Structural and calorimetric studies of mixed K2MoxW(1−x)O4 (0⩽x⩽1) compounds

Guarnieri, A.A.; Moreira, Alexandre M.; Pinheiro, Carlos B.; Speziali, Nivaldo L.

doi:10.1016/s0921-4526(03)00081-4

Cited by 8 publications

(7 citation statements)

References 11 publications

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“…[87] Use of the optimised MoÀO bond distance increases the agreement with the spectroscopic measurements. Variations of the O-Mo-O angles in the MoO 4 tetrahedra are less than 28.…”

Section: Effects Of Structural Optimisation On the Calculations Of Qumentioning

confidence: 80%

“…Herein, we present calculations of EFG and CS tensors using PAW and GIPAW methods for a set of ternary molybdates of general formula AMoO 4 , where A is a divalent cation (Ba, [81] Pb, [82] Ca, [83] Sr, [84] Cd, [85] Zn [86] ), and A' 2 MoO 4 , where A' is a monovalent cation (K, [87] Cs, [88] Rb, [89] Na, [90] NH 4 [91] ). In all these compounds, molybdenum atoms have a + VI formal oxidation state and are coordinated to four oxygen atoms in a nearly tetrahedral symmetry (see Figure 1).…”

Section: Introductionmentioning

confidence: 99%

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Density Functional Theory Calculations of ⁹⁵Mo NMR Parameters in Solid‐State Compounds

Cuny¹,

Furet²,

Gautier³

et al. 2009

ChemPhysChem

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The application of periodic density functional theory-based methods to the calculation of (95)Mo electric field gradient (EFG) and chemical shift (CS) tensors in solid-state molybdenum compounds is presented. Calculations of EFG tensors are performed using the projector augmented-wave (PAW) method. Comparison of the results with those obtained using the augmented plane wave + local orbitals (APW+lo) method and with available experimental values shows the reliability of the approach for (95)Mo EFG tensor calculation. CS tensors are calculated using the recently developed gauge-including projector augmented-wave (GIPAW) method. This work is the first application of the GIPAW method to a 4d transition-metal nucleus. The effects of ultra-soft pseudo-potential parameters, exchange-correlation functionals and structural parameters are precisely examined. Comparison with experimental results allows the validation of this computational formalism.

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“…[87] Use of the optimised MoÀO bond distance increases the agreement with the spectroscopic measurements. Variations of the O-Mo-O angles in the MoO 4 tetrahedra are less than 28.…”

Section: Effects Of Structural Optimisation On the Calculations Of Qumentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Density Functional Theory Calculations of ⁹⁵Mo NMR Parameters in Solid‐State Compounds

Cuny¹,

Furet²,

Gautier³

et al. 2009

ChemPhysChem

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show abstract

“…9,15 Several attempts to grow untwinned crystals suitable for single-crystal experiments failed so powder samples have to be used for the x-ray diffraction analysis. Due to the high hygroscopic character of the compounds the samples were handled on a nitrogen-atmosphere glove box where they were crushed into fine powders, and then placed into glass capillaries of 0.4 and 0.5 mm in diameter.…”

Section: Methodsmentioning

confidence: 99%

“…The absolute temperatures of the corresponding phase transitions were taken from differential scanning calorimetry experiments. 9,15,16 Accordingly, the temperature ranges for the modulated phase are 640͑5͒-734͑5͒ K, 601͑5͒-727͑5͒ K, and 593͑5͒-730͑5͒ K for K 2 WO 4 , K 2 Mo 0.5 W 0.5 O 4 , and K 2 MoO 4 , respectively.…”

Section: Methodsmentioning

confidence: 99%

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Modulated phase ofK2MoxW1−xO4mixed compounds using orthorhombic symmetry: A powder di

et al. 2009

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4 as exceptions among the members of AЈAЉBX 4 family because their thermotropic phase transitions do not follow the commonly observed sequence and because their modulation wave vector, unusually, lies on the pseudohexagonal plane. Until now, the modulated phases of these compounds have been interpreted using hexagonal symmetry. The present work indicates, however, that a model consisting of threefold twinned orthorhombic modulated domains better describes the satellites observed in the temperature range of 620-740 K. The Ccmm space group is proposed for the average structure of the whole family K 2 Mo x W 1−x O 4 , whereas the Ccmm͑␣00͒000 with the wave vector q = ͑0.5+ ␦͒a ‫ء‬ is the appropriate superspace group for the description of the modulated structures.The coexistence of three orthorhombic domains, each of which is rotated by 120°from each other, indeed reproduces a pseudohexagonal basis, which is a common feature in the AЈAЉBX 4 family. The usage of the twinning model allows a much simpler interpretation of the diffraction pattern and provides a more consistent way to describe the phase-transition sequence shown by the mixed K 2 Mo x W 1−x O 4 crystals.

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Fine structures and their impacts on the characteristic Raman spectra of molten binary alkali tungstates

Wang

You

et al. 2021

J Raman Spectroscopy

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Comparing with the crystalline tungstate compounds, little work has been carried out and reported on the relation among the microstructure, W–O bond lengths, and characteristic Raman‐active vibration wavenumber of the molten tungstates, which allows us to diagnose and determine the structure of unknown clusters existing in and further predict the physicochemical properties of molten binary alkali tungstates. Raman spectra of an ensemble of eight model clusters were simulated in the present work by density functional theory (DFT) to establish the effect of the fine structures and W–Onb (non‐bridging oxygen) bond lengths of W–O complexes on the characteristic wavenumber of W–Onb Raman‐active vibration modes of the molten tungstates. Results show that the characteristic wavenumbers of the symmetric stretching vibration modes of W–Onb bonds increase almost linearly with the decreasing bond length. The characteristic wavenumbers of W–Onb symmetric stretching vibration modes generally follow [WO4]2− > [WO5]4− > [WO6]6− present in the melt simultaneously. The characteristic wavenumbers were also found to increase with the number of bridging oxygen for the same W–O complex. In situ Raman spectra of molten A2WnO3n + 1 (A = Li, Na, K; n = 1, 2, 3) were then measured in order to verify the correlation observed among the microstructure, W–O bond lengths, and characteristic Raman‐active vibration mode wavenumbers. The correlation was successfully applied to deconvolute the in situ Raman spectrum of the molten Na2W3O10.

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Structural and calorimetric studies of mixed K2MoxW(1−x)O4 (0⩽x⩽1) compounds

Cited by 8 publications

References 11 publications

Density Functional Theory Calculations of ⁹⁵Mo NMR Parameters in Solid‐State Compounds

Density Functional Theory Calculations of ⁹⁵Mo NMR Parameters in Solid‐State Compounds

Modulated phase ofK2MoxW1−xO4mixed compounds using orthorhombic symmetry: A powder di

Fine structures and their impacts on the characteristic Raman spectra of molten binary alkali tungstates

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Structural and calorimetric studies of mixed K2MoxW(1−x)O4 (0⩽x⩽1) compounds

Cited by 8 publications

References 11 publications

Density Functional Theory Calculations of 95Mo NMR Parameters in Solid‐State Compounds

Density Functional Theory Calculations of 95Mo NMR Parameters in Solid‐State Compounds

Modulated phase ofK2MoxW1−xO4mixed compounds using orthorhombic symmetry: A powder di

Fine structures and their impacts on the characteristic Raman spectra of molten binary alkali tungstates

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Density Functional Theory Calculations of ⁹⁵Mo NMR Parameters in Solid‐State Compounds

Density Functional Theory Calculations of ⁹⁵Mo NMR Parameters in Solid‐State Compounds