Transformation of the Structure of ZnO–C Powders during Mechanical Activation and Spark Plasma Sintering

The processes of grinding and transformation of the structure of the ZnO–C powder mixture at the mechanical activation by ball milling in an inert atmosphere have been investigated. The mechanical activation of the ZnO–C powder mixture is shown to lead to the formation of graphene oxide shells on the surface of crushed zinc oxide particles. The influence of the duration of activation of powder mixtures on the dynamics of their compaction during spark plasma sintering and structure of the ceramics obtained has been investigated. It is established that an increase in the activation duration to 100 h leads to a monotonic decrease in the density of sintered ceramics. The carbon shell formed during sintering at ZnO grain boundaries is shown to have the structure of reduced graphene oxide.

     

Synthesis of TiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>-based ceramics by plasma spraying

Structure of ceramics obtained by the plasma spray deposition of spherical TiO₂ powders has been investigated. An electron microscopy study of the surfaces and cross sections of particles in the initial powder and of the deposited ceramic coatings was performed. X-ray diffraction and Raman scattering data proved that the coatings were mainly structured as rutile. In addition, Raman and X-ray diffraction data have revealed an amorphous phase, an anatase phase, and non-stoichiometric phases Ti₈O₁₅, Ti₁₀O₁₉, Ti₇O₁₃, etc. being present in the coatings. The observed suppression of (011) and (111) XRD peaks and an increased intensity of (110) peak are indicative of a predominant orientation of grains in the synthesized ceramics. Mechanisms of formation of the complex coating structure are discussed.     

Crystal structure of the Ca<Subscript>3</Subscript>TaGa<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>14</Subscript> compound

The absolute crystal structure of the Ca₃TaGa₃Si₂O₁₄ piezoelectric compound is refined using X-ray diffraction analysis. The unit cell parameters and final R factors are as follows: a = 8.112(1) Å, c = 4.9862(6) Å, space group P321, Z = 1, R = 0.98%, and R _w = 1.42%. It is shown that the configuration of the absolute crystal structure inherited from the seed material determines the positive sense of the optical activity of the crystal under investigation. The structural and acoustical characteristics of the Ca₃TaGa₃Si₂O₁₄ crystals are compared with those of the La₃Ga₅SiO₁₄ crystals.     

Inelastic intermolecular exchange of vibrational quanta and relaxation of vibrationally excited states in binary solid systems

The processes of molecular relaxation in the binary nitrate–perchlorate solid systems LiNO₃–LiClO₄, NaNO₃–NaClO₄, and KNO₃–KClO₄ have been investigated using Raman spectroscopy. It has been found that the relaxation time of the ν₁(A) vibration of the NO₃ ^- anion in the binary solid system is shorter than that in the pure metal nitrates. It has been shown that an increase in the relaxation rate is caused by the existence of an additional mechanism of relaxation of vibrationally excited states of the nitrate ion in the system. This mechanism is associated with the excitation of a vibration of another anion (ClO₄ ^-), as well as with the “creation” of a lattice phonon. It has been established that the condition for the realization of the relaxation mechanism is that the difference between the frequencies of the aforementioned vibrations should correspond to the range of sufficiently high densities of states of the phonon spectrum.     

On the Reasons of Assymetricity of the Shape of Contour of Vibrational Line ν1(A 1) in Raman Spectra of LiNO3 Melt

Optics and Spectroscopy - The reasons leading to the asymmetry of the shape of the ν1(А1) contour of the nitrate ion in the spectra of lithium nitrate melts were analyzed. It was shown...     

Vibrational spectra of an LiNO3–(CH3)2SO2 system

Raman and IR absorption spectra were studied and molecular relaxation characteristics of vibrations of the anion and solvent were calculated for an xLiNO₃–(1 – x)(CH₃)₂SO₂ system (x = 0.1, 0.2, 0.3, 0.4 M). It was found that it is impossible to increase the concentration of free ions involved in charge transfer in such a system by either increasing the temperature or changing the concentration composition in the studied range of x.     

Suppression of growth domains in epitaxial ZnO films on structured (0001) sapphire surface

Zinc oxide layers have been grown by magnetron sputtering in an oxygen atmosphere on structured sapphire surfaces. The formation of ZnO islands oriented in two directions (the so-called domains) was observed on (0001) Al₂O₃ surfaces with steps spaced by a distance from several thousands to several tens of thousands of nanometers. The islands formed along steps on (0001) Al₂O₃ surfaces with an ordered terrace-step structure (and, subsequently, ZnO films) have only one orientation. Another method is proposed for suppressing domains during ZnO growth on (0001) Al₂O₃ d.     

Influence of the temperature and phase state of K,Ca/NO<Subscript>3</Subscript> and K,Mg/NO<Subscript>3</Subscript> binary systems on the vibrational anharmonicity and orientational mobility of the nitrate ion

The absorption spectra of homogeneous and heterophase melts and glasses of the K,Ca/NO₃ and K,Mg/NO₃ systems are studied by IR Fourier spectroscopy. The temperature-phase dependences for the first and second order spectra are analyzed, and the anharmonicity constants for internal vibrations of the nitrate ion are estimated. The influence of finely dispersed Al₂O₃ powder on the structural-dynamic properties of the K,Ca/NO₃ and K,Mg/NO₃ systems is studied. A mechanism for charge transfer in heterophase nitrate glasses is proposed. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 176–181, March–April 2009.