Structural and magnetic phase transitions in KMnF<Subscript>3</Subscript>

The dielectric and magnetic measurements of the KMnF₃ crystals obtained by the Czochralski and Bridgman methods have been performed. Three structural transitions have been observed in the crystals. The mutual arrangement of the temperature of magnetic ordering and the temperature of the lower structural transition determines the number and type of magnetic transitions in these crystals.     

Raman,Infrared and Calorimetric Investigations of Solid Phases Formed by 4-Nitrophenyl 4-n-Octyloxy-benzoate

Among more than several thousand papers dealing with the nesophase, surprisingly low - only 10-15 is the number of the publications dedicated to the solid state of liquid crystals and especially to the various metastable and glassy modifications formed by fast cooling of the mesophase. The glassy state of a liquid crystal was first established for cholesteryl hydrogen phthalate^/1/. Later, the formation of metastable state by supercooling of the mesophase has been reported by a number of research workers using X-ray diffraction, optical microscopy, molecular spectrosco-     

Optical phonons in Rb<Subscript>2</Subscript>TeBr<Subscript>6</Subscript> and Cs<Subscript>2</Subscript>TeBr<Subscript>6</Subscript> crystals

Raman scattering in Rb₂TeBr₆ and Cs₂TeBr₆ crystals is studied. The phonon spectra of the crystals are calculated using the factor group method. The number of Raman-active modes, their symmetries, and selection rules are found. Observed Raman spectrum lines are identified with atomic vibration modes of the crystal.     

Acoustogyration diffraction of optical waves: case of SiO<Subscript>2</Subscript> and TeO<Subscript>2</Subscript> crystals

Interaction of acoustic and light waves with accounting for elastooptic and elastogyration effects is theoretically described. Collinear acoustogyration diffraction in quartz and paratellurite crystals is experimentally investigated and thoroughly analyzed. Piezogyration effect is experimentally studied for TeO₂ crystals. The acoustogyration efficiency and the acoustogyration figure of merit calculated for a number of crystals (GaAs, TeO₂ and SiO₂) are shown to be too small for experimental detection. On the other hand, we demonstrate that the light diffraction at periodical distribution of the imaginary part of dielectric permittivity related to the piezogyration effect should, in principle, be observed for the case of interaction of optical waves with enantiomorphous ferroelastic domain structure and in cholesteric liquid crystals.     

A collection of 505 papers on false or unconfirmed ferroelectric properties in single crystals,ceramics and polymers

This collection presents 505 papers on ferroelectricity in single crystals, ceramics and polymers in which pointed or elliptical hysteresis loops would testify to their ferroelectric properties. In some papers, the authors ensure that ferroelectricity can occur even in materials that do not have a polar axis of symmetry.     

Calculation of the growth kinetics and dispersity of K<Subscript>2</Subscript>SO<Subscript>4</Subscript> crystals in drops of an evaporating solution

Experimental data on the evaporation kinetics of saturated K₂SO₄ solution drops and the nucleation kinetics of the first crystals are used to develop a simple procedure for the calculation of the solution concentration and the number, size, and dispersity of growing crystals. The calculation results agree well with the experimental data on the growth kinetics of K₂SO₄ crystals and their dispersity after complete evaporation of water. The dispersity of crystals is shown to linearly depend on the reciprocal time of evaporation of drops having different initial heights.     

Nonlinear-laser effects in χ(<Superscript>3</Superscript>)-and χ(<Superscript>2</Superscript>)-active organic single crystals

The process of stimulated Raman scattering (SRS) allows one to convert laser emission wavelength of crystals, providing suitable molecular or lattice modes which contribute to third-order nonlinear optical susceptibility. Renewed interest in this field emerged because of the discovery of SRS in crystals that contain molecular units exhibiting Raman active modes. Particularly, organic nonlinear optical crystals used so far for frequency doubling and third harmonic generation seem to have a great potential for SRS application. This review paper reported same results on efficient SRS lasing effects that were discovered recently in organic crystals.     

