W. Piekarczyk

Dissociation processes and crystal growth of gadolinium gallium garnet

Abstract Dissociation reactions of GGG grown by Czochralski technique have been considered. The influence of oxygen pressure on the dissociation products and on oxidation of iridium been calculated. The equilibrium pressure is equal to 1.2 × 10 -2 atm at 2100 K. Crystals grown at equilibrium pressure were free from precipitations and only few dislocations at the edge of crystal were observed.

The growth of rutile (TiO2) single crystals by chemical transport with TeCl4

Abstract Rutile (TiO 2 ) crystals were grown by chemical transport using tellurium tetrachloride as a transport agent. Isometric crystals as well as rhombohedral-shaped plates were obtained. The crystal size exceeded 4 mm; the average dislocation density was about 4 × 10 4 cm -2 . Experimental conditions, rate of transport, morphology and quality of crystals are described. The choice of the transport agent is discussed.

Czochralski growth and structural investigations of La1−xNdxGaO3 solid solution single crystals

Abstract Growth of single crystals in the pseudobinary LaGaO 3 –NdGaO 3 system by the Czochralski method was investigated. It was found that solid solution crystals La 1− x Nd x GaO 3 exist in the whole concentration range. The structure of the crystals was investigated by X-ray diffraction method. It was found that the unit cell volume decreases linearly with increasing Nd concentration in agreement with Vegards law. With increasing Nd concentration x the lattice parameters a and c decrease, whereas b increases. At x =0.32 parameters a and b become equal and the crystal adopts the pseudo-tetragonal structure. The differential thermal analysis proved that the temperature of the first-order phase transition observed in LaGaO 3 at 150°C rises linearly with Nd concentration at the rate of 20.5°C/Nd mol% up to the melting temperature. The segregation coefficients of Nd in LaGaO 3 and La in NdGaO 3 have been found to be k eff (Nd)≈0.77 and k eff (La)≈1.3.

Optical properties and lasing of BaLaGa3O7 single crystals doped with neodymium

Abstract Large single crystals of BaLaGa3O7 containing Nd were prepared by the Czochralski method and studied experimentally by absorption and emission spectroscopy. The dependence of the spectroscopic properties of the crystals on temperature, Nd concentration and light polarization was determined. Room temperature laser action associated with the 4 F 3 2 − 4 I 11 2 transition of Nd3+ was achieved.

Conditions of maintenance of a flat crystal/melt interface during Czochralski growth of bismuth germanium oxide single crystals

Abstract Investigations of Czochralski growth of Bi 12 GeO 20 and Bi 4 Ge 3 O 12 single crystals in crucibles with different diameters and a constant crystal diameter/crucible diameter ratio d D = 0.42 have been carried out. The effect of the change in height of the melt layer in the crucible on the temperature distribution in the melt and on the critical crystal rotation rate at which a flat crystal/melt interface is formed, is determined. The temperature dependences of the viscosity and density of the melts of the two bismuth germanium oxides and the values of their volumetric expansion coefficients are established from separate measurements. After a suitable processing of the experimental results it is shown that they satisfy the general correlation proposed earlier on the basis of model studies for the critical crystal rotation rate and the geometrical and physical parameters of the system crucible-melt-crystal.

The Czochralski growth of BaLaGa3O7 single crystals

Abstract Single crystals of BaLaGa 3 O 7 have been grown by the Czochralski method. Most crystals have been pulled in the 〈001〉 direction. The crystals obtained contain more Ga 2 O 3 and BaO and less La 2 O 3 with respect to the stoichiometric composition. A distinct dependence of the chemical composition on the growth plane orientation has been observed. The composition of the crystals (cylindrical part) which grew on the (001) plane may be expressed by the formula Ba 1.05 La 0.925 Ga 3.025 O 6.975 .

