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Thermal conductivity of silicon doped by phosphorus: ab initio study

100%

Andriyevsky B. , Janke W. , Stadnyk V. Y. , Romanyuk M. O.

Materials Science Poland

2017

tom Vol. 35, No. 4

717--724

An original approach to the theoretical calculations of the heat conductivity of crystals based on the first principles molecular dynamics has been proposed. The proposed approach exploits the kinetic theory of phonon heat conductivity and permits calculating several material properties at certain temperature: specific heat, elastic constant, acoustic velocity, mean phonon scattering time and coefficient of thermal conductivity. The method has been applied to silicon and phosphorus doped silicon crystals and the obtained results have been found to be in satisfactory agreement with corresponding experimental data. The proposed computation technique may be applied to the calculations of heat conductivity of pure and doped semiconductors and isolators.

Optical properties of D-serine doped TGS crystals for pyroelectric sensors

75%

Kurlyak V. Y. , Stadnyk V. Y. , Andriyevsky B. V. , Romanyuk M. O. , Kohut Z. O. , Gaba V. M.

Materials Science Poland

2015

tom Vol. 33, No. 4

692--698

Refractive and birefringence indices in the range of transparency of 300 to 700 nm for triglycine sulphate crystals doped with D-serine molecules have been measured in the temperature range of 290 K to 340 K. The obtained optical properties are discussed together with characteristic electrical features of these materials used as pyroelectric sensors for measurement of temperature. The experimental results obtained in this study will be necessary as the reference data for comparison with the calculated refractive indices of TGS + D-serine on the basis of density functional theory. Determination of the proper position of D-serine, will reveal the features of TGS + D-serine crystal structure necessary to achieve stable unipolarity.

Influence of uniaxial stresses on electronic and opticalproperties of β-K2SO4 crystal

75%

Andriyevsky B. , Jaskólski M. , Stadnyk V. Y. , Romanyuk M. O. , Kashuba Z. O. , Romanyuk M. M.

Materials Science Poland

2015

tom Vol. 33, No. 1

11--17

In view of possible practical applications of transparent crystals for mechanical stress sensors, theoretical investigation of piezo(elasto)optic effect in crystals might be useful for searching for proper materials, possessing large coefficients of elasto-optic effect, and for determination of uniaxial stress directions of maximum piezo-optical sensitivity. The influence of the uniaxial stresses on the electronic band structure, density of states, and optical properties of potassium sulphate crystal β-K2SO4 have been studied in the framework of the density functional theory using the ab initio CASTEP code. Increase in the band gap, Eg of the crystal takes place for three crystallographic directions and for moderate uniaxial stresses, σ< 1.5 GPa. Dependencies of principal refractive indices and polarizabilities upon principal uniaxial stresses are discussed together with other features of electronic structure of the crystal.