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First principles investigations of HgX (X=S, Se and Te)

Düz I., Erdem I., Ozdemir Kart S., Kuzucu V.

Archives of Materials Science and Engineering

2016

Vol. 79, nr 1

5--11

Purpose: The aim of this study is to determine the structural, and mechanical properties of Hg chalcogenide materials (HgX; X=S, Se, Te) in the zinc-blende structure which are presented as promising candidates for modern optoelectronic and spintronic applications. The dependence of elastic constants of pressure for three materials are evaluated. Moreover, isotropic mechanical properties such as bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio are obtained. Design/methodology/approach: First principles calculations based on Density Functional Theory are performed by employing Projector Augmented Waves potentials. The electronic exchange and correlation function is treated by using Generalized Gradient Approximation parametrized by Perdew, Burke and Ernzerhof (PBE96). Findings: Calculated results of structural and mechanical properties are in good agreement with those of experimental and other theoretical studies. This three materials in zinc-blende structure are mechanically stable. İsotropic mechanical properties are also obtained. Resistance against both linear strain and shear strain and ductility decrease as we go into the sequence of HgS−>HgSe−>HgTe. The wave velocities and Debye temperatures calculated for this materials. Debye temperatures are founded for HgS, HgSe and HgTe as 306.21 K, 264.30 K and 240.19 K, respectively Research limitations/implications: Calculation speeds of the computers and data storage are some limitations. Also, the lack of experimental data hinder for the comparison of our results. Practical implications: Obtaining high pressure elastic constants by calculations is preferable since it is very difficult or even impossible to measure them by experimentally. Originality/value: There are only restricted number of investigation of elastic constants of mercury chalcogenides both theoretically and experimentally.

A method for correction of elastic and piezoelectric constants of crystals using measured surface acoustic wave parameters

Brzozowski E.

Materiały Elektroniczne

2011

T. 39, nr 2

8-13

Surface acoustic wave (SAW) properties of a crystal depend on the density, elastic, piezoelectric and dielectric constants.On the basis of literature data, calculations of SAW parameters in a neodymium calcium oxoborate [NdCa4O(BO3)3] crystal were carried out to evaluate orientations optimal for the correction of elastic and piezoelectric constants. SAW velocities and electromechanical coupling coefficients were measured using SAW delay lines deposited on differently oriented crystal substrates. Dielectric constants were determined from measured effective permittivities. Both a nonlinear least squares algorithm and a computer program for the correction of elastic and piezoelectric constants from measured SAW velocities and electromechanical coupling coefficients were developed. The correction of NdCa4O(BO3)3 elastic and piezoelectric constants was carried out. It was shown that for the corrected constants the differences between the measured and calculated SAW parameters are marginal.

Własności akustycznych fal powierzchniowych (AFP) w rysztale zależą od gęstości stałych elastycznych, piezoelektrycznych i dielektrycznych. Na podstawie danych z literatury obliczono parametry AFP w krysztale tlenoboranu neodymowo wapniowego [NdCa4O(BO3)3] w celu wyznaczenia orientacji optymalnych do korekcji stałych. Zmierzono prędkości i współczynniki sprzężenia elektromechanicznego AFP z wykorzystaniem linii opóźniających osadzonych na podłożach NdCa4O(BO3)3 o różnych orientacjach. Wyznaczono stałe dielektryczne z pomiaru przenikalności elektrycznych. Opracowano metodę korekcji stałych elastycznych i piezoelektrycznych wykorzystującą nieliniowy algorytm najmniejszych kwadratów i zmierzone parametry AFP. Przeprowadzono korekcję stałych elastycznych i piezoelektrycznych kryształu NdCa4O(BO3)3. Wykazano, że dla stałych skorygowanych różnice między zmierzonymi, a obliczonymi parametrami AFP są bardzo małe.