Neutron diffraction studies of cubic tungsten bronzes

Wiseman, Philip J.; Dickens, P.G.

doi:10.1016/0022-4596(76)90206-1

Cited by 104 publications

(39 citation statements)

References 22 publications

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“…X-ray powder diffraction with a Siemens D5000 system equipped with a primary-beam monochromator and PSD detector indicated that the sample was essentially single-phase, with a pseudocubic subcell lattice constant of 3.8451(3) Å at room temperature. This equates to a sodium content of 0.74, based on the work of Brown and Banks [6], and matches the value previously reported for Na 0.73 WO 3 [5].…”

Section: Sample Preparationsupporting

confidence: 50%

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Temperature dependence of structural parameters in the perovskite Na_0.74WO₃

Darlington

Hriljac

Knight

2005

Physica Status Solidi (b)

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Na x WO 3 undergoes three phase transitions involving tilting of the oxygen octahedra about 〈100〉 pseudocubic directions. We have measured the temperature dependence of the lattice parameters between 200 and 750 K -a temperature range that spans the three transitions -and determined the evolution of the structure within each phase as temperature changes. The experiments were performed on the highresolution powder diffractometer HRPD, Rutherford Appleton Laboratory, UK, using time-of-flight neutron diffraction. The critical exponent that describes the temperature dependence of the total tilt angle has been evaluated. An unexpected change in the thermal expansion coefficient in the cubic phase is not understood: an argument based on Landau's theory of phase transitions is used to demonstrate that the change is not the result of co-existence of two phases.

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Section: Sample Preparationsupporting

confidence: 50%

“…The sample was prepared using the method of Wiseman and Dickens [5]. Appropriate quantities of anhydrous Na 2 WO 4 , WO 3 and W were ground together and placed in a gold-lined vitreous silica tube.…”

Section: Sample Preparationmentioning

confidence: 99%

Temperature dependence of structural parameters in the perovskite Na_0.74WO₃

Darlington

Hriljac

Knight

2005

Physica Status Solidi (b)

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“…Since there is no additional symmetry gained by keeping all three rotation angles equal, one might expect the a÷b-b -(10) tilt system to be (Shannon, 1976 Wiseman & Dickens (1976) Ferretti, Rogers & Goodenough (1965 more commonly observed, because it has an additional degree of freedom. In an attempt to test this assertion, POTATO was used to simulate atomic positions of a handful of known structures.…”

Section: Known Tilt Systemsmentioning

confidence: 99%

Octahedral Tilting in Perovskites. II. Structure Stabilizing Forces

Woodward¹

1997

Acta Crystallogr B Struct Sci

625

480

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The 23 Glazer tilt systems describing octahedral tilting in perovskites have been investigated. The various tilt systems have been compared in terms of their A-cation coordination and it is shown that those tilt systems in which all the A-cation sites remain crystallographically equivalent are strongly favored, when all the A sites are occupied by the same ion. Calculations based on both ionic and covalent models have been performed to compare the seven equivalent A-site tilt systems. Both methods predict that when the tilt angles become large, the orthorhombic a+b-b -tilt system will result in the lowest energy structure. This tilt system gives the lowest energy structure because it maximizes the number of short A---O interactions. The rhombohedral a-a-a-tilt system gives a structure with a slightly lower Madelung energy, but increased ion-ion repulsions destabilize this structure as the tilt angles increase. Consequently, it is stabilized by highly charged A cations and small to moderate tilt angles. The ideal cubic a°a°a° tilt system is only observed when stabilized by oversized A cations and/or M---O 7r-bonding. Tilt systems with nonequivalent A-site environments are observed when at least two A cations with different sizes and/or bonding preferences are present. In these compounds the ratio of large-to-small cations dictates the most stable tilt system.

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“…However, this rule is not true in the case of the tungsten-bronze-related phases, M x WO 3+y with M = Ca, La, and Nd, which have PTB-type structures with y = 0 at ambient pressure conditions (7)(8)(9)17), and HTB-related structures with 0 r y r 3x/2 at high pressures [1][2][3][4]18]. The former structure is denser than the latter one.…”

Section: Pressure-temperature Phase Relations and Discussionmentioning

confidence: 72%

“…The latter structures were the members n = 2, 3 and 4 of the (n)-ITB family of related phases. Previous X-ray studies of rare-earth tungsten oxide samples, prepared by conventional solid-state synthesis under ambient pressure conditions, have established that RE B0.1 WO 3 bronzes with structures of perovskite tungsten bronze (PTB) type are formed with RE = La-Lu (7)(8)(9).…”

Section: Introductionmentioning

confidence: 99%