Electronic Structure and Piezoelectric Properties of SbSI Crystals

The SbSI crystals are investigated in the paraelectric and ferroelectric phases. The calculations have been performed to find the symmetry and normal coordinates of vibrational modes. We have observed that potential energy with double well create the soft mode of B1u symmetry in the microwave range and semisoft modes in the IR range. The Au and Bg symmetry, top electronic levels of the highest valence band, are degenerate in the paraelectric phase. It is shown that the Jahn-Teller effect is caused by Au symmetry normal mode interacting with the degenerate Au symmetry electronic states in the valence band top. The pseudo-Jahn-Teller effect is induced due to the same mode interacting with Au symmetry electronic states in the valence band and Bg symmetry states in the conduction band bottom. Concerning these two effects, the normal mode force constant K decreases and vibrational constants undergo changes during the phase transition. The theoretical deformation along the crystallographic—x(a), y(b), and z(c)—axes were studied for Sb atoms. The major change of piezoelectric modulus takes place in the ferroelectric phase near the phase transition temperature. At lower temperatures piezoelectric modulus changes become slow. The value as well as anomalous temperature dependence of piezoelectric modulus and Δz(T) is influenced by the change of mean potential energy V¯pz of Sb atoms in soft mode

Puslaidininkinių-feroelektrinių kristalų virpesių spektrų ir elektroninės struktūros tyrimas [rankraštis]

Vytauto Didžiojo universitetasŠvietimo akademij

Puslaidininkinių-feroelektrinių kristalų virpesių spektrų ir elektroninės struktūros tyrimas

Vytauto Didžiojo universitetasŠvietimo akademij

SbO S I kristalų auginimas ir vibracinių spektrų tyrimas fazinių virsmų srityje

Bibliogr. str. galeSbO S I kristalai išauginti iš garų fazės. Šių kristalų atspindžio spektrai ištirti Fourier spektrometru. Optinės konstantos, optinės funkcijos ir vibraciniai dažniai apskaičiuoti Kramers'o ir Kronig'o metoduVytauto Didžiojo universitetasŠvietimo akademij

Origin of ferroelectric phase transition in SbSClxI1−x mixed crystals

art. no. 1450209The measurements of SbSClxI1−x (x = 0.2) temperature dependent capacitance were carried out. The temperature of ferroelectric phase transition TC ≈ 340 K was measured experimentally. TC of SbSClxI1−x was calculated theoretically in anharmonic and harmonic approximations. TC was calculated in anharmonic approximation using temperature dependence of mean potential energy of Sb atoms as a function of the soft B1u symmetry normal coordinate along c(z)-axis. Moreover, TC was calculated in harmonic approximation using temperature dependence of vibrational thermodynamic functions (Helmholc free energy). TC dependence from unit cell parameters a, b and from mixture composition x was carried outVytauto Didžiojo universitetasŠvietimo akademij

Electron charge density investigation in the interatomic bonds of BiSBr and BiSeBr crystals

Vytauto Didžiojo universitetasŠvietimo akademij

Phonon dispersion of SbSBr crystal

Vytauto Didžiojo universitetasŠvietimo akademij

Mechanikos laboratoriniai darbai nespecialistams : mokymo metodinė priemonė

Vytauto Didžiojo universitetasŠvietimo akademij

Investigation of the vibration spectra of a SbSBrxI1-x crystal in harmonic and quasiharmonic approximation

The vibration of spectra SbSBrxI1-x (x = 0 ÷ 0.75) crystal have been determined in quasiharmonic approximation by diagonalization of dynamical matrix. Applying the model atom A with its own parameters (mass and force constants) we were able to get exact normal modes' vibration frequencies. The obtained normal modes' frequencies were superposed with experimental data. It is proved that in Brillouin zone's point k =0 the lower frequency IR (infrared) mode of B1a symmetry and lower frequency R (Raman) mode of B 1g symmetry are soft -alike modes whereas in Brilloun zone's point k = 0.5 an acoustic and Raman mode become active, but lower frequency IR mode becomes inactive. The interaction between phonones creates the anharmonicity of soft-alike IR, R and A vibration modesVytauto Didžiojo universitetasŠvietimo akademij

Origin of ferroelectric phase transition in SbOxS1−xI mixed crystals

art. no. 1550167The dependence of the potential energy V(z) of Sb atoms on B1u symmetry normal coordinates for SbOxS1−xI crystal in ferroelectric phase with a varying mixture x is investigated in the current paper. The potential energy of Sb atoms is characterized by a high anharmonicity within the temperature range 295–377 K. The large anharmonicity of the potential energy V(z) implies that SbOxS1−xI crystals exhibit intermediate behavior between displacement and order–disorder type phase transitions. The phase transition temperature TC depends on the mixture composition xVytauto Didžiojo universitetasŠvietimo akademij