One-Particle Distribution Functions and Thermodynamics of Crystals with Many-Body Forces. III. Perturbation Theory

The theory of crystalline state described in preceding papers is considered as a zeroth-order approximation. Statistical perturbation theory is used for the purpose of improving this approximation. The second-order corrections to the Helmholtz free energy and thermodynamic properties of strongly anharmonic crystals are derived. The properties of solid Ar, Kr, and Xe are calculated using various pair-potential functions in conjunction with the AXILROD -TELLER -MUTO three-body potential. The first quantum corrections are taken into account in the quasi-classical approximation. The result of computations are compared with the experimental data.     

Anomalies in the pyroelectric properties of LiNbO<Subscript>3</Subscript> crystals of the congruent composition

A number of anomalies are revealed in the temperature dependence of the primary pyroelectric coefficient for single-domain crystals of lithium niobate LiNbO₃ in the temperature range 310–330 K. It is shown that these anomalies are associated with the transformation of the domain structure of the lithium niobate crystals. The problem regarding the correct performance of the pyroelectric measurements and the possible influence of the observed effects on the optical properties of lithium niobate crystals and on the recording of optical phase holograms are discussed.     

Calculation of nonlinear optical polarization and phase matching in biaxial crystals

We present a general, analytical formula for the calculation of the unit vectors of the direction of vibration of the electric field strength in biaxial crystals. By means of this formula it is possible to calculate the effective nonlinearity for second-order nonlinear optical frequency conversion processes in biaxial crystals. For two highly efficient nonlinear optical crystals we have calculated the effective nonlinear susceptibility and walk-off angles. The results have been compared with numerical as well as experimental data of previous papers.     

The nature of magnetoelastic anomalies in Nd<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>MnO<Subscript>3</Subscript> upon suppression of charge ordering by a magnetic field

This paper reports on the results of investigations into the magnetic and magnetoelastic properties of Nd_0.5Sr_0.5MnO₃ single crystals in pulsed magnetic fields up to 250 kOe, the magnetic and kinetic properties of these crystals in weak static magnetic fields, and their thermal expansion. It is demonstrated that the studied properties exhibit a number of anomalies due to a transition from the antiferromagnetic semiconducting state to the ferromagnetic metallic state upon suppression of charge ordering.     

NaBi(WO<Subscript>4</Subscript>)<Subscript>2</Subscript>: In Cherenkov crystals for electromagnetic calorimetry

NaBi(WO₄)₂:In (called NBW) colorless Cherenkov crystals were synthesized and studied. A decrease in the concentration of color centers provides a 50-nm blueshift of the optical transmission spectrum of NBW crystals. Upon exposing these crystals to gamma rays at a dose of 3 · 10⁷ rad, the optical transmission spectra in these crystals remain almost the same. The energy resolution (calculated by the Monte Carlo method) of calorimeters based on NBW crystals of different compositions is discussed.     

Broadening of IR Absorption Bands of p-Methoxybenzylidene p,n-Butylaniline (MBBA) Under the Influence of an A.C. Electric Field

Abstract

Infrared and Raman spectroscopy has been widely used at last decade to elucidate the properties of liquid crystals, the structure of the liquid crystal molecules and the molecular motion in various types of mesophase¹. Among more than 50 papers dealing with liquid crystals only a few consider the influence of electric field on mesophase vibrational spectrum. First Nelf² has used the electric field to orient nematic sam ples of p-methoxybenzylidene p′-cyanoaniline for the investigations of IR dichroism. Assuming that a large liquid crystal line domain acts like a rigid dipole and taking into account the effects of the walls an expression for the dichroism ratio was derived to evaluate the degree of orientational order. Later, Ohnishi³ has applied a d.c. electric field to a cell filled with MBBA and studied the changes in the relative transmittance of some bands in the region 4000–1000 cm^?1 of the dynamic scattering mode. Pan and Wang⁴ found that in the presence of turbulence due to the application of electric field, the intensity of all Raman bands decreases drastically but without any shift in the peak positions.     

X-ray scattering factors for ionic crystals with complete electron shells

Scattering factors for ionic crystals with complete electron shells were considered by employing radially deformed atomic wave functions for “crystal ions”. The deformation was taken into account by the scaling method introduced by Mansikka in his earlier work. The correction due to the overlap between the deformed ions in crystals were evaluated by means of the formulae presented in our previous papers. Scattering factors for LiF and NaF crystals were computed and compared with experimental data. The effect of deformation is comparable in magnitude with the overlap ones.     

