Studies of phases in the KNbO3Nb2O5 system by high-resolution electron microscopy and X-ray powder diffraction

Lundberg, Monica; Sundberg, Margareta

doi:10.1016/0022-4596(86)90172-6

Cited by 40 publications

(31 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[3][4][5] A lead-free analogue to PN is strontium barium niobate, Sr x Ba 1-x Nb 2 O 6 or SBN, which is apparently stable in the TTB structure down to ambient temperature, although with a lower T C of 70-200 • C, depending on composition. 6,7 Both PN and SBN have the general formula (A1) 2 (A2) 4 C 4 (B1) 2 (B2) 8 O 30 , with five formula units in the unit cell, and space group symmetry P4/mbm in the aristotype structure. The A1 and A2 sites form, respectively, pentagonal and square channels that run parallel to the tetragonal axis, and which accomodate the Pb 2+ , Sr 2+ and Ba 2+ cations.…”

Section: Introductionmentioning

confidence: 99%

“…The C sites form narrow triangular channels, and are usually vacant, as only a few cations such as Li + and Nb 5+ are small enough for these sites. 8,9 The B1 and B2 sites are symmetrically different While PN and SBN are similar in terms of structure, there are fundamental differences in the behaviour of the two compounds. PN is a classical ferroelectric, while SBN is ferroelectric for barium-rich compositions, but becomes relaxor-like for strontium contents higher than approximately x = 0.6.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

On the energetics of cation ordering in tungsten-bronze-type oxides

Olsen

Selbach

Grande

2015

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

Oxides with the tetragonal tungsten bronze (TTB) structure are well-known ferroelectrics that show a large flexibility both with respect to chemical composition and cation ordering. Two of the simplest compounds in this family are lead metaniobate (PbNb 2 O 6 or PN) and strontium barium niobate (Sr x Ba 1-x Nb 2 O 6 or SBN). While PN is a classical ferroelectric, SBN goes from ferroelectric to relaxor-like with increasing Sr content, with a polar direction different from that in PN. The partially occupied sublattices in both systems give the possibility for cation order-disorder phenomena, but it is not known if or how this influences the polarization and ferroelectricity. Here, we use density functional theory (DFT) calculations to investigate how cation and cation vacancy ordering influences the energetics of these compounds, by comparing both the energy differences and the barriers for transition between different cation configurations. We extend the thermodynamic model of O'Neill and Navrotsky, originally developed for cation interchange in spinels, to describe the order-disorder phenomenology in TTB oxides. The influence of order-disorder processes on the functional properties of PN and SBN is discussed.

show abstract

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

On the energetics of cation ordering in tungsten-bronze-type oxides

Olsen

Selbach

Grande

2015

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

show abstract

“…l(d), it is apparent that other phases with related structures might be formed. For example, structures built up of rows of six or eight cornersharing MO6 octahedra, instead of seven, can be temperature (Gasperin, 1982) and a tetragonal tungsten-bronze-related structure at high temperature (Lundberg & Sundberg, 1986). The reason why the KNb308 phase prefers to adopt these two structure types instead of the shear structure might be answered by lattice-energy-minimization calculations.…”

Section: Resultsmentioning

confidence: 99%

“…The preparation of the electron-microscopy samples has previously been described (Lundberg & Sundberg, 1986). The specimens were examined in a JEOL 200CX electron microscope equipped with an ultra-high-resolution top-entry goniometer stage with tilt angles of +10 °.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Studies of K₃Nb₇O₁₉ by high-resolution electron microscopy and X-ray powder diffraction

Sundberg¹,

Lundberg²

1987

Acta Crystallogr Sect B

View full text Add to dashboard Cite

An idealized structure model of the K3Nb7Ol9 compound has been deduced from high-resolution electron micrographs. For simplicity the structure was derived in a pseudo-monoclinic system with triclinic symmetry (space group P1) and unit-cell dimensions a = 13.777 (2), b =6-431 (1), c= 18.897 (6) A, a-~ 90, /3 = 98.06 (2) and y -~ 90 °, V = 1657.7 A 3, Z = 4. It has been verified both by simulated image calculations in two projections and by X-ray powder diffraction studies. The structure consists of a threedimensional framework which is built up of pairs of NbO6 octahedra having one edge in common in such a way that the structure can be described by means of{011} crystallographic shear in the ReO3 type structure. The pairs are linked by edge and corner sharing as in the {120} crystallographic-shear (CS) structure M702o. Two kinds of tunnels are formed, in which the K atoms are located. The structure thus independently derived agrees with that recently published by triclinic. We have refined the cell parameters given in that article: a = 14.1282 (9), b--9.9369 (9), c = 6.4553 (6) A, a= 106.44(1), /3=95.856(6) and y= 97.30 (1) °, V= 853.05 ~3, Z =2, M~ = 1071.64, and Dx = 4.17 g cm -3. However, in this paper the structure is described in a different manner and discussed in relation to neighbouring compounds of this system.

show abstract

Potassium Tantalate K₆Ta_10.8O₃₀ with Tungsten Bronze Structure and Its Photocatalytic Property

Wang

Xiao

et al. 2017

Chin. J. Chem.

View full text Add to dashboard Cite

With the tunable and flexible physicochemical properties, tantalate photocatalysts with tungsten bronze structure are worth being studied. In this work, we successfully synthesized a novel potassium tantalate K6Ta10.8O30 with tungsten bronze structure using a facile solid‐state reaction route. The effects of calcination time on the phase composition, morphology and crystallinity of the obtained samples were studied by XRD and SEM analyses. In addition, the photocatalytic activity of the samples was evaluated by the degradation of ARG dye under UV light irradiation. The results indicated that the K6Ta10.8O30 showed high photocatalytic activity for degradation of ARG and the photocatalytic degradation of ARG followed the first order kinetics. Furthermore, the possible photocatalytic mechanism of the K6Ta10.8O30 photocatalyst was proposed based on tungsten bronze structure feature and the scavengers experimental results. This study would give a new insight into tantalate photocatalysts.

show abstract

Studies of phases in the KNbO3Nb2O5 system by high-resolution electron microscopy and X-ray powder diffraction

Cited by 40 publications

References 14 publications

On the energetics of cation ordering in tungsten-bronze-type oxides

On the energetics of cation ordering in tungsten-bronze-type oxides

Studies of K₃Nb₇O₁₉ by high-resolution electron microscopy and X-ray powder diffraction

Potassium Tantalate K₆Ta_10.8O₃₀ with Tungsten Bronze Structure and Its Photocatalytic Property

Contact Info

Product

Resources

About

Studies of phases in the KNbO3Nb2O5 system by high-resolution electron microscopy and X-ray powder diffraction

Cited by 40 publications

References 14 publications

On the energetics of cation ordering in tungsten-bronze-type oxides

On the energetics of cation ordering in tungsten-bronze-type oxides

Studies of K3Nb7O19 by high-resolution electron microscopy and X-ray powder diffraction

Potassium Tantalate K6Ta10.8O30 with Tungsten Bronze Structure and Its Photocatalytic Property

Contact Info

Product

Resources

About

Studies of K₃Nb₇O₁₉ by high-resolution electron microscopy and X-ray powder diffraction

Potassium Tantalate K₆Ta_10.8O₃₀ with Tungsten Bronze Structure and Its Photocatalytic Property