Thermally induced reversible phase transformations of boroleucite, KBSi2O6

Krzhizhanovskaya, Maria G.; Бубнова, Р. С.; Derkacheva, E. S.; Depmeier, Wulf; Филатов, С. К.

doi:10.1127/ejm/2015/0027-2505

Cited by 4 publications

(2 citation statements)

References 16 publications

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“…Lowering of symmetry followed by its increasing is rare in phase transitions. An example of such phase transitions is known in KBSi 2 O 6 : I43d $ P2 1 /a $ Ia3d (Krzhizhanovskaya et al, 2016).…”

Section: Resultsmentioning

confidence: 99%

Orientational order-disorder γ ↔ β ↔ α′ ↔ α phase transitions in Sr₂B₂O₅ pyroborate and crystal structures of β and α phases

Волков

Dušek

Бубнова

et al. 2017

Acta Crystallogr Sect B

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Crystal structures of -,and -Sr 2 B 2 O 5 polymorphs resulting from the $ (at 565 K) $ (at 637 K) 0 $ (at 651 K) sequence of reversible first-order phase transitions are studied by high-temperature single-crystal X-ray diffraction, high-temperature X-ray powder diffraction, differential scanning calorimetry and impedance spectroscopy. Out of these phases, the structure of -Sr 2 B 2 O 5 was already known whereas the structures ofand -Sr 2 B 2 O 5 were determined for the first time. The sequence of phase transitions is associated with an unusual change of symmetry, with triclinic intermediate -Sr 2 B 2 O 5 phase and monoclinic low-temperature -Sr 2 B 2 O 5 as well as high-temperature -Sr 2 B 2 O 5 phase. Taking the -Sr 2 B 2 O 5 phase with space group P2 1 /c as a parent structure, the -Sr 2 B 2 O 5 phase was refined as a twofold superstructure with symmetry P2 1 /c, whereas the -Sr 2 B 2 O 5 phase was a sixfold superstructure with symmetry P1. To construct a unified structure model for all Sr 2 B 2 O 5 modifications, phases ofand -Sr 2 B 2 O 5 were also refined as commensurately modulated structures using the basic unit cell of the parent -Sr 2 B 2 O 5 . The phase transitions are related to the orientational order-disorder arrangement of B 2 O 5 pyroborate groups, where the degree of disorder grows towards the hightemperature phase. Thermal expansion is strongly anisotropic and dictated by preferable orientations of BO 3 triangles in the structure. The intermediate phase 0 -Sr 2 B 2 O 5 , stable over a narrow temperature range (637-651 K), features the largest anisotropy of expansion for the known borates: 11 = 205, 22 = 57, 33 = À81 Â 10 À6 K À1 .

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Section: Resultsmentioning

confidence: 99%

Orientational order-disorder γ ↔ β ↔ α′ ↔ α phase transitions in Sr₂B₂O₅ pyroborate and crystal structures of β and α phases

Волков

Dušek

Бубнова

et al. 2017

Acta Crystallogr Sect B

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“…Встречаются исключения из этой тенденции, например сера S, 95 °С: ромбическая -моноклинная модификации. Недавно обнаружены также превращения боросиликатов (Krzhizhanovskaya et al, 2016(Krzhizhanovskaya et al, , 2018(Krzhizhanovskaya et al, , 2019, протекающие с понижением симметрии при нагревании: Ca 2 B 2 SiO 7 , тетрагональная-ромбическая; KBSi 2 O 6 , кубическая-моноклинная; причем оба эти превращения обратимы.…”

Section: зависимость симметрии вещества от температурыunclassified

Symmetry statistics of mineral species in various thermodynamic conditions

Филатов

Константинович²

2019

Zapiski RMO

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Powder X-Ray Diffraction Data on Polymorphism of RbBSi2O6 and Crystal Structure of Its High-Temperature Modification

2018

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Thermally induced reversible phase transformations of boroleucite, KBSi2O6

Cited by 4 publications

References 16 publications

Orientational order-disorder γ ↔ β ↔ α′ ↔ α phase transitions in Sr₂B₂O₅ pyroborate and crystal structures of β and α phases

Orientational order-disorder γ ↔ β ↔ α′ ↔ α phase transitions in Sr₂B₂O₅ pyroborate and crystal structures of β and α phases

Symmetry statistics of mineral species in various thermodynamic conditions

Powder X-Ray Diffraction Data on Polymorphism of RbBSi2O6 and Crystal Structure of Its High-Temperature Modification

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Thermally induced reversible phase transformations of boroleucite, KBSi2O6

Cited by 4 publications

References 16 publications

Orientational order-disorder γ ↔ β ↔ α′ ↔ α phase transitions in Sr2B2O5 pyroborate and crystal structures of β and α phases

Orientational order-disorder γ ↔ β ↔ α′ ↔ α phase transitions in Sr2B2O5 pyroborate and crystal structures of β and α phases

Symmetry statistics of mineral species in various thermodynamic conditions

Powder X-Ray Diffraction Data on Polymorphism of RbBSi2O6 and Crystal Structure of Its High-Temperature Modification

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Product

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Orientational order-disorder γ ↔ β ↔ α′ ↔ α phase transitions in Sr₂B₂O₅ pyroborate and crystal structures of β and α phases

Orientational order-disorder γ ↔ β ↔ α′ ↔ α phase transitions in Sr₂B₂O₅ pyroborate and crystal structures of β and α phases