Journal ArticleDOI
Negative Thermal Expansion in ZrW2O8 and HfW2O8
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TLDR
In this article, the authors used high-resolution neutron powder diffraction data taken at 14 temperatures from 0.3 to 693 K to study the structural properties of ZrW2O8 and HfW2Os8.Abstract:
Isostructural ZrW2O8 and HfW2O8 show strong negative thermal expansion from 0.3 K up to their decomposition temperatures of approximately 1050 K. This behavior is especially unusual because these compounds are apparently cubic over their entire existence range. Detailed structural studies of ZrW2O8 were conducted using high-resolution neutron powder diffraction data taken at 14 temperatures from 0.3 to 693 K. Below 428 K, ZrW2O8 adopts the acentric space group P213 and has a well-ordered structure containing corner-sharing ZrO6 octahedra and two crystallographically distinct WO4 tetrahedra. Above the phase transition at 428 K, which appears to be second order, the space group becomes centric Pa3. The structure is now disordered with one oxygen site 50% occupied, suggesting the possibility of high oxygen mobility. Oxygen motion above 428 K is also suggested by dielectric and ac impedance measurements. The negative thermal expansion of ZrW2O8 and HfW2O8 is related to transverse thermal vibrations of bridgi...read more
Citations
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Whole powder pattern decomposition methods and applications: A retrospection
TL;DR: The genesis of the modern whole powder pattern decomposition methods (the so-called Pawley and Le Bail methods) is detailed and their importance and domains of application are decoded from the most cited papers citing them.
Journal ArticleDOI
Negative thermal expansion
TL;DR: In this article, the underlying thermodynamics, emphasizing the roles of thermal stress and elasticity, are reviewed, and vibrational and non-vibrational mechanisms operating on the atomic scale that are responsible for negative expansion in a wide range of materials.
Journal ArticleDOI
Negative Thermal Expansion in a Large Molybdate and Tungstate Family
TL;DR: Negative thermal expansion has been discovered in a very large family of oxides represented by the formula A{sub 2}M{sub 3}O{sub 12} where the A and M cations are coordinated by oxygen octahedrally and tetrahedraally, respectively as discussed by the authors.
Journal ArticleDOI
Compressibility, Phase Transitions, and Oxygen Migration in Zirconium Tungstate, ZrW2O8
TL;DR: In situ neutron diffraction experiments show that at pressures above 2 kilobars, cubic zirconium tungstate (ZrW2O8) undergoes a quenchable phase transition to an orthorhombic phase, the structure of which has been solved from powder diffraction data.
Journal ArticleDOI
Negative thermal expansion in Sc2(WO4)3
TL;DR: Rietveld refinement as a function of temperature suggests that the intrinsic negative thermal expansion can be related to transverse vibrations of bridging oxygen atoms in the structure, which leads to coupled tilting of the quasi-rigid framework polyhedra and causes the structure to become more dense with increasing temperature.
References
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Journal ArticleDOI
SIRPOW.92 – a program for automatic solution of crystal structures by direct methods optimized for powder data
Angela Altomare,Giovanni Luca Cascarano,C. Giacovazzo,Antonietta Guagliardi,Maria Cristina Burla,Giampiero Polidori,Mercedes Camalli +6 more
Journal ArticleDOI
Bond-valence parameters for solids
N. E. Brese,Michael O'Keeffe +1 more
TL;DR: In this article, it is shown that there is a strong linear correlation between the parameters for bonds from cations to pairs of anions, and this correlation is used to develop an interpolation scheme that allows the estimation of bond-valence parameters for 969 pairs of atoms.
Journal ArticleDOI
Ab-initio structure determination of LiSbWO6 by X-ray powder diffraction
TL;DR: In this article, the crystal structure of LiSbWO6 was solved from X-ray powder diffraction data and the structure was refined using Rietveld profile refinement principles.
Journal ArticleDOI
Empirical bond-strength–bond-length curves for oxides
I. D. Brown,R. D. Shannon +1 more
TL;DR: In this article, it was shown that all ions with an isoelectronic core can be fitted by a single pair of parameters, R0 and N, that are independent of the ionic character of the bond and the coordination number of the cation.
Journal ArticleDOI
Infrared and Raman study of WO3 tungsten trioxides and WO3, xH2O tungsten trioxide tydrates
TL;DR: In this article, the infrared and Raman spectra of powder samples of WO3 (monoclinic and hexagonal) and XH 2 O (x = 1,2, 1 3 ) have been recorded and the most characteristic vibrations are discussed with reference to the available structural data.