X. B. Hu

Growth and properties of K2Al2B2O7 crystal

The flux systems for the growth of crystalline K 2 Al 2 B 2 O 7 (KABO) are discussed. KABO can be grown from both KF and NaF flux by a top-seeded growth method. It is easier to grow the crystal in NaF flux than to do so in KF flux. Seed directions influence the quality and morphology of the KABO crystal. The average thermal expansion coefficients are experimentally determined to be 8.4 × 10 -6 /K, 1.65 × 10 -5 /K along a-axis and c-axis, respectively. The specific heat was measured over a range of temperature 30-295 °C, which is double that of crystalline BBO. Some other data on the chemical and physical properties of KABO are also presented.

The growth defects in self-frequency-doubling laser crystal NdxY1 − xAl3(BO3)4

The growth defects in flux-grown NdxY1 − xAl3(BO3)4 (NYAB) single crystals have been investigated by means of chemical etching and synchrotron radiation techniques. The band-shaped and polysynthetic twins were detected by optical microscopy due to the difference in etching rates between the host crystal and the twin. In the meantime, the orientation and symmetry of the twins were analyzed from their etching patterns. A large number of etch pits with regular shapes were also found on the surface, and these etch pits correspond to outcrops of the dislocations originating from the seed crystal or inclusions.

The formation mechanisms of dislocations and negative crystals in LiB3O5 single crystals

Dislocations and negative crystals in LiB3O5(LBO) single crystals were investigated by white-beam synchrotron radiation topography (WBSRT) and birefringence image. The WBSRT revealed that the grown-in dislocations are mainly pure screw or edge types with the Burgers vectors in the low index directions on the (010) lattice plane. Based on the structure analysis, the cause of the formation of dislocations can be interpreted in terms of the loose packing of B-O rings on the (010) lattice plane. In addition, the negative crystals, which were observed by the birefringence image, tend to present at regular shapes which are similar to that of the host crystal, It is proposed that the negative crystals result from the formation of liquid parent inclusions and the following inward growth.

Theory of twinning structures in the orthorhombic phase of ferroelectric perovskites

The microstructures of coherent , and domain walls in the orthorhombic phase of ferroelectric perovskites have been studied on the basis of Landau - Ginzburg theory for the first-order phase transitions. It is found that for the space profile of the polarization within an uncharged wall layer, the normal component always remains zero or constant, while the component parallel to the wall plane has two kinds of inhomogeneous configuration, one of the `Ising type and the other of the `Bloch type. Quasi-one-dimensional analytic solutions for polarization components, elastic strains, and clamping stresses are obtained for the Ising-type , and wall interfaces. The structural characteristics and physical properties of the Bloch-type walls are also illustrated and discussed. All of the theoretical results are functions of macroscopic quantities for perovskite crystals, and can be applied to real systems when these quantities are obtained from experiments.

Growth defects in Nb:KTP crystals observed by synchrotron radiation topography

Abstract The growth striations, growth sector boundaries and grown-in dislocations in flux-grown Nb-doped KTiOPO 4 crystals have been investigated by white-beam synchrotron radiation topography. The distribution of growth sectors, which mainly consists of {011} and {201} sectors, is clearly shown and characterized, and the effects of growth striations on the non-critical phase matching along the [100] direction are discussed.

Observation of inhomogeneity in congruent LiTaO3 crystal

Abstract 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.

Growth and defects in YbxY1−xAl3(BO3)4 crystals

YbxY1-xAl3(BO3)(4) (x = 0.1, 0.07 and 0) crystals have been grown by the flux method. The growth defects of YbxY1-xAl3(BO3)(4) crystals were detected by X-ray topography. It is found that the perfection of YbYAB crystal with low Yb dopant is better than that with high Yb dopant. In Yb0.1Y0.9Al3(BO3)(4) crystal, growth bands, growth boundaries, grown-in dislocations and inclusions were observed. However, the densities of growth defects for Yb0.07Y0.93Al3(BO3)(4) and YAl3(BO3)(4) are low and no obvious inclusions are observed in these crystals. In addition, growth twins were detected in YbxY1-xAl3(BO3)(4) crystal by using the chemical etching method. It is found that the growth twins occur frequently in Yb0.1Y0.9Al3(BO3)(4) crystal whereas no growth twin appears in YAl3(BO3)(4) crystal. Based on the experimental observations, the formation mechanism of growth twins is discussed. In the meantime, the effective measures for reducing the growth twins and defects are proposed

Image shifts resulting from the misorientation of two individuals in GdCa4O(BO3)(3) crystal

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

Investigation of Optical Inhomogeneities and Growth Defects in Flux‐Grown Nb:KTP Crystals

Optical inhomogeneities and growth defects in flux-grown Nb-doped potassium titanyl phosphate crystals have been investigated. The growth striations, growth sector boundaries and dislocations are revealed by white-beam synchrotron radiation topography. All of the observed dislocations are growth induced and no ferroelectric domains are found in the crystals. It is believed that the main reason for causing the instability of the 90° non-critical phase matching along the 2-direction is related to the growth striations, especially of {011} sectors.

X-ray topographic study of twins in Nd x Y(1−x)Al3(BO3)4 crystal

SummaryThe twins in self-frequency-doubling laser crystal NdxY(1−x)Al3(BO3)4 (NYAB) have been investigated by the transmission synchrotron topography and conventional Lang topography. It has been found that the twins in NYAB are similar to Brazil twins in natural quartz,i.e. the twin element is the mirror plane of typen