On the Determination of Birefringence of Liquid Crystals by the Interference Method

A new method of processing the experimental data in the interference method for the determination of birefringence of liquid crystals which allows obtaining results in good agreement with those from prism or wedge methods, is presented.     

The Discovery of the Diffraction of X-rays in Crystals — A Historical Review

The history of the discovery of X-ray diffraction in crystals and its first sequels are reported; the life of M. v. Laue, the discoverer and founder of a first basic theory, and of P. P. Ewald, who contributed to the discovery and to later developments of the theory, are shortly described.     

Study on the Phase equilibrium in the Systems Sodium Selenate — Cadmium Selenate — Water and Sodium Selenate — Manganese Selenate — Water at 25 °C

The phase equilibrium in the systems Na₂SeO₄ CdSeO₄ H₂O and Na₂SeO₄ MnSeO₄ H₂O were studied and it was established that new phases were obtained — double salts with a composition: Na₂Cd(SeO₄)₂ · 2 H₂O and Na₂Mn(SeO₄)₂ · 2 H₂O. The fields of phase equilibrium of the double salts in the triple systems were determined. The composition of the new phases and the number of the water molecules of crystallization were investigated, respectively by the Schreinemackers' method of physico-chemical analysis and thermogravimetrical analysis. An X-ray diffraction analysis of the new phases obtained was done.     

Bridgman Growth and Characterization of LuAlO3—Ce3+ Scintillator Crystals

Chemical and structural effects in LuAlO₃-Ce³⁺ single crystals grown by the Bridgman method were studied using spectral emission, x-ray, etching and optical techniques. The Ce concentration distribution was found to exhibit the normal freeze behavior with partition coefficient of 0,17. The expansion of the unit cell volume due to incorporation of Ce was measured. Dislocation etch pits were revealed on (010), (100) and (001) crystal faces. Thermal expansion behavior of LuAlO₃ was studied along the major crystallographic axes in between the room temperature and 1000 °C. The scintillation performance of 5 × 5 × 10 mm³ samples was measured using a 662 keV gamma source with a shaping time of 1.2 μs. The light yield was increasing from 40% BGO to 70% BGO with increasing of the Ce³⁺ content from 0.13 at.% to 0.9 at.%.     

Atomic Force Microscopy Determination of the Direction of Dislocation Lines in Single Crystals of Bismuth and Its Alloys

Crystallography Reports - A technique for determining the directions of dislocation lines using an atomic force microscope after selective etching of a single crystal is discussed. The technique...     

The Microhardness and the Toughness Anisotropy of Paratellurite Single Crystals in the Tr — 650 °C Temperature Range

The temperature hardness (H_v) and toughness (K_1C) dependence of paratellurite (100), (010), (001) planes is investigated in the T_r −650 °C range. The correlation between the anisotropy degree of Young modulus and H_v is not found. The presence of 11 kind H_v and K_1C anisotropy is shown.     

Lattice constants and site preference in the system Ni2SiO4—Co2SiO4

Most important supposition for a possible site preference in a olivine solid-solutions are besides the different crystal chemical properties of M cations (size, electronegativity, crystal field stabilization energy) the differences between the both octahedral coordinated sites M1 and M2 of the olivine structure. Using this regularities the site preference in the system Ni Co olivines is predicted. If site preferences are existing, it is possible to deduce deviations of the Vegard's rule in the system Ni₂SiO₄—Co₂SiO₄ using geometrically-structurally considerations. The plot of experimentally determined lattice parameters in this solid solutions system shows the existing of the proposed deviations of the Vegard's rule and evidences the site preferences of Ni²⁺ in the M1- and Co²⁺ in the M2 octahedra only by determination of lattice parameters.     

Growth of Ge1—xSix (x= 0 to 0.5) Single Crystals by a Zone Melting Method

Ge_1—xSi_x graded crystals with 0 < x < 0.66 were grown by a zone melting method in a double ellipsoid mirror furnace. They have a diameter of 9 mm and grown lengths between 27 and 80 mm. Single crystalline regions reached a maximum Si concentration of 50 at%, determined by EDX and ECP measurements. Starting with a Ge seed, a defined concentration profile was obtained by a wedge-shaped arrangement of the feed material. The concentration profiles could be predicted by a simulation program.     

Neutronographical investigations of the age hardening behaviour on Iron — Manganese — Nickel alloys

Age hardenable martensitic Iron—Manganese—Nickel alloys were neutronographically investigated in order to explain the age hardening effect occurring during the heat treatment. The formation of coherent precipitations of an ordering phase within the matrix proved to be the reason for the occurring hardness increase.     

Surface morphology of iron specimens boronized with BCl3—H—mixtures (I) influence of process parameters

Specimens made of armco iron were boronized with 1.1 Vol.% BCl₃ in H₂ at 1023 K, 1123 K, and 1223 K during different periods. Afterwards, their surfaces were examined by scanning electron microscopy. As a result of variation of the process parameters the surface morphology of the boride layers formed was changed. The etch attack of the boronizing gas mixture on the substrate may be reduced by appropriate parameters.     

