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Effect of the melt superheat on equiaxed solidification of Al-20 wt% Cu alloy was investigated by in-situ synchrotron radiography at Beijing Synchrotron Radiation Facility. For comparison, the corresponding DSC analysis was also conducted. It was found that the grain size decreased with increasing the melt superheat. The relationship between the final mean grain size and the melt superheat can be expressed as: d = 4919.3 × Δ T - 0.33 . During solidification, the mean grain size increased sharply in the first 70 s, then reached the final grain size gradually. Furthermore, with increasing the melt superheat, the mean nucleation rate increased, which can be attributed to the fact that increasing the melt superheat led to an increase in nucleation undercooling, and the growth rate and the duration of free growth stage decreased. As the melt superheat increased from 100 °C to 160 °C, the mean nucleation rate increased by 78.2% while the mean growth rate only decreased by 19.3%, which indicated that the high mean nucleation rate and the consequent low mean growth rate may be the real reasons for grain refinement. The increased nucleation density caused earlier growth deceleration due to solutal impingement effects.

Synchrotron X-ray radiography was used to in situ study the solute distribution and the dendritic growth during the bottom-up solidification of Sn–50 wt%Pb alloy under a traveling magnetic field (TMF) for the first time. The buoyance driven evolution and motion of the plumes containing Sn-rich melt are directly observed in the solidification front before the application of TMF. A forced melt flow from left to right is induced with the application of TMF, which results in the redistribution of the solute concentration (facilitate the solute transportation and reduce the local fluctuations considerably) and the change of the dendrite morphologies (promote/suppress the growth of the secondary arms, remelting and fragmentation of dendrites). Meanwhile, the concentration variations of Sn around the solidification front are quantitatively analyzed through the extraction of gray level from sequenced X-ray images.

High yield 3-hydroxy benzaldehyde-N-methyl 4-stilbazolium tosylate (3-HBST) was synthesized by optimizing the reaction temperature. High-quality bulk crystals of 3-HBST were grown by slow evaporation technique and spontaneous nucleation method, respectively. The crystal structure of 3-HBST was determined by single crystal X-ray diffraction (XRD) technique and belongs to monoclinic system. The defects of the 3-HBST crystals were observed by the synchrotron radiation X-ray topography. 3-HBST crystal remains stable until 305 °C, with a melting point of 214.1 °C from the TG-DTG and DSC techniques. The dielectric constant of 3-HBST crystal was also studied. The grown crystal had good optical transparency and the optical transmittance was investigated by UV-vis-NIR spectral analysis. Photoluminescence (PL) indicated green emission occurred at 478 nm. Based on the growth technical analysis and performance parameters measurements, 3-HBST crystal was verified to be a promising organic nonlinear optical crystal.

A near-stoichiometric LiNbO 3 (N-SLN) single crystal has been grown by a Czochralski method from a melt of 58.5 mol% Li 2 O composition. The N-SLN single crystal has been studied by white-beam synchrotron radiation topography. Due to the different structure factors between positive and negative domains at the reflection wavelength near the absorption edge of Nb atom, antiparallel 180° domains in N-SLN have been observed by anomalous scattering. The domain boundary is visible by black–white contrast from positive and negative domain and the ratio of | F ( 0 0 0 6 ) | 2 to | F ( 0 0 0 6 ¯ ) | 2 is calculated.

Large 0.92Pb(Zn 1/3 Nb 2/3 )O 3 –0.08PbTiO 3 (0.92PZN–0.08PT) single crystals were grown successfully by the high-temperature solutions method using PbO as flux. The crystal was determined by powder X-ray analysis to have rhombohedral structure. The surface profile and topography of the crystals were investigated by atomic force microscopy and synchrotron radiation white-beam topography, through which defects such as scratches and inclusions were observed. The optical spectra show that the crystals’ absorption edge is 360 nm. The results of ferroelectric hysteresis loops experiments indicated that the ferroelectric parameters including saturation polarization, remnant polarization, and coercive field increased with the highest applied voltages. According to the differential thermal analysis curve, the melting point of 0.92PZN–0.08PT crystals can be found at approximately 1187°C.

Large tetragonal phase (La,Sr)(Al,Ta)O3 (LSAT) crystals used as substrates for growing functional thin-film materials were successfully grown by the Czochralski method using [0 0 1] LaAlO3 rod as seed. The crystal phase was determined by the method of powder X-ray diffraction analysis and the transmission spectrum indicates that the absorption edge of the crystal is at 270 nm while no apparent absorption peaks were found. Through the technique of environmental scanning electron microscopy and synchrotron radiation white-beam topography, the surface topography and defects were characterized, and clear and stable images of twins, micro-cracks, inclusions, grain boundaries, dislocation etch pits, and growth striations in the as-grown LSAT crystals were obtained.

Large GdCa4O(BO3)(3) crystal has been grown by the Czochralski method. The quality of GdCa4O(BO3)(3) crystal was assessed by white-beam synchrotron radiation topography. It has been found that there is a sub-grain boundary in the GdCa4O(BO3)(3) crystal. The boundary divides the large GdCa4O(BO3)(3) crystal into two individuals. Due to the misorientation between the two individuals, the image shifts can be observed in the synchrotron topographs. Based on the misorientation determined by high resolution X-ray diffractometer, the image shifts were calculated for several reflections. The calculations are in agreement with the measurements from the topographs very well. In addition, the formation mechanism of sub-grain boundary is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

The inhomogeneity in a congruent LiTaO 3 crystal has been observed by transmission synchrotron topography. Many extraordinary regions exist in congruent LiTaO 3 crystal and they often show diffraction intensity different from that of ordinary regions in synchrotron topographs. Differential thermal analysis indicates that the Curie temperature of the extraordinary region is lower than that of ordinary region, and the extraordinary region is really a high defect density region. The diffraction contrast of the extraordinary region in synchrotron topographs is explained qualitatively by a calculation at the selected wavelength.