Growth and structural investigations of La1−xPrxGaO3 solid solution single crystals

Growth of single crystals in the pseudobinary LaGaO3-PrGaO3 system by the Czochralski and floating-zone methods was investigated. It has been found that solid solution crystals La1-xPrxGaO3 exist in the whole concentration range x, The segregation coefficients of Pr in LaGaO3 and La in PrGaO3 have been found to be k(eff)(Pr) approximate to 0.84 and k(eff)(La) approximate to 1.19. The structure of the crystals was investigated by X-ray diffraction method. With increasing Pr concentration x, the lattice parameters a and c decrease, whereas b remains almost constant, the volume of the unit-cell decreases. At x = 0.51 parameters a and b become equal and the crystal adopts a pseudo-tetragonal structure. The differential thermal analysis proved that the temperature of the first-order phase transition observed in LaGaO3 at similar to 150 degreesC rises linearly with Pr concentration I at the rate of 13.3 degreesC/Pr mol%

Thermodynamic model of chemical vapour transport and its application to some ternary compounds: I. The model

Abstract A new model of chemical vapour transport constructed exclusively on the basis of thermodynamic quantities is presented. The transport process is considered as a series of consecutive cycles consisting of four following stages: (I) volatilization of the solid(s) in the dissolution zone; (II) migration of the vapour solution to the crystallization zone; (III) deposition of the solid(s) in the crystallization zone; (IV) migration of the vapour solution to the dissolution to the dissolution zone. In stage I, equilibrium exists between solid and gas phase. If the solid volatilizes incongruently, another solid has to appear, and therefore equilibrium between the two solids and the gas phase is established. In stage II, because of temperature change, homogeneous reactions (association, dissociation, etc.) proceed in the vapour. Owing to the reactions, the composition of the gas changes and a new equilibrium state is established between gaseous substances. Since no solids participate in these reactions, the vapour can become a supersaturated vapour solution. The solution can be in labile ot metastable state of equilibrium with some solid which can exist in considered system, but which may not necessarily be the solid (or one of two solids) existing in the dissolution zone. In stage III the solid to be deposited is the one remaining in the labile equilibrium state with the gas phase of the composition established after its arrival into the crystallization zone. In such a case, the supersaturation of the gas phase with regard to the solid to be deposited is higher than the so-called critical supersaturation. The deposition of the first solid causes subsequent changes in the gas phase composition. Thety can shift the labile vapour solution into the region in which another solid is deposited as the next one if the supersaturation of the gas phase with regard to the solid is higher than the critical one, and so on. The deposition proceeds until the equilibrium between the deposited solid and the gas phase is established. If the superstation is lower than the critical one, the deposition of the solid cannot proceed and the gas phase remains a supersaturated metastable vapour solution. Considering the gas phase composition changes in the successive stages of the cycle, one can explain the behaviour of the transport system or determine the preconditions for depositing a solid of desirable composition.

On the conditions of formation of a flat crystal/melt interface during Czochralski growth of single crystals

The effect of some geometrical and physical parameters of the crucible-liquid-crystal system on the shape of the crystal/melt interface during the growth of single crystals by the Czochralski method is studied by physical simulation. The critical rotation rates at which a flat interface is obtained are established for different crystal diameters, model liquid viscosities and temperatures difference between the crucible walls and the crystal. The data obtained are generalized by a relationshhip of dimensionless numbers. This relationship is checked in Czochralski growth of bismuth germanium oxide (Bi12GeO20) single crystals is found to be satisfied in experiments with a high-temperature melt.

Thermodynamic model of chemical vapour transport and its application to some ternary compounds: II. Application of the model to the complex oxides: ZnCr2O4, Y3Fe5O12 and Fe2TiO5

Abstract The transport behaviour of the five transport systems: ZnCr 2 O 4 /Cl 2 , Y 3 Fe 5 O 12 /Cl 2 , Y 3 Fe 5 O 12 /CCl 4 , Fe 2 TiO 5 /Cl 2 and Fe 2 TiO 5 /(5FeCl 3 +Cl 2 ), have been analysed according to the fur-stage model of the CVT. The outcome of the analysis has been compared with the results of experimental investigations of the above systems. In all cases the experimental results are fully consistent with the theoretical predictions.