Kyropoulos Growth and Characterization of Monoclinic α-Bi2B8O15 Single Crystal with Noncentrosymmetric Structure

Monoclinic bismuth-based borate crystal α-Bi2B8O15 was grown by the Kyropoulos method. High resolution X-ray diffraction analysis showed that the full width at half-maximum of the Y plate was about 0.04°...

Mathematical Support of Automatic Power Equalization Systems for Modular Power Source

An algorithm for controlling the modules of a power supply source of vacuum electric furnaces intended for growing artificial monocrystals of leucosapphire according to the Kyropoulos method is considered. Since the modules from which a source with the required capacity is assembled by connecting them in parallel are not exactly identical with one another, and so are the current conducting buses used to interconnect them, a situation may occur in which some of the modules are underloaded, while others are overloaded. Therefore, in addition to stabilizing the total power produced by the source, the automatic control system must minimize the power difference among the modules. An algorithm ensuring balanced operation of the modules is developed, which is based on modeling the processes in an electrical system consisting of power supply modules and current supply buses that take into account their parameters — resistance, inductance, and mutual inductance. The algorithm has been implemented in the MatLab environment. The algorithm testing results have shown that the power difference among the power supply modules is decreased by more than a factor of two.

IDENTIFICATION IN FORM OF STATES SPACE AND INITIAL CONDITIONS IMPACT UPON ITS RESULTS

The aim of the work consists in the reveal of the most stable method of identification, in the reveal of factors influencing the parameter definition result of the melt model during leucosapphire singlecrystal growth by Kyropoulos’ method. Investigation methods are based on an engineering process computer modeling under the assumption that the object of control is an aperiodic link of the second order. The comparison of identification results is carried out through different methods built-in Matlab system, their adequacy is defined by actual processes. As a result of investigations there is obtained a description of an aperiodic link of the second order in the form of states space, an interpretation of results obtained in the form of a time constant of object control is given. It is shown that the engineering process description obtained in the form of states space is adequate, the availability of non-zero initial conditions (non-zero speed of technological parameter changes) has no influence upon an identification process. There are ob-tained dynamic characteristics for a set of experimental data by Process Models and Space State methods. The application of Space State method is recommended.

Bismuth-Based Oxyborate Piezoelectric Crystals: Growth and Electro-Elastic Properties

The non-centrosymmetric bismuth-based oxyborate crystals have been extensively studied for non-linear optical, opto-electric and piezoelectric applications. In this work, single crystal growth and electro-elastic properties of α-BiB3O6 (α-BIBO) and Bi2ZnB2O7 (BZBO) crystals are reported. Centimeter-sized α-BIBO and BZBO crystals were grown by using the Kyropoulos method. High resolution X-ray diffraction tests were performed to assess the crystal quality. The full-width at half-maximum values (FWHM) of the rocking curves were evaluated to be 35.35 arcsec and 47.85 arcsec for α-BIBO and BZBO samples, respectively. Moreover, the electro-elastic properties of α-BIBO and BZBO crystals are discussed and summarized, based on which the radial extensional and the face shear vibration modes were studied for potential acoustic device applications. The radial extensional mode electro-mechanical coupling factors kp were evaluated and found to be 32.0% and 5.5% for α-BIBO and BZBO crystals, respectively. The optimal crystal cuts with face shear mode were designed and found to be (YZt)/−53° (or (YZt)/37° cut) for α-BIBO crystal, and (ZXt)/±45° cut for BZBO crystal, with the largest effective piezoelectric coefficients being in the order of 14.8 pC/N and 8.9 pC/N, respectively.

Numerical study on the effect of additional resistive heating and crystal rotation on sapphire single crystals (Al2O3) grown by the Kyropoulos method

Reduction of melt–crystal interface convexity during Kyropoulos growth of sapphire single crystals through rotation and crucible bottom heating.