P. Sveshtarov

The effect of the interface shape on automatic Czochralski weight diameter control system performance

Abstract The theory of the weighing method of automatic Czochralski crystal growth developed by Bardsley et al. is extended to cover the cases of non-flat interface growth. It is shown that including the total meniscus volume and the interface segment area in the model can predict possible normal behaviour in anomalous material crystal growth. i.e. one with non-zero meniscus contact angle and liquid density exceeding solid one.

Growth and physical properties of bismuth titanate crystals

The optimum growth conditions for pulling Bi12TiO20 crystals by the top-seeded flux method from a Bi2O3-TiO2 solution in molar ratio 11:1 have been established. Process parameter influence on the crystallization front shape and the central core formation have been studied. Thermal expansion, elastic and thermoelastic moduli have been measured.

Growth and optical properties of Bi12 SiO20 single crystals doped with first row transition metal and aluminium

Abstract Bi 12 SiO 20 single crystals co-doped with first row transition metals and aluminum were grown from the melt by the Czochralski technique. Optimal growth conditions for optically homogeneous crystals have been established. Dopant molar concentrations in the crystal were determined and segregation coefficients calculated. Transmission spectra were measured in the 0.38–0.85 μm range. It was established that adding Al to the melt bleached the crystals and blue-shifted the entire transmission spectrum. Doping with Cu produced a strong photochromic effect after daylight exposure, changing the crystal color from yellow to red.

The melt level technique of automatic Czochralski crystal growth; basic theory and comparison with the weighing method

Abstract Following an approach developed for the weighing method of automatic control, the current error in radius has been related to the melt level signal via a second order linear differential equation. Effects of melt temperature and pull rate variation have been shown to influence the melt level and the weight signal explicitly and implicitly by the resulting diameter change. The terms containing first and second order derivatives introduce a phase shift between the measured level value and the corresponding derived radius error in a way identical to the weighing method of control.

The growth and optical properties of doped bismuth titanate

Abstract The growth conditions for producing Al, Mn, Cr and Al+Cr doped Bi 12 TiO 20 crystals have been studied. Transmission spectra of various crystals have been measured and the absorption has been determined in the range 0.4 – 0.85 μm. A blue shift in the spectral absorption of Al doped Bi 12 TiO 20 and a red shift in Mn, Cr and Al+Cr doped Bi 12 TiO 20 has been observed as compared to undoped material. In Al+Cr doped crystals the absorption is blue-shifted as compared to Cr-only doping.

Growth of α-mercury iodide crystals and study of space charge relaxation in an applied electric field

Abstract Some results on growth by the Temperature Oscillation Method and characterization of undoped and doped α-HgI 2 crystals are presented. Polarization and depolarization time of specimens fabricated from material grown in excess vapour pressure of one constituent component or a dopant have been measured. It is established that crystals grown at excess I 2 pressure show the highest structural perfection and lowest polarization time.

Optical absorption properties of PB5GEO4(VO4)2 single crystals

Abstract Thermal and pulling conditions have been optimized in a laboratory Czochralski apparatus to yield optically homogeneous crystals of hexagonal Pb 5 GeO 4 (VO 4 ) 2 . The wavelength dependence of absorption coefficient was calculated from transmission and reflection measurements in the visible region. A hypothesis regarding the zone structure in connection to the fundamental absorption edge was raised and the bandgap width corresponding to indirect transition at room temperature was determined from the α 1 2 -hv curve.