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Ovsiannikova L.,Frantsevich Institute for Problems of Materials Science
Acta Physica Polonica A | Year: 2012

The electronic structure of the ground state of fullerene-like and wurtzite-like ZnnOn and Znn-xCd xOn clusters has been investigated by computer physics methods. A relative evaluation of the stability and band gap width of clusters depending on the number of atoms in the cluster and its geometry has been performed. The model of a fullerene-like (ZnO)60 particle with a mixed sp3/sp2 type of bonds has been constructed. A (ZnO)12 cluster of Th symmetry was taken as a base of the model. Within the framework of the B3LYP electron density hybrid functional method with a set of 3-21G(d) split valence basis functions, a numerical investigation of the influence of the incorporation of cadmium (33%) into the ZnO matrix on the electronic structure and the band gap width has been performed.

Shtepliuk I.I.,Frantsevich Institute for Problems of Materials Science
Superlattices and Microstructures | Year: 2014

Numerical simulations of Zn1-xCdxO/ZnO- based resonant tunneling diode structures are presented, employing the transfer matrix formalism and the Tsu-Esaki model. The factors influencing on the effective electron mass of the two-dimensional electron gas in the Zn 1-xCdxO/ZnO heterointerface - a conduction band nonparabolicity, a quantum confinement and a polaron effect - were analyzed and evaluated. The simulated current-voltage characteristics show a strong dependence on a well width, a barrier thickness and an internal electric field induced by a spontaneous and a piezoelectric polarization. © 2014 Elsevier Ltd. All rights reserved.

Ovsiannikova L.,Frantsevich Institute for Problems of Materials Science
Acta Physica Polonica A | Year: 2013

The structural, cohesive, and electronic properties of a fullerene-like (ZnO)60 cluster with a shell of diamond- -like structure with sp 2=sp3 bonds have been investigated in comparison with those of clusters differing in geometry and composed of the equal number of ZnO structural units (clusters of fullerene, onion, and coordination tetrahedron) within the framework of the electron density hybride functional method (B3LYP) with a set of 6-31G(d) split valence basis functions. The fullerene-like (ZnO)60 cluster is used as a model in an investigation of the change in the band-gap width (the decrease in the band-gap width is ~ 0.2 eV) in the case of the substitution of Zn atoms by Cd atoms (20% of substitution) in the ZnO matrix in ZnCdO ternary structures.

Kovalchenko M.S.,Frantsevich Institute for Problems of Materials Science
International Journal of Refractory Metals and Hard Materials | Year: 2013

The rheological model of deformable, irreversibly compressible, porous body based on mechanics of continua, and creep theory of crystalline materials, is used to describe quantitatively the compaction of the tungsten and titanium carbides powders under pressure sintering in isothermal conditions. Densification of the porous body occurs under action of Laplace's pressure, generated by surface tension, and applied pressure. The estimated mean value of Laplace's pressure was determined to be 5.8 MPa for tungsten carbide and 7.2 MPa for titanium carbide. The densification kinetics of tungsten carbide in the sintering range of 2100-2500 C and titanium carbides in the sintering range of 2100-2700 C are controlled by the mechanism of nonlinear steady-state creep, which occurs at a rate proportional to the fourth power of stress in carbide matrix forming porous material. The estimated values of activation energy for the powder particle power-law creep rate are 591 kJ/mol for tungsten carbide and 573 kJ/mol for titanium carbide during the pressure sintering in initial and intermediate stages. These values indicate that a climb dislocation mechanism controlled the creep, and the values are consistent with the activation energies of bulk diffusion in metal sublattice of carbides. A diffusional creep controls the pressure sintering kinetics in a later stage. © 2013 Elsevier Ltd. All rights reserved.

Brus V.V.,Frantsevich Institute for Problems of Materials Science
Solar Energy | Year: 2012

A simple approach for the calculation of the width of the space charge region (and consequently the concentration of uncompensated acceptors), which takes into account the effect of the series resistance on the quantum efficiency of anisotype asymmetrical thin film heterojunction solar cells (on the example of CdS/CdTe solar cells), was proposed. The effect of the light dependent series resistance and current transport mechanism was also taken into consideration. © 2011 Elsevier Ltd.

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