New Layered Oxide-Fluoride Perovskites: KNaNbOF5 and KNaMO2F4 (M = Mo6+, W6+)

Pinlac, Rachelle Ann F.; Stern, Charlotte L.; Poeppelmeier, Kenneth R.

doi:10.3390/cryst1010003

Cited by 42 publications

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“…In either case, temperature, concentration, and pH are critical factors. Crystal growth of the NCS polymorph of KNaNbOF 5 faces an additional challenge since both polymorphs of KNaNbOF 5 can be grown hydrothermally, sometimes from the same solution [11,[14][15][16][17]. Because hydrothermal crystal growth can take multiple days to weeks to obtain large single crystals, crystal growth conditions that ensure the correct polymorph crystallizes must also be targeted.…”

Section: Introductionmentioning

confidence: 99%

Hydrothermal crystal growth, piezoelectricity, and triboluminescence of KNaNbOF5

Chang

Edwards

Frazer

et al. 2016

Journal of Solid State Chemistry

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Section: Introductionmentioning

confidence: 99%

Hydrothermal crystal growth, piezoelectricity, and triboluminescence of KNaNbOF5

Chang

Edwards

Frazer

et al. 2016

Journal of Solid State Chemistry

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“…Knowledge of factors that can yield polar structures and align dipoles is important when attempting to synthesize new SHG materials. The KNaNbOF 5 system is appealing for study, since both centrosymmetric (CS) 7 and polar NCS polymorphs 8 are known. This allows for direct comparison, since the identities of the cations are the same.…”

Section: ■ Introductionmentioning

confidence: 99%

How Lewis Acidity of the Cationic Framework Affects KNaNbOF₅ Polymorphism

et al. 2014

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The valence matching principle is used to explain the loss of inversion symmetry in the noncentrosymmetric (NCS) polymorph of KNaNbOF5 in comparison to its centrosymmetric (CS) polymorph. The [NbOF5](2-) anion has five contacts to both potassium and sodium in the NCS polymorph, whereas in the CS polymorph there are only four contacts to potassium and six contacts to sodium. The lower average Lewis acidity of the cationic framework in the NCS polymorph relative to the CS polymorph reflects the loss of inversion symmetry. This lower average Lewis acidity is achieved during hydrothermal synthesis with a potassium-rich solution when the K:Na ratio in the reaction is greater than 1:1, as the Lewis acidity of potassium is lower than that of sodium. The contrasting coordination environments are manifested in secondary distortions that weaken the primary Nb═O interaction and lengthen the Nb═O bond in the NCS polymorph. An unusual heat-induced phase transition from the CS to the NCS polymorph was studied with in situ powder X-ray diffraction. The transition to the NCS polymorph upon cooling occurs through an intermediate phase(s).

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“…While much of the focus thus far has been on simple perovskites, a survey of the inorganic crystal structure database (https://icsd.fiz-karlsruhe.de/) reveals that of the nearly 55,000 complex oxides listed today, >99% are layered structures; surprisingly, only ∼2% of these compounds have been explored. However, recent advances in unit-cell level control in the epitaxial growth of thin films and heterostructures are opening up large families of layered oxide topologies in thin film form, such as the A 2 A ′ n −1 B n O 3 n +1 Ruddlesden–Popper (RP), AA ′ n −1 B n O 3 n +1 Dion–Jacobson, (Bi 2 O 2 )( A n −1 B n O 3 n +1 ) Aurivillius and ( AB O 3 ) m /( A′B′ O 3 ) n perovskite superlattices678910111213141516171819202122232425. The layer dimensions (subscripts m and n ) of these materials along with strain and chemical ordering can be tuned to modify or activate new phenomena, such as ferroelectricity2627, colossal-magnetoresistance2829, ferromagnetism3031, multiferroicity32, superconductivity33 and ionic conductivity34.…”

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Atomic scale imaging of competing polar states in a Ruddlesden–Popper layered oxide

et al. 2016

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Layered complex oxides offer an unusually rich materials platform for emergent phenomena through many built-in design knobs such as varied topologies, chemical ordering schemes and geometric tuning of the structure. A multitude of polar phases are predicted to compete in Ruddlesden–Popper (RP), An+1BnO3n+1, thin films by tuning layer dimension (n) and strain; however, direct atomic-scale evidence for such competing states is currently absent. Using aberration-corrected scanning transmission electron microscopy with sub-Ångstrom resolution in Srn+1TinO3n+1 thin films, we demonstrate the coexistence of antiferroelectric, ferroelectric and new ordered and low-symmetry phases. We also directly image the atomic rumpling of the rock salt layer, a critical feature in RP structures that is responsible for the competing phases; exceptional quantitative agreement between electron microscopy and density functional theory is demonstrated. The study shows that layered topologies can enable multifunctionality through highly competitive phases exhibiting diverse phenomena in a single structure.

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New Layered Oxide-Fluoride Perovskites: KNaNbOF5 and KNaMO2F4 (M = Mo6+, W6+)

Cited by 42 publications

References 33 publications

Hydrothermal crystal growth, piezoelectricity, and triboluminescence of KNaNbOF5

Hydrothermal crystal growth, piezoelectricity, and triboluminescence of KNaNbOF5

How Lewis Acidity of the Cationic Framework Affects KNaNbOF₅ Polymorphism

Atomic scale imaging of competing polar states in a Ruddlesden–Popper layered oxide

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New Layered Oxide-Fluoride Perovskites: KNaNbOF5 and KNaMO2F4 (M = Mo6+, W6+)

Cited by 42 publications

References 33 publications

Hydrothermal crystal growth, piezoelectricity, and triboluminescence of KNaNbOF5

Hydrothermal crystal growth, piezoelectricity, and triboluminescence of KNaNbOF5

How Lewis Acidity of the Cationic Framework Affects KNaNbOF5 Polymorphism

Atomic scale imaging of competing polar states in a Ruddlesden–Popper layered oxide

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How Lewis Acidity of the Cationic Framework Affects KNaNbOF₅ Polymorphism