X-ray determination of solid solution composition in the melilite system åkermanite (Ak) — gehlenite (Ge) — soda melilite (Sm)

Expressions are given and discussed which allow a determination of the composition of solid solutions in the ternary system Ak Ge Sm. Resulting from X-ray measurements of the tetragonal melilite constants a₀ and c₀, the composition can be calculated within the limits of ±3% if the lattice constants are determined with an accuracy of ±0.001 Å.     

The Characteristics of the Mixed Crystals of the KNO3‐NH4NO3‐H2O System at 298 K

The equilibrium studies of the KNO₃‐NH₄NO₃‐H₂O system at 298 K have been conducted. The isotherm of solubility and the curve of distribution have been mathematically described. The parameters of the crystal lattice and the enthalpy of crystallization of the [K_x(NH₄)_1‐x]NO₃ solid solutions as a function of their composition have been presented. The structure of salts KNO₃�xNH₄NO₃ with different x values have been solved and refined.     

Synthesis and Characterisation of Bulk Textured Phases in the Bi(Pb)—Sr—Ca—Cu—O System

Growth of lead-doped textured Bi-cuprate, using an immersed heater floating zone (TSFZ) apparatus, from a narrow supercooled melt created an essentially dense structure consisting of locally aligned long platelet crystal grains. The extended grains have their long axes parallel to the growth axis with a low angle misorientation. The effect of gas bubbles and the pulling rates on the microstructure and superconducting transition temperature of the textured boules have been studied. The decomposing nature of the 2223 phase on melting leads to form the energetically favourable low T_c 2212 phase.     

In Situ Reflection Electron Microscopy for the Analysis of Silicon Surface Processes: Sublimation,Electromigration, and Adsorption of Impurity Atoms

Crystallography Reports - The results of recent studies of the structural morphological transformations of Si(111) and Si(100) surfaces using in situ ultrahigh-vacuum reflection electron microscopy...     

Mechanical Behaviour of LiF Single Crystals in Compression and Tension at Temperatures from −196°C to 800°C

The work hardening characteristics of LiF single crystals in compression and tension has been investigated as a function of temperature. It was shown that in temperature range from 200 °C to 600 °C four stages of hardening were observed and the main part of plastic flow proceeds in stage IV. The parabolic hardening was not observed. The flow stresses and hardening rates in all stages in compression are higher than those in tension. As a temperature increase this difference decreases. The hardening rates, stresses which correspond to the beginning of the linear hardening stages and the duration of those stages decrease as a temperature increase. At temperatures above 600 °C the yield drop occured. Taking into account a good agreement between the temperature dependences of the critical resolved shear stress and τIII the assumption was made that τIII corresponds to resolved shear stress in a secondary glide system.     

LGAS晶体的微结构及声表面波特性研究

本文采用第一性原理计算了La3Ga5-xSiAlxO14 (LGAS)压电晶体几何结构、能带和态密度.并研究了其在X、Y和Z切型的声表面波速度、机电耦合系数及能流角.当x=0.5时,构建了La3Ga4.5SiAl0.5O14晶体的1×1×2超晶胞结构,发现A1原子替代2d四面体位置的Ga原子时体系总能量最低,体积最小,因此是最稳定的状态.与石英相比,LGAS具有声表面波速度较低、机电耦合系数较大且存在能流角为零的切型等优点.掺Al元素降低了成本但对结构和声表面波特性影响不大.Y切0是较好的切型,可用于制备声表面波器件.     

On the Density of Synthetic Glasses in the System Soda Melilite – Gehlenite/Ákermanite

The solid density has been determined at 25°C by hydrostatic weighing along the binary systems Sm–Ge₅₀Åk₅₀ and Sm–Ge₇₀Åk₃₀. The molar volume V decreases linearly with increasing mole fraction of Ge_mÅk_n, x_B, according to δV/δx_B = −5.08 cm³ mol⁻¹ and −4.40 cm³ mol⁻¹ for Ge₅₀Åk₅₀ and Ge₇₀Åk₃₀, respectively. The results enable the molar fraction x_B to be determined from density measurements with an absolute error of ±5 mol%.     

Experimental Study of Interface Inversion of Tb3ScxAl5‐xO12 Single Crystals Grown by the Czochralski Method

Thermal conditions and rotation rate were examined experimentally for obtaining a flat interface growth of high melting‐point oxide (Tb₃Sc_xAl_5‐xO₁₂ ‐ TSAG) by the Czochralski method. The critical crystal rotation rate can be significantly reduced, of about twice at low and very low temperature gradients comparing to medium temperature gradients in the melt and surroundings of the crystal. The interface shape of TSAG crystals is not very sensitive on crystal rotation rate at small rotations and becomes very sensitive at higher rotations, when the interface transition takes place. The range of crystal rotation rates during the interface transition from convex to concave decreases with a decrease of temperature gradients. At low temperature gradients interface inversion crystals takes place in very narrow range of rotation rates, which does not allow one to growth such crystals with the flat interface. Even changing crystal rotation rate during the growth process in a suitable manner did not prevent the interface inversion from convex to concave and thus did not allow to obtain and maintain the flat interface.