Some characteristics of niobates having “filled” tetragonal tungsten bronze-like structures

Uitert, L. G. Van; Levinstein, H. J.; Rubin, J. J.; Capio, C. D.; Dearborn, E. F.; Bonner, William A.

doi:10.1016/0025-5408(68)90024-x

Cited by 145 publications

(31 citation statements)

References 14 publications

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“…TTBs consist of layers of distorted B1O 6 and B2O 6 octahedra sharing corners so that they form three different interstices: pentagonal (A2); square (A1, sometimes referred to as the perovskite site) and trigonal (C) which may be occupied by cations according to a general formula (A2) 4 (A1) 2 (C) 4 (B1) 2 (B2) 8 O 30 , Figure 1. 2 For so-called 'stuffed' TTBs, such as K 6 Li 4 Nb 10 O 30 (KLN), Li is found in the trigonal C site 3 but in 'filled' TTBs the trigonal interstice C is empty and the general formula reverts to (A2) 4 (A1) 2 (B1) 2 (B2) 8 3 For 'unfilled' TTBs, such as Sr x Ba 1-x Nb 2 O 6 , some of the A1/A2 sites remain vacant. 4 Several studies have attempted to classify TTBs using a geometric tolerance-factor (t) approach similar to that defined for perovskites by Goldschmidt 5 .…”

Section: ) Introductionmentioning

confidence: 99%

A Crystal-Chemical Framework for Relaxor versus Normal Ferroelectric Behavior in Tetragonal Tungsten Bronzes

et al. 2015

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Tetragonal tungsten bronzes (TTBs), an important class of oxides known to exhibit ferroelectricity, undergo complex distortions, including rotations of oxygen octahedra, which give rise to either incommensurately or commensurately modulated superstructures. Many TTBs display broad, frequency-dependent relaxor dielectric behavior rather than sharper frequency-independent normal ferroelectric anomalies, but the exact reasons that favor a particular type of dielectric response for a given composition remain unclear. In this contribution the influence of incommensurate/commensurate displacive modulations on the onset of relaxor/ferroelectric behavior in TTBs is assessed in the context of basic crystal-chemical factors, such as positional disorder, ionic radii and polarizabilities, and point defects. We present a predictive crystal-chemical model that rationalizes composition–structure–properties relations for a broad range of TTB systems.

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Section: ) Introductionmentioning

confidence: 99%

A Crystal-Chemical Framework for Relaxor versus Normal Ferroelectric Behavior in Tetragonal Tungsten Bronzes

et al. 2015

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“…These materials, known to exhibit diverse properties as a result of compositional flexibility and by a higher probability for cation ordering, may offer better ways of attaining room-temperature ferroelectricity and (anti)ferromagnetism, multiferroic behaviour and eventually magnetoelectric coupling [2,8]. Whilst ferroelectric TTBs (including Ba 2 NaNb 5 O 15 [9][10][11] and (Ba,Sr)Nb 2 O 6 [12][13][14]) were widely investigated during the 1960s and 1970s, our understanding of manipulating this structure type is still poor, with the research surprisingly limited compared to that in perovskites [5]. Early attempts focused on tungsten bronzes of nominal composition A 6 B 10 O 30 (mainly compositions where the C-sites are vacant).…”

Section: Introductionmentioning

confidence: 99%

Elastic and anelastic relaxations accompanying relaxor ferroelectric behaviour of Ba6GaNb9O30 tetragonal tungsten bronze from resonant ultrasound spectroscopy

Rotaru

Schiemer

Carpenter

2016

J Therm Anal Calorim

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Tetragonal tungsten bronze (TTB) structures offer some promise as lead-free ferroelectrics and have an advantage of great flexibility in terms of accessible composition ranges due to the number of crystallographic sites available for chemical substitution. The ferroic properties of interest are coupled with strain, which will be important in the context of stability, switching dynamics and thin film properties. Coupling of strain with the ferroelectric order parameter gives rise to changes in elastic properties, and these have been investigated for a ceramic sample of Ba 6 GaNb 9 O 30 (BGNO) by resonant ultrasound spectroscopy. Room temperature values of the shear and bulk moduli for BGNO are rather higher than for TTBs with related composition which are orthorhombic at room temperature, consistent with suppression of the ferroelectric transition. Instead, a broad, rounded minimum in the shear modulus measured at *1 MHz is accompanied by a broad rounded maximum in acoustic loss near 115 K and signifies relaxor freezing behaviour. Elastic softening with falling temperature from room temperature, ahead of the freezing interval, is attributed to the development of dynamical polar nanoregions (PNRs), whilst the nonlinear stiffening below *115 K is consistent with a spectrum of relaxation times for freezing of the PNR microstructure.

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“…in K 6 Li 4 Nb 10 O 30 [13]; 'filled' compositions have fully occupied A-and B-sites but the C-site is vacant, e.g. in Ba 2 NaNb 5 O 15 [14][15][16]; finally, 'unfilled' compositions exist where the A-site is only partly occupied (typically 5/6). The latter category includes the first reported ferroelectric TTB oxides PbNb 2 O 6 and (Sr,Ba)Nb 2 O 6 [17][18][19][20]; the other examples cited above are also ferroelectric.…”

Section: Introductionmentioning

confidence: 99%

Towards novel multiferroic and magnetoelectric materials: dipole stability in tetragonal tungsten bronzes

Rotaru

Miller

Arnold

et al. 2014

Phil. Trans. R. Soc. A.

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We discuss the strategy for development of novel functional materials with the tetragonal tungsten bronze structure. From the starting composition Ba 6 GaNb 9 O 30 , the effect of A- and B-site substitutions on the dielectric properties is used to develop an understanding of the origin and stability of the dipolar response in these compounds. Both tetragonal strain induced by large B-site cations and local strain variations created by isovalent A-site substitutions enhance dipole stability but result in a dilute, weakly correlated dipolar response and canonical relaxor behaviour. Decreasing cation size at the perovskite A2-site increases the dipolar displacements in the surrounding octahedra, but insufficiently to result in dipole ordering. Mechanisms introducing small A-site lanthanide cations and incorporation of A-site vacancies to induce ferroelectricity and magnetism are presented.

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Some characteristics of niobates having “filled” tetragonal tungsten bronze-like structures

Cited by 145 publications

References 14 publications

A Crystal-Chemical Framework for Relaxor versus Normal Ferroelectric Behavior in Tetragonal Tungsten Bronzes

A Crystal-Chemical Framework for Relaxor versus Normal Ferroelectric Behavior in Tetragonal Tungsten Bronzes

Elastic and anelastic relaxations accompanying relaxor ferroelectric behaviour of Ba6GaNb9O30 tetragonal tungsten bronze from resonant ultrasound spectroscopy

Towards novel multiferroic and magnetoelectric materials: dipole stability in tetragonal tungsten bronzes

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