Gadolinium calcium oxide borate GdCa₄O(BO₃)₃ (GdCOB) crystals have monoclinic, noncentrosymmetric symmetry, and, therefore, exhibit nonlinear effects.

The GdCOB melts congruently and can be grown by the Czochralski method. Single crystals with diameters up to 35 mm and lengths up to 50 mm were grown, from the stoichiometric ratio of Gd₂O₃, CaCO₃ and B₂O₃. The powders were prepared by solid - state reaction. The crystals were grown in nitrogen atmosphere from a 100 mm dia. iridium crucible using the [010] –oriented seed. The pulling rate was in the range of 0,8 – 1 mm/h, and the rotation speed was adjusted to 20 rpm.

Recently by X-ray Lang projection topography in transmission and back reflection geometry we have revealed some structural defects in GdCOB. Density of these defects change along the sample and a core, which is situated in the central part of the sample. In the core density was found to be the lowest [1].

In order to find the nature of this core we used Rocking Curve Imaging (RCI) techniques based on high-resolution diffraction method [2]. That allows us to obtain quantitative information on crystallographic misorientations and lattice quality of large sample area with high spatial resolution.

The sample was cut perpendicularly to the crystal growth direction. We discovered a certain inhomogenity of lattice constants. 2D strain maps were analyzed, and the excess strains in out of the core region respect to the central part of the sample were evaluated to be of the order 5x10^-5. These strains generate spatial deformations in the crystal in lattice in the core region. Fluctuations in spatial distributions of Bragg angle out of the core region were also discovered. This can be attributed to the segregation of crystal components during the growth process.

1. E.Wierzbicka, A.Kłos, M.Lefeld-Sosnowska and A.Pajączkowska, Phys. Stat. Sol. (a) 203 (2) (2006) 220-226

2. J.Z.Domagala, Z.R. Zytkiewicz , I. Grzegory, M. Leszczynski, J.M Yi., J.H. Je, XTOP 2006, 8th Biennial Conference on High Resolution X-Ray Diffraction and Imaging, Baden-Baden, Germany, 18-09-2006, Abstract book p. 111