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R. Vlokh

Publications and source records attributed to R. Vlokh.

At least 19 recordsLinked to original sources
arXiv2014

Critical Behavior of Sn2P2S6 and Sn2P2(Se0.28S0.72)6 Crystals under High Hydrostatic Pressures

Basing on the temperature dependences of optical birefringence for Sn2P2S6 and Sn2P2(Se0.28S0.72)6 crystals subjected to hydrostatic pressures, we prove unambiguously that Sn2P2S6 reveals a tricritical point on its (p,T)-phase diagram with the coordinates (p,T) = (4.3 kbar, 259 K), so that the second-order phase transition transforms into the first-order one whenever the pressure increases above 4.3 kbar. We also find that increasing hydrostatic pressure applied to Sn2P2(Se0.28S0.72)6 leads to the change in the phase transition character from tricritical to first-order. Further increase in the pressure up to ~ 2.5 kbar imposes splitting of the first-order paraelectric-to-feroelectric phase transition into two phase transitions, a second-order paraelectric-to-incommensurate one and a first-order incommensurate-to-ferroelectric transition.

cond-mat.mtrl-sci↗
arXiv2007

Phase Coexistence in Cs3Bi2I9 Ferroelastics: Optical, Dilatation and Ultrasonic Velocity Studies

The results for dilatometric, ultrasonic velocity and the domain struct-ure studies of Cs3Bi2I9 crystals in the course of ferroelastic phase trans-ition are presented. It is shown that the phase transition in Cs3Bi2I9 is of the first order. Basing on the thermal expansion results and the data obtained for the elastic stiffness of Cs3Bi2I9 crystals, the latent heat Q=79J/kg at Tc is calculated. The region between 183K and 221K (at cooling) is identified as a heterostructure region, where ferroelastic and paraelastic phases coexist.

cond-mat.mtrl-sci↗
arXiv2007

Piezooptic Properties of beta-BaB2O4 and Li2B4O7 Crystals

Photoelastic coefficients of beta-BaB2O4 and Li2B4O7 crystals are calculated on the basis of piezooptic measurements performed with interferometric technique and the elastic compliance and stiffness data. Using the experimental results, the acoustooptic (AO) figure of merit (FM) has been estimated for the possible geometries of AO interaction. It is shown that the AO FM for the ABO and LTB crystals reach respectively the values M2=243.4*10-15s3/kg and M2=2.57*10-15s3/kg, if the interaction with the slowest ultrasonic waves (v=933.5m/s and v=3173m/s) is concerned. The directions of propagation and polarization of those acoustic waves are obtained on the basis of construction of indicative surfaces of the acoustic wave velocities.

physics.optics↗
arXiv2007

Acoustooptic Interaction in Barium Beta-Borate Crystals

Basing on the measurements of photoelastic coefficients, acoustic waves velocities and the refractive indices, the possible geometries for acoustooptic interaction in b-BaB2O4 crystals have been analysed. It has been shown that the acoustooptic figure of merit achieves its maximum value when the transverse acoustic wave v13 with the velocity 817m/s is propagated in YZ-plane. In this case M2=95.35*10-15s3/kg.

physics.optics↗
arXiv2007

Combined Piezoelectrooptic Effect in Rochelle Salt at the Phase Transition

The results of study of piezoelectrooptic (PEO) effect in the course of ferroelectric-ferroelastic phase transition in Rochelle salt crystals are presented. The coefficient of the combined effect is obtained from measurements of the changes in the electrooptic coefficients under the action of mechanical stress and the changes in the piezooptic coefficients under the action of electric field (or spontaneous polarization). It is shown experimentally that the values of both coefficients are the same, as predicted by the theory. The temperature dependence of the coefficient of combined PEO effect is obtained. Its anomalous behaviour at the phase transition appears due to the dielectric permitivity anomaly. It is also demonstrated that the change in the piezooptic coefficients at the phase transition in Rochelle salt crystals may be satisfactorily explained as a result of linear and quadratic PEO effect induced by spontaneous polarization.

physics.optics↗
arXiv2007

Once More About the "Forbidden" Domain Structure and the Isolated Point in K2Cd2xMn2(1-x)(SO4)3 Langbeinites

The domain structure in K2Cd2xMn2(1-x)(SO4)3 (x=0.5, 0.7 and 0.9) langbeinite crystals is studied with the aid of optical polarization microscopy. It is shown that the domain walls in ferro-elastic langbeinites separate enantiomorphous orientation states. These orientation states appear in the phase with the symmetry 23 in connection with the hypothetic phase transition . In the phase with the symmetry 222, these domain walls are transformed to those separating ferroelastic domains with the opposite signs of enantiomorphism. It is revealed that one enantiomorphous domain can only transform to the other via a thick layer of the parent phase with symmetry. The results for the volume thermal expansion are presented. It is shown that the isolated point at the x,T-phase diagram of K2Cd2xMn2(1-x)(SO4)3 solid solutions corresponds to the concentration x=0.6.

