Hydrothermal crystal synthesis in the Ho2O3(Yb2O3)GeO2KFH2O systems

Crystallization in the Ho₂O₃(Yb₂O₃)GeO₂KFH₂O systems has been investigated under hydrothermal conditions. Crystallization fields of the crystalline phases have been determined. Single crystals of Ho₂Ge₂O₇, Yb₂Ge₂O₇ (two types), K₂HoF₅, K₂YbF₅, K_xYb_yGe_pO_q (P-type), Ho(OH)₃, Yb(OH)₃, and K₂Ge₄O₉ have been obtained. The germanates synthesized have been studied by X-ray analysis and infrared-spectroscopy. Diorthogermanate Yb₂Ge₂O₇ has been found to crystallize in two structural types; the first is characterized by the usual structure that is typical for rare-earth germanates, the second is new for germanates of rare-earth elements. High chemical resistance is typical of these crystals. The P-type germanate also has a new type of structure among rare earth germanates. Some suggestions are made as to the structure of these new germanates on the basis of X-ray and ir-spectroscopic data.     

Temperature dependence of the lasing efficiency of the three-micrometer YAG:Er laser

Experimental results and calculated data on the study of the temperature dependence of the lasing efficiency of the pulsed three-micrometer YAG:Er³⁺ laser in the range T = ?80 ? +80°C are presented. It was shown that a decrease in the laser crystal temperature from room temperature to T = ?80°C leads to an increase in the laser output energy by a factor of 3?4 at the same energy of lamp pumping. Accordingly, the differential lasing efficiency increases (about three times).     

On the growth mechanism of sodalite single crystals grown by the hydrothermal method on single crystal seeds coated with informative informative interfacial layers

The growth mechanism of the early formation stages of sodalite single crystals grown by the method of hydrothermal synthesis on single crystal seeds coated with interfacial layers of polycrystalline silver has been studied at an electronmicroscopic scale. Coating with interfacial layers leads to a very weak adhesion between the overgrown single crystal and the surface of the interfacial layer on top of the seed, thus providing a unique possibility of detaching the overgrown single crystals from seeds and investigating the very early crystallization stages by the morphology of the growth surface. In local microregions of seed surfaces coated with interfacial layers discrete particles arise differing from one another in morphology, this being primarily associated with the electrical heterogeneity of seed surfaces. During crystallization, the space between the discrete particles was filled with the hydrothermal solution which represented a liquid interfacial layer exhibiting informative properties occurred under the influence of electrically active elements of the seed surface. At the boundary separating the liquid interfacial layers with particular informative properties from the rest of the solution volume, at early crystallization stages, together with the formation of discrete particles directly on the coated seed surface, growth of a continuous sodalite single crystal took place. The informative properties of seed surfaces, which are regularly modified due to coating with interfacial silver layers, determine the occurrence on local regions of seed surfaces (under appropriate crystallization conditions) of one or the other polymorphous modification: either hexagonal – cancrinite, or cubic – sodalite.     

Pressure shaping of titanium nickelide upon heating under shear stress

A unidirectional variation of the pressure applied to Ti-Ni alloy was found to cause strains of different sign when the material temperature was changed in 10 K steps. The pressure dependence of twin yield stress was obtained. It is concluded that pressure may initiate twinning in crystals.     

The heat-conduction problem for a shell with a system of diathermanous cuts

Using the two-dimensional Fourier transform and the elementary theory of distributions, we solve the heat-conduction problem for shells with a system of diathermanous cuts. We take account of heat exchange according to Newton's law on the lateral surfaces of the shells. For a spherical shell with two cuts of identical length we carry out numerical studies of the influence of the thermophysical properties of one cut on the jump in temperature of the adjacent cut. Three figures. Translated fromTeoreticheskaya i Prikladnaya Mekhanika, No. 25, 1995, pp. 86–89.     

Direct restoration of light amplitude and phase by the reproduced structure of intensity in the Talbot effect

We suggest a technology for restoration of light-beam amplitude and phase on the basis of the Talbot effect. As a result of numerical investigations we found that the determining role in the restoration of fronts is played by the magnitudes of the spreads of the phase front. When the spreads of the phase do not exceed a certain limit, independent highly accurate restoration of both fronts is possible. Admissible limits of the change in the spreads of each of the fronts are determined numerically. Exceeding of these values leads to a sharp decrease in the accuracy of restoration of phase and amplitude. Baltic State Technical University, 1, 1-ya Krasnoarmeiskaya St., St. Petersburg, 198005, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 2, pp. 660–663, September–October, 1997.