Crystal structure of β′-Zn2V2O7

The crystal structure of the high-temperature modification of zinc pyrovanadate, namely, β′-Zn₂V₂O₇, is refined by the full-profile Rietveld method (GSAS) using the high-temperature X-ray diffraction data. The crystals are monoclinic (space group C2/m, Z = 2); the unit cell parameters are as follows: a = 6.9324(2) Å, b = 8.4394(2) Å, c = 5.0326(1) Å, and β = 108.272(2)°. Comparative analysis of the crystal structures of β′-Zn₂V₂O₇, β-Mn₂V₂O₇, and Cd₂V₂O₇ is performed.     

Statistical estimates of the influence of the source divergence angle on the characteristics of acoustic radiation transmitted through the atmosphere

The method of statistical simulation (Monte Carlo) is used for the first time to study the influence of the angular source divergence on the characteristics of transmitted acoustic radiation with allowance for the multiple scattering contribution. Results of calculations for a point source of unit power with divergence angles φ = 5, 10, 15, 20, and 25° at frequencies F = 1, 2, 3, and 4 kHz are presented for the outer scale of turbulence L ₀ = 10, 15, 20, 40, 60, and 80 m. It is established that for F = 2 kHz the multiple scattering contribution to the transmitted radiation intensity increases with the outer scale of turbulence from ∼10% (for L ₀ = 10 m) to 90% (for L ₀ = 60 m); for L ₀ = 80 m, the transmitted radiation intensity is virtually completely determined by the contribution of multiple scattering. When the width of the source directivity pattern (2φ) increases from 10 to 50°, the intensity of transmitted acoustic radiation decreases by 96%. Based on the results of statistical simulation, analytical dependences of the transmitted radiation intensity on the sound source divergence angle are suggested for typical sodar frequencies.     

Mechanism of thermal expansion of structural modifications of zinc pyrovanadate

Crystal chemical characteristics of the α and β modifications of Zn₂V₂O₇ are calculated based on in situ high-temperature X-ray measurements. The expansion of the structure is found to be strongly anisotropic up to the negative volumetric thermal expansion of the α-Zn₂V₂O₇ unit cell in the temperature range of 300–600°С, α _V =–17.94 × 10^–6 1/K. The transformations of the “hard” and “soft” sublattices with an increase temperature and at the phase transition are considered in detail. It is shown that the negative volumetric thermal expansion of α-Zn₂V₂O₇ is due to the degeneracy of the zigzag-like shape of zinc–oxygen columns at constant distances between their vertices.     

Synthesis of the Zn1.9Cu0.1SiO4 pigment via the sol–gel and coprecipitation methods

Journal of Sol-Gel Science and Technology - The Zn1.9Cu0.1SiO4 pigment was obtained by two variants of “soft” chemistry methods: using sol–gel synthesis in ethanol from TEOS and...     

Synthesis,sintering, and conductivity of Mn<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>

Studies on the sintering of manganese pyrovanadate depending on the temperature and the crystallite size show that we are prevented from obtaining a bulk ceramic sample by the anisotropic growth of grains. Investigation of the electrical properties of Mn₂V₂O₇ in the temperature range of 250–800°C reveals the activation energy at which bulk conductivity is 0.62 eV.     

Stabilizing the associated non-autonomous phase upon thermal expansion of Zn<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>

The previously unknown effect of emergence of an associated non-autonomous phase upon heating of zinc pyrovanadate Zn₂V₂O₇ within the region of negative volume expansion is detected. Comparison of the data of high-temperature X-ray diffraction of the Zn₂V₂O₇ samples synthesized via solution and solid-phase routes shows that the grain size affects the stabilization of the non-autonomous phase. The presence of a non-autonomous phase results in self-dispersion of the substance upon phase transition in heating–cooling cycles.