Single-Crystal High-Pressure Studies of Na3ScF6

Carlson, Stefan; Xu, Yongnan; Norrestam, R.

doi:10.1006/jssc.1997.7607

Cited by 10 publications

(9 citation statements)

References 9 publications

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“…In the distorted crystal structure of iron cryolite the value ÁG 3 = 0.0011 provides evidence of the higher leading role of the complex ions. Note that in the highpressure crystal structure of scandium cryolite (Carlson et al, 1998) the cationic sublattice is less uniform than at normal pressure. This fact allows discussion on the high stability of the structure-forming sublattice of complex ions, at least up to 68.2 kbar.…”

Section: Structure Featurementioning

confidence: 99%

Structure-forming components in crystals of ternary and quaternary 3d-metal complex fluorides

Peresypkina

Блатов

2003

Acta Crystallogr Sect B

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Crystallochemical analysis and classification were performed for 139 ternary and quaternary complex fluorides with the general formula M1(n)M2(m)M3F(6), belonging to 33 structure types. Using coordination sequences and the uniformity criterion the structure-forming ionic sublattices or their combinations were found, which are responsible for the formation of stable periodic frameworks. Analysis of structure-forming motifs allows the interpretation of the crystal structures of complex fluorides as close packings of F ions with M1, M2 and M3 cations, partially occupying tetrahedral and octahedral voids, or as the packings of [M3F(6)] complex ions with M1 and M2 countercations in the voids. Cationic sublattices are noted to play an essential role, while forming crystal structures of complex fluorides. Relationships between the composition of structure-forming sublattices, the composition of compounds, and the size and charge of ions belonging to the sublattices were analysed under normal conditions, with thermal and high-pressure polymorphic transitions. Rules were formulated to predict the crystal structures of complex fluorides with a given chemical composition.

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Section: Structure Featurementioning

confidence: 99%

Structure-forming components in crystals of ternary and quaternary 3d-metal complex fluorides

Peresypkina

Блатов

2003

Acta Crystallogr Sect B

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“…Based on this understanding, we performed a similar set of calculations for the d 0 compound Na 3 ScF 6 , which also crystallizes with P 2 1 /n symmetry and for which experimental structural data under hydrostatic pressure exists. 67 We find there is no discontinuity in either the total energies ( Fig. 9) or in the evolution of the Sc-F bond lengths up to a pressure of 6.82 GPa, which indicates that no isosymmetric transitions occur up to a pressure that is approximately 4.7 GPa higher than required for the fluoromanganate.…”

Section: Discussionmentioning

confidence: 58%

Microscopic origin of pressure-induced isosymmetric transitions in fluoromanganate cryolites

Charles

Rondinelli

2014

Phys. Rev. B

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Using first-principles density functional theory calculations, we investigate the hydrostatic pressureinduced reorientation of the Mn-F Jahn-Teller bond axis in the fluoride cryolite Na3MnF6. We find a first-order isosymmetric transition occurs between crystallographically equivalent monoclinic structures at approximately 2.15 GPa, consistent with earlier experimental studies. Analogous calculations for isostructural 3d 0 Na3ScF6 show no evidence of a transition up to 6.82 GPa. Mode crystallography analyses of the pressure-dependent structures in the vicinity of the transition reveals a clear evolution of the Jahn-Teller bond distortions in cooperation with an asymmetrical stretching of the equatorial fluorine atoms in the MnF6 octahedral units. We identify a change in orbital occupancy of the eg manifold in the 3d4 Jahn-Teller active Mn(III) to be responsible for the transition, which stabilizes one monoclinic P 21/n variant over the other.

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“…Also, given the possibility for thin film growth of fluorides, [22][23][24][25] we propose a related challenge: Can polar phases be stabilized in fluoroperovskites with epitaxial strains as is achieved in oxides? [26][27][28] In this work, we use first principles calculations to examine the lattice dynamics of the cryolite Na 3 ScF 6 (P 2 1 /n) 31,32 and elpasolite K 2 NaScF 6 (F m3m). 33,34 We find that the low-frequency polar IR-active phonons in these double perovskite fluorides are dominated by the displacements of alkali metals (K and Na) with smaller accompanying displacements of the Sc 3+ ion.…”

Section: 14-16mentioning

confidence: 99%

“…31 With this in mind, we first examine the tendency to ferroelectricity by exploring the phonon frequencies of the ideal cubic phase and considering how combinations of soft modes responsible for the monoclinic symmetry support or suppress polar displacements. We find a ferroelectric lattice instability transforming as the irreducible representation (irrep) Γ − 4 (I4mm) with a frequency of 102i cm −1 .…”

Section: Computational Detailsmentioning

confidence: 99%

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Ferroelectricity ind0double perovskite fluoroscandates

Charles

Rondinelli

2015

Phys. Rev. B

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Ferroelectricity in strain-free and strained double perovskite fluorides, Na3ScF6 and K2NaScF6, is investigated using first-principles density functional theory. Although the experimental room temperature crystal structures of these fluoroscandates are centrosymmetric, i.e., Na3ScF6 (P 21/n) and K2NaScF6 (F m3m), lattice dynamical calculations reveal that soft polar instabilities exist in each prototypical cubic phases and that the modes harden as the tolerance factor approaches unity. Thus, the double fluoroperovskites bear some similarities to ABO3 perovskite oxides; however, in contrast, these fluorides exhibit large acentric displacements of alkali metal cations (Na, K) rather than polar displacements of the transition metal cations. Biaxial strain investigations of the centrosymmetric and polar Na3ScF6 and K2NaScF6 phases reveal that the paraelectric structures are favored under compressive strain whereas polar structures with in-plane electric polarizations (∼ 5-18 µC cm −2 ) are realized at sufficiently large tensile strains. The electric polarization and stability of the polar structures for both chemistries are found to be further enhanced and stabilized by a coexisting single octahedral tilt system. Our results suggest that polar double perovskite fluorides may be realized by suppression of octahedral rotations about more than one Cartesian axis; structures exhibiting in-or out-of-phase octahedral rotations about the c-axis are more susceptible to polar symmetries.

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Single-Crystal High-Pressure Studies of Na3ScF6

Cited by 10 publications

References 9 publications

Structure-forming components in crystals of ternary and quaternary 3d-metal complex fluorides

Structure-forming components in crystals of ternary and quaternary 3d-metal complex fluorides

Microscopic origin of pressure-induced isosymmetric transitions in fluoromanganate cryolites

Ferroelectricity ind0double perovskite fluoroscandates

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