W. J. Liu

X‐ray Topographic Characterization of L‐Arginine Phosphate Monohydrate Crystals

L-arginine phosphate monohydrate (LAP) organic crystals were investigated by X-ray Lang topography. Selected topographs of nearly perfect seeded grown and self-nucleated crystals show that typical defects inside are grown-in and post-growth dislocations, growth sector boundaries, and microbes, while their features are presented and discussed. No structural defects associated to the presence of step bunching on the (100) surface of the crystal have been observed by X-ray topography.

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.

Kosterlitz-Thouless-type metal-insulator transition in two-dimensional layered media with long-range correlated disorder

We study the transport properties of two-dimensional striped media in the x-y plane with disorder that has long-range correlation along the y-direction. This long-range correlation is reflected by a special form of the Fourier transformation of the spatial distribution of the site energies S(k)1/k with k being the wave vector in the y-direction. Using the transfer-matrix method, we show that there is a continuous line of fixed points for >2 indicating that the system undergoes a disorder-driven Kosterlitz-Thouless-type metal-insulator transition.

Contrast of Ferroelastic and Ferroelectric Domains in White-Beam X-ray Topographs

White-beam synchrotron topography has been demonstrated to be well suited for observation of all kinds of ferroelastic and ferroelectric twin domains. It is found that the domains that are misorientated against each other always appear as orientation contrasts in the topographs, while the antiparallel domains with parallel lattices may show different diffraction intensity by the synchrotron-radiation anomalous-scattering effect. Based on the reciprocal-lattice splitting and the diffraction geometry, a general method of determination of the image displacement associated with two misorientated domains is given to explain their orientation contrast. It is also revealed that the anomalous-scattering contrast of antiparallel domains arises from the anomalous-dispersion terms of the noncentrosymmetric atoms in the unit cell of ferroelectric crystals.

Characterization of Growth Defects in Nd:YCa4O(BO3)3 Crystals by Transmission Synchrotron Topography

The growth defects in Nd: YCa 4 O(BO 3 ) 3 (Nd: YCOB) crystals were investigated by transmission synchrotron topography. It was found that growth striations were the primary defects in Nd:YCOB crystals. Grown-in dislocations, mosaic blocks and inclusions were also observed in the crystals. The effect of temperature field on the formation of growth defects in the crystals was 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.

Growth Twinning in Self-Frequency-Doubling Laser Crystal NdxGd1—xAl3(BO3)4 Observed with White-Beam Synchrotron Radiation Topography

The growth twinning in self-frequency-doubling laser crystal NdxGd1-xAl3(BO3)(4) (NGAB) has been observed with white-beam synchrotron radiation topography (WBSRT). It is shown that the growth twinning in flux-grown NGAB crystal is the 180 degrees rotation twin in which the twofold symmetric operation axis is parallel to the [0001] direction and this kind of twinning often shows the black-and-white contrast in X-ray topography. It is believed that the growth twinning in NGAB was induced by growth bands formed during crystal growth.

Metal-insulator transition in anisotropic systems with both diagonal and spin-orientation-dependent off-diagonal disorder

The localization behaviour of the anisotropic extended double-exchange model with both diagonal and spin-orientation-dependent off-diagonal disorder is investigated using the transfer-matrix method. The anisotropy is described by different in-plane and inter-plane hopping integrals. By using a mean-field distribution of the spin orientation, the localization length of electrons is calculated as a function of temperature. It is found that the metal-insulator transition temperature tMIT of the system increases with decreasing degree of anisotropy ?. On the insulating side, the localization length for t close to tMIT varies as . We also calculate the value of ? for various ?-values. The comparison of the results obtained and the experimental measurements for the layered mixed-valence Mn oxides is discussed.

The application of synchrotron radiation techniques to the study of domain structures and their dynamics in ferroic crystals

The recent research work on domain structures and their dynamics in ferroelastic and ferroelectric crystals by white-beam synchrotron radiation topography is summarized. The real-time imaging, fine-beam Laue diffraction, and anomalous-scattering topography were carried out to the study of the domain structures and phase transition in the ferroelastic NdP(5)O(14) and LaP(5)O(14), and ferroelectric KTa(1-x)Nb(x)O(3), (Ba(0.25)Sr(0.75))(0.9)(K(0.5)Na(0.5))(0.2)Nb(2)O(6), and KTiOPO(4) crystals. Some preliminary results are presented and discussed.

STRONG ANISOTROPY OF KTIOPO4 CRYSTALS UNDER AN ELECTRIC FIELD OBSERVED BY SYNCHROTRON RADIATION TOPOGRAPHY

In-situ white-beam synchrotron radiation topographic observations under an electric field have been made on KTiOPO4 family crystals. The investigation shows a strong enhancement of diffracted intensity of hkl reflections (l not equal 0) and the topographic extinction contrast, when the field is applied along the polar axis. Doped and undoped samples with grown-in defects are studied in detail. It is believed that the movement of K+ ions driven by the field leads to a local accumulation of charges and the lattice distortion. All the field-related phenomena appear to be related to the one-dimensional ionic conductance.