Luminescence and thermally stimulated recombination processes in Li<Subscript>6</Subscript>Gd(BO<Subscript>3</Subscript>)<Subscript>3</Subscript>:Ce<Superscript>3+</Superscript> crystals

The luminescence and thermally stimulated recombination processes in lithium borate crystals Li₆Gd(BO₃)₃ and Li₆Gd(BO₃)₃:Ce have been studied. The steady-state luminescence spectra under X-ray excitation (X-ray luminescence), temperature dependences of the intensity of steady-state X-ray luminescence (XL), and thermally stimulated luminescence (TSL) spectra of these compounds have been investigated in the temperature range of 90–500 K. The intrinsic-luminescence 312-nm band, which is due to the ⁶ P _J → ⁸ S _7/2 transitions in Gd³⁺ matrix ions, dominates in the X-ray luminescence spectra of these crystals; in addition, there is a wide complex band at 400–420 nm, which is due to the d → f transitions in Ce³⁺ impurity ions. It is found that the steady-state XL intensity in these bands increases several times upon heating from 100 to 400 K. The possible mechanisms of the observed temperature dependence of the steady-state XL intensity and their correlation with the features of electronic-excitation energy transfer in these crystals are discussed. The main complex TSL peak at 110–160 K and a number of minor peaks, whose composition and structure depend on the crystal type, have been found in all crystals studied. The nature of the shallow traps that are responsible for TSL at temperatures below room temperature and their relation with defects in the lithium cation sublattice are discussed.     

Coherent X‐ray diffractive imaging of protein crystals

The technique of coherent X‐ray diffraction imaging (CXDI) has recently shown great promise for the study of inorganic nanocrystals. In this work the CXDI method has been applied to the study of micrometer‐size protein crystals. Finely sampled diffraction patterns of single crystals were measured and iterative phase‐retrieval algorithms were used to reconstruct the two‐dimensional shape of the crystal. The density maps have limited reproducibility because of radiation damage, but show clear evidence for crystal facets. Qualitative analysis of a number of single‐crystal diffraction peaks indicates the presence of inward surface contraction on 2 µm size crystals. A survey of several hundred diffraction patterns yielded a number of examples with dramatic single‐sided streaks, for which a plausible model is constructed.     

气相外延ZnSe单晶薄膜的蓝色电致发光

本文在300℃—700℃温度范围内,在GaAs衬底上气相外延生长了ZnSe单晶薄膜。讨论了衬底温度对外延层电学性质及光学特性的影响。ZnSe外延层经Zn气氛热处理后,发光特性大为改善。用处理后的ZnSe外延膜做成MIS发光二极管,首次得到了室温下气相外延ZnSe单晶薄膜的蓝色电致发光。     

Optical and Scintillation Properties of NaI(Tl) Crystals

Using absorption spectroscopy and luminescent methods, we have investigated qualitatively dissimilar NaI and NaI(Tl) crystals. It is established that in NaI(Tl) crystals grown under conditions of melt hydrolysis and interaction with the air components, centers of additional luminescence of nonactivation nature are formed that decrease the transparency in the activator-radiation region. Data on the hole nature of these centers are obtained. It is shown that high-temperature annealing can alter the number of centers responsible for the decrease in the transparency of the NaI(Tl) crystals.     

Republication of: Einsteinian <Emphasis Type="Italic">ds</Emphasis><Superscript>2</Superscript> in Newtonian fields. IX: The analog of the logarithmic potential

This is an English translation of the second of two papers by Tullio Levi-Civita, first published in 1917 and 1919. The papers are remarkable as being among the earliest in which exact solutions of Einstein’s equations were derived. Of the two solutions presented, the first (republished as an accompanying Golden Oldie) is better known today as the Bertotti-Robinson solution, and the second one (republished as this Golden Oldie) is the gravitational field of an infinite cylinder. The papers have been selected by the Editors of General Relativity and Gravitation for republication in the Golden Oldies series of the journal. This republication is accompanied by an editorial note written by Malcolm MacCallum, and by a brief biography of the author, compiled from internet sources by Andrzej Krasiński.     

The effect of total internal reflection of wave beams in nonlinear media

The recent papers that consider new effects attributed to the total refection of a weak beam at a more powerful beam with another frequency in nonlinear media are reviewed. As an example, the dynamics of the beam reflection in media with thermal nonlinearity and photorefractive crystals are analyzed.