Tuesday, April 14, 2020

Nature and spatial distribution of extended defects in Czochralski-grown Ca3RE2(BO3)4 (RE  =  Y, Gd) orthoborate single crystals

Pure and Nd-doped Ca3Y2(BO3)4 and Ca3Gd2(BO3)4 orthoborate (space group Pnma) single crystals are considered for applications as materials for optoelectronics, in particular for ultrafast pulse lasers. In the present work, Czochralski-grown single crystals of such materials were studied. All of them were nearly free of defects such as impurity phases or gas bubble inclusions, previously observed and reported in similar orthoborates. Laboratory high-resolution x-ray diffraction together with synchrotron radiation-based white-beam x-ray topography have been employed as experimental techniques. In this paper we perform for the first time a systematic study of extended defects present in those crystals, including the spatial distribution of the defects. The crystal quality of the studied Ca3RE2(BO3)4 samples is relatively good—the mean values of double-axis rocking-curve full width at half maximum are low enough low (in the order of 32–131 arcsec) and comparable with literature results obtained for other borate crystals. The chemical composition is generally uniform along the samples. The nature of the extended defects is recognized—they are mainly crystal blocks with low misorientation angles  ≤0.06°), micromosaics, dislocations, and crystallographic plane bending. A detailed analysis of the bend for each crystal is presented. Simple criteria for classifying bulk crystals in terms of bending profile are formulated.


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