cond-mat.mtrl-sci↗
arXiv2007

Anisotropy of Laser-Induced Bulk Damage of Single Crystals

The regularities of laser-induced damage of anisotropic materials, such as LiNbO3 and KDP dielectric single crystals, are experimentally studied. It is revealed that the shape of laser-induced damage in the dielectric crystals depends on the elastic symmetry of crystal and the propagation direction of the laser beam. When the beam propagates along the optic axis of crystals, the figures of the laser damage are six-path stars for LiNbO3 and four-path ones for KDP crystals. For the direction parallel to X and Y axes in KDP crystal, the damage has initially cross-like configuration, with further splitting of Z-oriented crack into two cracks in the process of damage evolution, leading to transformation of orthogonal-type damage to a hexagonal-type one.

physics.optics↗
arXiv2007

Crystal Optical Properties of Inhomogeneous Plates and the Problems of Polarization Tomography of Photoelastic Materials

Using the Jones matrix formalism, crystal optical properties of inhomogeneous material consisting of a pile of weakly birefringent plates are analysed in relation to the cell model adopted in polarization tomography of 3D dielectric tensor field in photoelastic media. It is shown that the material manifests in general an "apparent" optical gyration caused by different orientations of the plates. Relations between the polarimetric parameters and the dielectric tensor components are ascertained for the case of weak optical anisotropy.

physics.optics↗
arXiv2007

Studies of magnetogyration in cubic Bi12GeO20 crystals using small-angular magnetooptic polarimetry

We present the results of studies for magnetogyration (MG) effect in non-centro-symmetric, non-polar Bi12GeO20 crystals performed with the small-angular polarimetric mapping technique. The magnitude of MG rotation obtained with the small-angular mapping is close to the corresponding values obtained recently on the basis of single-ray polarimetry. Our results demonstrate that multiple reflections of light play a key role in the studies of MG effect in Bi12GeO20 crystals. They lead to the error, which is at least two times as large as the expected value of the MG rotation.

physics.optics↗
arXiv2007

Electrically and magnetically induced optical rotation in Pb5Ge3O11:Cr crystals at the phase transition. 1. Electrogyration effect in Pb5Ge3O11:Cr

We present the results of studies for temperature dependences of electrogyration (EG) effect and natural optical activity in Pb5Ge3O11:Cr crystals. Extremely high magnitude of EG coefficient is found for these crystals. We also demonstrate how the Curie-Weiss constant, the critical exponents of the order parameter and the dielectric permittivity, as well as the coefficients of thermodynamic potential, could be derived from the temperature dependences of optical activity and EG coefficient.

physics.optics↗
arXiv2007

Acoustooptic Diffraction in Borate Crystals

The efficiency of acoustooptic (AO) diffraction in a-BaB2O4 and Li2B4O7 crystals is studied experimentally. The crystals are shown to be quite good AO materials. The efficiency of AO diffraction in a-BaB2O4 reaches h=30% at the electric signal power of P=0.7W for the transverse acoustic wave and 15% at the power of P=0.56W for the longitudinal wave. The same parameter for Li2B4O7 reaches h=21% at P=0,81W for the longitudinal acoustic wave.

physics.gen-ph↗
arXiv2007

Studies of Optical Damage in Photorefractive Single LiNbO3 Crystals using Imaging Polarimetry

The optical damage of photorefractive material, single LiNbO3 crystal, is experimentally studied. The specimen has been illuminated with the radiation of continuous Ar-laser (the wavelength of 488 nm) focused to 35?m spot. The induced birefringence map is obtained by means of imaging polarimeter. Promising resources of the experimental setup for detecting laser-induced damage in photorefractive materials is demonstrated.

physics.gen-ph↗
arXiv2007

Optical Birefringence and Domain Structure of the as-grown Rb2xTl2(1-x)Cd2(SO4)3 Solid Solutions at Phase Transitions

It is shown that the as-grown solid solutions Tl2xRb2(1-x)Cd2(SO4)3 possess a residual optical birefringence in the cubic phase at room temperature. The existence of both the residual birefringence and the residual domain structure in the compound with x=0.8 at the room temperature, along with the domain walls orientation and the orientation of extinction positions of the neighbouring domains, indicate that the above domain structure corresponds to "forbidden" ferroelastic domains of the phase P212121. On the basis of measurements for the temperature variation of the birefringence and observations of the domain structure transformations, one can conclude that the phases with the symmetries P213 and P21 coexist above Tc1 in the compounds with x = 0.7 - 1.0. The phase transition temperatures Tc1, Tc2, and Tc3 obtained from the temperature birefringence variations agree well with those obtained previously, using the studies of thermal expansion and ultrasonic wave velocities.

cond-mat.other↗
arXiv2007

Indicative Surfaces for Crystal Optical Effects

This paper has mainly a pedagogical meaning. Our aim is to demonstrate a correct general approach for constructing indicative surfaces of higher-rank tensors. We reconstruct the surfaces of piezo-optic tensor for beta-BaB2O4 and LiNbO3 crystals, which have been incorrectly presented in our recent papers.

physics.optics↗