Preparation and characterisation of ceramic and thin film Zn(_2)SnO(_4)

Ceramic zinc stannate, Zn(_2)SnO(_4), was prepared from 1SnO(_2):2ZnO mixture using powders of the highest commercially available purity. The solid state reaction between the ZnO and the SnO(_2), thought to be an evaporation-recondensation mechanism, was found to start at ~ 900 ˚C (12 hours heating, rate 5 ˚C min(^-1)). However, the reaction did not go to completion in the timescale of the experiment unless the temperature was raised to~1300 C. In this case mono-phase, polycrystalline Zn(_2)SnO(_4) was produced, as confirmed by X-ray diffraction (XRD), scanning electron microscopy and energy dispersive X-ray analysis (EDAX). Further evidence for these reaction temperatures was obtained from thermal analysis experiments. As-sintered, Zn(_2)SnO(_4) was insulating (σ — 10(^19) Ω(^-1) cm(^-1)) although it could be made conductive, by a reduction heat-treatment. This entailed refiring the sintered pellets of Zn(_2)SnO(_4) in an atmosphere of mixture gas (25% H(_2) + 75% N(_2)) at ~ 450 ˚C for 14 hours (heating rate of 10 C min(^-1)). This reduced the conductivity to values of σ~1 x 10(^-2) Ω(^-1) cm(^-1) . XRD failed to reveal any changes in the phase of the material after the reduction treatment. Several dopants were investigated, the most successful of which was in, using a vapour phase method. Doping with In this way gave a significant change in the colour from white to dark grey together with a reduction in electrical resistivity, without recourse to further heating treatments. No change in the usual phase of the Zn(_2)SnO(_4) was detected. Doping with group V oxides, such as Nb(_2)O(_5), V(_2)O(_5) etc, produced changes in the colour from white to dark grey, but no reduction in the resistivity, unless further heating treatments were carried out in reducing ambients. When high concentrations of Nb were introduced an additional phase, possibly Nb(_2)Sn(_2)O(_7) was observed by XRD. Thin film Zn(_2)SnO(_4) was prepared by Electron Beam Evaporation using Zn2Sn04 sintered powder as the evaporant material. The thin films were deposited onto glass substrates, at a range of substrate temperatures between room temperature and 250 ˚C. XRD was used to confirm the formation of Zn(_2)SnO(_4), and provide estimates for the grain size, which varied from 20 to 25 nm. RHEED studies indicated that the grain size increased as the substrate temperature was increased. SEM revealed that the thin films were flat and uniform, with no cracks. The optical transmission of the thin films was about 88% for films deposited at 200 ˚C, but decreased significantly as the substrate temperature was decreased. The spectral dependence of complex refractive index (n&k) suggested that true thin film formation did not take place until the substrate temperature exceeded ~ 150 ˚C, and that the material was apparently a direct gap semiconductor with a band gap energy of ~1.95 eV. It was found that the main carrier transportation mechanism for doped, un- doped, and thin films of Zn(_2)SnO(_4) was variable range hopping, with a temperature dependence of the form exp(To/T)'^\ This result was consistent with Hall effect measurements, where high, temperature independent carrier concentrations of about 10(^17) cm(^-3) were obtained, along with low values of carrier mobility ( ~ 1 cm(^2) v(^-1) sec(^-1)) that obeyed the same temperature dependence as the conductivity, [exp(To/T)(^1/4)]

About the new version of maximum principle of Navier-Stokes equations

The below shows the links of the extreme values of the velocity vector, the kinetic energy density and pressure of nonlinear Navier-Stokes equations. The latter shows the validity of the maximum principle for nonlinear Navier-Stokes equations that from a mathematical perspective is fundamentally-ke

Comparative assessment of structural and functional changes in periodontal tissues during prosthetics with metal-ceramic and zirconium dentures

To increase the efficiency of prosthetics, the use of metal, metal-ceramic and zircon dentures was determined. The issues of modern methods of dental prosthetics are highlighted. The analysis of the most common errors and complications in prosthetics with the use of fixed structures has been carried out. The assessment of the physical and technical properties of cermet structures remains poorly studied. To exclude ceramic chips, antagonizing dentures are not brought to contact, which can lead to deformation. Thus, the question of the influence of fixed prostheses on the clinical and morphological state in the absence of periodontal tissues remains unstudied

FREE TOURIST ZONE - A GREAT OPPORTUNITY TO FURNITURE TOURISM IN THE COUNTRY

The following article is about free economic and tourist zone definition and also the work carried out in our country, the role as well as importance of free tourist zones in development of country. Author gave his own suggestions to enhance development of free tourist zones

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В статье показана справедливость простейшего принципа максимума для нелинейных уравнений Навье - Стокса, на основе чего в выбранном пространстве доказаны единственность слабых и существование сильных решений задачи для УНС в целом по времени t ∈ [0 ,Т ] , ∀ Т < ∞

The natural solvability of the Navier-Stokes equations

It is known that the three-dimensional Navier-Stokes equations (ЕNS) the existence theorem of smooth solutions in the presence of smooth data for the whole with respect to time has not proved and the uniqueness theorem is violated in the class of generalized solutions. In a number of works by the author of this article, the results of search studies on the justification of the maximum principle for three-dimensional ЕNS are given. Over time, these studies have improved and later the justice of the simplest principle for maximum was shown for three-dimensional ЕNS. A further continuation of the search led to the determination of the relationship between pressure and the square of the velocity vector modulus from the properties of the ЕNS solutions. On the basis of this the answers to many problematic issues related to the solvability of the ЕNS were found. And in particular, in the selected spaces, the uniqueness of the weak and the existence of strong solutions of the problem for the three-dimensional Navier-Stokes equations for the whole of time are proved

Global solvability of a nonlinear Boltzmann equation

In this paper, based on the splitting method scheme, the existence and uniqueness theorem on the whole time interval t ∈ [0 ,T ) ,T ≤∞ for the full nonlinear Boltzmann equation in the nonequilibrium case is proved where the intermolecular interactions are hard-sphere molecule and central forces. Considering the existence of a bounded solution in the space C, the strict positivity of the solution to the full nonlinear Boltzmann equation is proved when the initial function is positive. On the basis of this some mathematical justification of the H -theorem of Boltzmann is shown

Global solvability of a nonlinear Boltzmann equation

In this paper, based on the splitting method scheme, the existence and uniqueness theorem on the whole time interval t ∈ [0, T), T ≤ ∞ for the full nonlinear Boltzmann equation in the nonequilibrium case is proved where the intermolecular interactions are hard-sphere molecule and central forces. Considering the existence of a bounded solution in the space C, the strict positivity of the solution to the full nonlinear Boltzmann equation is proved when the initial function is positive. On the basis of this some mathematical justification of the H−theorem of Boltzmann is shown

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&nbsp;It was shown that at different stages of drawing training not only the application of knowledge to new conditions, but also the solution of the initial state of the graphic material with a high degree of replacement is an important condition for the development of graphic thinking