates the structural relationship between spinel and chrysoberyl. As a result of such structural (ccp → hcp) and chemical (Mg 2+ → Be 2+ ) modulation, a range of minerals belonging to polysomatic taaffeite series exists between the two end-compounds: Be 2 Mg 2 Al 8 O 16 (Anderson et al 1951), BeMg 3 Al 8 O 16 (Moor et al 1981), BeMg 2 Al 6 O 12 (Schmetzer 1981), and Be 1.33 Mg 2.67 Al 8 O 16 (Schmetzer 1983) with general formula of Be x Mg y AI 2(x+y) 0 4(x+y) .…”

Section: Crystallographic Setting and Refinement Of The Chrysoberyl Smentioning

confidence: 97%

“…Recent studies in different minerals indicated that the presence of specific elements at the twin boundaries play a decisive role during the twin formation (Šrot et al 2003;Daneu et al 2007bDaneu et al , 2014Drev et al 2013). The detection of twin-triggering element often presents a challenging analytical task, owing to its low amounts and difficulties of locating the nucleation core of twinned crystal where it is actually present (Rečnik and Daneu 2012).…”

Section: Atomic Structure Of (130) Chrysoberyl Twinsmentioning

confidence: 98%

Structural investigation of (130) twins and rutile precipitates in chrysoberyl crystals from Rio das Pratinhas in Bahia (Brazil)

Drev

Komelj

Mazaj

et al. 2015

American Mineralogist

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We studied V-shaped twins of chrysoberyl (BeAl 2 O 4 ) from Rio das Pratinhas pegmatites near Arataca in the Bahia state of Brazil. The local structure of the twin boundaries was determined using powder X-ray diffraction analysis (XRD), transmission electron microscopy (TEM) methods, and density functional theory (DFT) calculations. To provide the most reliable model for DFT and HRTEM simulations the structure of chrysoberyl was first refined in the orthorhombic space group 62 (Pmnb) with unit-cell parameters: a = 5.4825(1) Å, b = 9.4163(2) Å, and c = 4.4308(1) Å, with 0.5 at% of Fe 3+ present on the Al(2) sites, suggesting an average composition of BeAl 1.99 Fe 0.01 O 4 . TEM study of V-shaped twins showed that the twin boundary lies in the (130) planes, and the angle measured between the crystal domains related by mirror twin operation is ∼59.5°. Rigid structural model of (130) twin boundary in chrysoberyl was refined by DFT calculations, using a pseudo-potential method. The twin boundaries show local enrichment with Ti. Bulk chrysoberyl contains numerous nanosized TiO 2 precipitates with a distorted rutile structure, following the orientation relationship of [001] Ch {120} Ch ||[010] R {103} R . The increase of Ti at the twin boundaries and the formation of rutile-type TiO 2 precipitates in bulk chrysoberyl suggest a transient Ti-exsolution that took place after the twin formation.

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“…quartz, calcite, spinel and many others, which offer plenty of examples of morphologically prominent twinned crystals [1]. In the last decades, some investigations were carried out on artificially synthesised twins of similar compositions, with the aim to better understand conditions/driving forces necessary for twin formation, also in view of practical applications [2,3].…”

Section: Introductionmentioning

confidence: 99%

Spinel type twins of the new cubic Er₆Zn₂₃Ge compound

Solokha

Negri

Proserpio³

et al. 2015

Zeitschrift Für Kristallographie - Crystalline Materials

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The crystal structure of the new Er6Zn23Ge intermetallic compound was established by X-ray diffraction analysis on a twinned crystal (space group Fm3¯m, Wyckoff sequence: f2edba, cF120-Zr6Zn23Si, a=12.7726(6) Å). The crystal is composed of two nearly equal size domains, whose mutual orientation is described by a 180° rotation around the cubic [111] axis, i.e. a spinel-type twinning law, not common for intermetallics. Applying the nanocluster approach, Er6Ge octahedra and centered two-shell Zn45 clusters were found as structural building blocks, filling the crystal space in a NaCl-like arrangement. This description was adopted to interpret the twinning in terms of stacking faults in the fcc cubic close packed arrangement. Moreover, the assembly of the nanocluster units is proposed as a possible mechanism for crystal growth and twin formation, in agreement with the principle of the interface energy minimization. Experimental conditions such as supersaturation and co-formation of other phases are also considered as favorable factors for Er6Zn23Ge twin formation

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Twinning and epitaxial growth of taaffeite-type modulated structures in BeO-doped MgAl2O4

Cited by 17 publications

References 18 publications

Structure evolution of h.c.p./c.c.p. metal oxide interfaces in solid-state reactions

Structure evolution of h.c.p./c.c.p. metal oxide interfaces in solid-state reactions

Structural investigation of (130) twins and rutile precipitates in chrysoberyl crystals from Rio das Pratinhas in Bahia (Brazil)

Spinel type twins of the new cubic Er₆Zn₂₃Ge compound

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Twinning and epitaxial growth of taaffeite-type modulated structures in BeO-doped MgAl2O4

Cited by 17 publications

References 18 publications

Structure evolution of h.c.p./c.c.p. metal oxide interfaces in solid-state reactions

Structure evolution of h.c.p./c.c.p. metal oxide interfaces in solid-state reactions

Structural investigation of (130) twins and rutile precipitates in chrysoberyl crystals from Rio das Pratinhas in Bahia (Brazil)

Spinel type twins of the new cubic Er6Zn23Ge compound

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Product

Resources

About

Spinel type twins of the new cubic Er₆Zn₂₃Ge compound