V.A. Borodin

Local shaping technique and new growth apparatus for complex sapphire products

Abstract The “local shaping technique” is one of the many versions of the Stepanov method. In contrast to the conventional Stepanov technique, in this process, the die forms only an element of the predetermined cross-section of the crystal being pulled, while the whole cross-section is obtained by means of crystal rotation. The growth of sapphire tubes by this technique is described in detail. The stability of the process is analyzed, and the structure of grown tubes is studied. A new growth technique has been developed to obtain complex sapphire products, with continous alteration of the side surface shape. The growth of cone-shaped tubes, hollow cones, and other shapes is described.

Variable shaping growth of refractory oxide shaped crystals

Abstract The paper presents results on growth of refractory oxide shaped crystals by a new method which enables one to vary the configuration of a crystal cross-section during the crystallization process. The field of application of these princially new products is also discussed.

Influence of growth process parameters on weight sensor readings in the Stepanov (EFG) technique

Weight sensors are widely used in automated control systems for growing crystals from the melt by Czochralski technique. They measure a growing crystal weight, a meniscus weight and a force of the surface tension. In order to accomplish an automated crystal growth process by the Stepanov (EFG) technique we studied the influence of the growth process parameters on the force sensor readings. The parameters analyzed were: the pulling rate, the height of the die edges above the melt pool, the power of heating. The dependence of sensor readings on the pulling rate has been examined when a crystal was grown in the form of a tube from dies with various lengths of capillary channels.

Development of the Stepanov (edge-defined film-fed growth) method: variable shaping technique and local dynamic shaping technique

Detailed description of the crystal growth methods permitting one to obtain complicated shape crystals from the melt is given. The variable shaping technique allows growth of crystals with a discrete altering cross-section configuration during crystallization. The local dynamic shaping technique enables one to grow crystals with a continuous alteration of the lateral surface profile by a preset program.

The effect of the solidification front shape on the temperature distribution in the crystal

Abstract The effect of the solid-liquid interface shape on the temperature distribution in a crystal grown from the melt is investigated. The distribution of axial temperature gradients in a growing crystal is obtained by solving the steady state equation of thermal conduction using a computer and from experimental measurements in NaCl crystals pulled from the melt by the Czochralski method. The presence of an axial gradient maximum in the crystal with a convex-towards-the-melt solid-liquid interface and a monotonous decrease of ∂ T ( r, z )/∂ z | r = 0 from a maximal value on the interface boundary is shown to be due to the direction of heat flows and the shape of isotherms whose geometry depends on the heat loss from the side crystal surface. An analysis is carried out of the effect of the phenomena observed on the magnitude of thermal stresses arising in the crystal. The results obtained suggest that the case of a convex-towards-the-melt solid-liquid interface is the least advantageous to grow crystals with a low defect density.

Low Temperature X-Ray Analysis and Electron Microscopy of a New Family of Superconducting Materials

Recent findings in the field of high temperature superconductivity 1 requirte that structural aspects of the behaviour of this class of materials be investigated in detail in a wide temperature interval. A series of superconducting ceramics on the base of lanthanum and yttrium oxides have been obtained in the solid state Physics Institute of the Academy of Sciences of the USSR. This paper presents the results of the analysis of powder and sintered materials, using X-ray diffractometers (DRON), scanning electron microscope and special devices, enabling the investigations to be carried out within 4.2 K-573 K.

Point Contact Study of Metal Oxide Superconductor Y-Ba-Cu-O

High quality tunneling junctions made of superconductors 1 and pure point contacts made of normal metals 2 are perfect objects for investigations allowing one to obtain some quantitative information about the superconducting energy gap Δ (ω) and to restore the function of the electron-phonon interaction α2(ω)F(ω), where α2(ω) is the square of the electron-phonon interaction matrix element, F(ω) is the density of phonon states. These two experimentally observable values are of great importance from the point of view of the origin of superconductivity in now existing compounds and today they receive high priority in connection with the discovery of high-Tc superconductors La-Sr-Cu-O, Y-Ba-Cu-O 3,4. It is still difficult to obtain perfect tunneling junctions and pure point contacts from these compounds because in reality tunneling junctions have short-circuits and point contacts have contaminations in the contact region. The BTK theory 5 (Blonder, Timkham, Klapwijk) describes a transition from the tunneling contact to a metal-like one in superconductor - constriction - normal metal structures ScN. In the present work the point contacts of ceramics with aluminium, copper, lead heterocontacts and of ceramics Y-Ba-Cu-O monocontacts have been studied.