Perovskite-like K₃TiOF₅ Exhibits (3 + 1)-Dimensional Commensurate Structure Induced by Octahedrally Coordinated Potassium Ions

Abstract

Elpasolite-and cryolite-type oxyfluorides can be regarded as superstructures of perovskite and exhibit structural diversity. While maintaining a similar structural topology with the prototype structures, changes in the size, electronegativity, and charge of cation and/or anion inevitably lead to structural evolution. Therefore, the nominal one-toone relation suggested by a doubled formula of perovskite does not guarantee a simple 2-fold superstructure for many cases. Herein, the commensurately modulated perovskite-like K 3 TiOF 5 was refined at 100 K from single-crystal X-ray diffraction data by using a pseudotetragonal subcell with lattice parameters of a = b = 6.066(2) Å and c = 8.628(2) Å. The length of the modulation vector was refined to 0.3a* + 0.1b* + 0.25c*. In the commensurate supercell of K 3 TiOF 5 , the B-site Ti 4+ and K + cations in [TiOF 5 ] 3− and [KOF 5 ] 6− octahedral units were found to be significantly displaced from the average atomic positions refined in the subcell. The displacements of the K + cations are ±0.76 Å, and those for the Ti 4+ cations are approximately ±0.13 Å. One-and two-dimensional solid-state 19 F NMR measurements revealed two tightly clustered groups of resonances in a ratio of ca. 4:1, assigned to equatorial and axial fluorine, respectively, consistent with local [TiOF 5 ] 3− units. S/TEM results confirmed the average structure. Electronic structure calculations of the idealized I4mm subcell indicate the instability to a modulated structure arises from soft optical modes that is controlled by the octahedrally coordinated B-site potassium ions in the cryolite-type structure.

Isoreticular Design of KTiOPO4-Like Deep-Ultraviolet Transparent Materials Exhibiting Strong Second-Harmonic Generation

“…The Δd for the [ZrO 2 F 6 ] and [HfO 2 F 6 ] polyhedra are 4.06 × 10 −4 and 3.41 × 10 −4 , respectively. The bandgap is inversely related to the magnitude of distortion of the d 0 -TM polyhedra in the ZOF/HOF and d 0 -TM oxyfluoride systems39,40,49,50,52,56 (Figure2c); the decrease in distortion with [ZrO 2 F 6 ] and [HfO 2 F 6 ] leads to an increase in the bandgap. These studies with high coordination number Zr 4+ /Hf 4+ -centered polyhedra confirm the feasibility of increasing the bandgap of d 0 -TM polyhedra by reducing the extent of distortion.To elucidate the origin of the wide bandgaps of ZOF and HOF, first-principles calculations were performed with density functional theory using the CASTEP package.…”

Mechanochemical Fabrication of a Mn4+-Activated Inorganic Rb2KTiOF5 Perovskite Red Phosphor for White Light-Emitting Diodes

“…The refined results show excellent agreement with the published crystal structure. 34,35 Meanwhile, six equal Mn−O/F bonds (∼1.883 Å in length) formed an octahedral [Mn(O/F) 6 ] moiety. The morphologies of the asprepared Rb 2 KTiOF 5 :Mn 4+ were characterized by scanning electron microscopy, transmission electron microscopy (TEM), and high-angle annular dark field imaging (HAADF) (Figure 2 and Figure S1c).…”

The Crystal Structure of BaZn2Se2(OH)2 Featuring Brownmillerite‐Type Layers

“…Heteroanionic materials refer to inorganic compounds containing more than one type of anion or multiple anionic groups. [1,2] Compared to homoanionic materials, heteroanionic materials are able to create versatile coordination geometries through inserting coordinating anions with different sizes, charge, polarity and electronegativity; [3][4][5][6][7] further, the basic building units can either be homoleptic or heteroleptic polyhedra, in which each cation is bonded to a single type of anion or more than one type of anion, respectively. [8] Oxychalcogenides are a well-studied class of heteroanionic materials, which combine both oxide (O 2À ) and chalcogenide ions (Q = S 2À , Se 2À , or Te 2À ), desired for exploring new materials with collective physical properties, e. g. magnetism, [4,9] superconductivity, [10] and thermoelectrics.…”

“…Heteroanionic materials refer to inorganic compounds containing more than one type of anion or multiple anionic groups [1,2] . Compared to homoanionic materials, heteroanionic materials are able to create versatile coordination geometries through inserting coordinating anions with different sizes, charge, polarity and electronegativity; [3–7] further, the basic building units can either be homoleptic or heteroleptic polyhedra, in which each cation is bonded to a single type of anion or more than one type of anion, respectively [8] …”