Differential thermal analysis has been carried out on AgGaS2 samples in order to investigate the relationship between the superheating of the melt and the supercooling behaviour of the material leading to an improvement of crystal growth conditions. The knowledge gained will be correlated to the crystal growth experiments which had been carried out by using the gradient freezing method.
Authors:G. Dravecz, B. Shackmann, M. Cochez, and M. Ferriol
Thermoanalytical and crystal growth investigations of the ternary system Cs2O-Li2O-Nb2O5 are presented in order to grow stoichiometric LiNbO3 (LN) crystals. Part of the phase diagram is determined and subsolidus phases are identified at room temperature by X-ray
powder diffraction. Among the constituent phases, a new tetragonal cesium lithium niobate phase is assessed. From the Cs2O-Li2O-Nb2O5 system, good quality quasi-stoichiometric LN crystals can be grown.
, optoelectronics in the IR region, and photocatalysis. A considerable effort has been devoted to crystalgrowth control of hierarchical spheroidal crystalline structures of Sb 2 S 3 in solution [ 1 ]. Simple 1D crystalline nanostructures, such as nanorods
The paper deals with a kinetic study of crystal growth in gelatin and agar gels, using a technique based on radioactive tracers.204TlCl,204TlBr,204TlI,60CoC2O4 and60CoH4C4O6 crystals in gels have been obtained. The global kinetic process of appearance of crystals has been found to be made up of two distinct stages: diffusion of the ions in the gel and crystallization, having different rate constants.
Contamination sources of trace elements introduced into silicon crystals grown by the Czochralski technique are investigated:
the signale comparator method in neutron activation analysis is applied to the determination of impurities in a silica crucible
polycrystalline silicon, grown crystals and residual melt. When particular care is taken to avoid contamination during crystal
growth, it is possible to obtain high purity silicon crystals in which impurity contents are almost below the detection limits
of the analytical method.
Authors:P. Malliga, C. Alosious Gonsago, P. Sagayaraj, and A. Joseph Arul Pragasam
The solution was saturated at 35 °C and seed crystals were formed due to spontaneous nucleation. In this process, three drops of hydrogen peroxide were added to the mother solution of glycyl- l -alanine hydrochloride to inhibit
Results of phase transformations, enthalpy released and specific heat of Ge22Se78–xBix(x=0, 4 and 8) chalcogenide glasses, using differential scanning calorimetry (DSC), under non-isothermal condition have been reported and discussed. The glass transition temperature, Tg, is found to increase with an average coordination number and heating rates. Following Gibbs—Dimarzio equation, the calculated values of Tg (i.e. 462.7, 469.7 and 484.4 K) and the experimental values (i.e. 463.1, 467.3 and 484.5 K) increase with Bi concentration. Both values of Tg, at a heating rate of 5 K min–1, are found to be in good agreement. The glass transition activation energy increases i.e. 102±2, 109±3 and 115±8 kJ mol–1 with Bi concentration. The demand for thermal stability has been ensured through the temperature difference Tc–Tg and the enthalpy released during the crystallization process. Below Tg, specific heat has been observed to be temperature independent but highly compositional dependent. The growth kinetic has been investigated using the Kissinger, Ozawa, Matusita and modified JMA equations. Results indicate that the crystallization ability is enhanced, the activation energy of crystallization increases with increasing the Bi content and the crystal growth of these glasses occur in 3 dimensions.
Glasses with the composition Li2O·2SiO2·nTiO2 and Li2O·2SiO2·nZrO2, where n=0, 0.03, 0.062, 0.1, were prepared and the onset and peak temperatures have been determined by DTA. From these characteristic
temperatures, the kinetic parameters describing the nucleation and crystal growth have been obtained by isoconversional methods.
The kinetic parameters have been used for the calculation of nucleation and crystal growth times for individual glasses so
determining the order of glass stability at reheating. The stability of glasses increases with the content of TiO2 or ZrO2 where the increase is higher for ZrO2. Within the concentration range under study, the increase of both times with the metal oxide concentration is quadratic.
It has been discussed that the crystallization kinetics does not obey the Arrhenius law and, therefore, when using the evaluation
methods based on this law, the results should not be extrapolated outside the temperature range of the measurements.