Growth of potassium tantalate (KTaO3) crystals by directional solidification

Potassium tantalate (KTaO3) crystals were grown by directional solidification from various compositions of K2CO3-Ta2O5 melt. When raw materials with the stoichiometric composition (K2CO3:Ta2O5=50:50 mol%) were used, K6Ta10.8O30 crystallized as the primary phase, indicating that KTaO3 melts incongruently. K6Ta10.8O30 is newly found in the K2CO3-Ta2O5 phase diagram and it is stably synthesized at temperatures above 1200 degrees C. In contrast, KTaO3 crystallized when the ratio of K2CO3 was more than 51.5 mol%. There were three kinds of color in the KTaO3-crystallized portions: milky white, colorless transparent and pale yellow. Based on these results, the phase diagram of the K2CO3-Ta2O5 system around the stoichiometric composition of KTaO3 is proposed. (C) 2013 Elsevier B.V. All rights reserved.JOURNAL OF CRYSTAL GROWTH. 380:39-42 (2013)journal articl

Czochralski-growth of germanium crystals containing high concentrations of oxygen impurities

Oxygen-containing germanium (Ge) single crystals with low density of grown-in dislocations were grown by the Czochralski (CZ) technique from a Ge melt, both with and without a covering by boron oxide (B(2)O(3)) liquid. Interstitially dissolved oxygen concentrations in the crystals were determined by the absorption peak at 855 cm(-1) in the infrared absorption spectra at room temperature. It was found that oxygen concentration in a Ge crystal grown from melt partially or fully covered with B(2)O(3) liquid was about 10(16) cm(-3) and was almost the same as that in a Ge crystal grown without B(2)O(3). Oxygen concentration in a Ge crystal was enhanced to be greater than 10(17) cm(-3) by growing a crystal from a melt fully covered with B(2)O(3); with the addition of germanium oxide powder, the maximum oxygen concentration achieved was 5.5 x 10(17) cm(-3). The effective segregation coefficients of oxygen in the present Ge crystal growth were roughly estimated to be between 1.0 and 1.4.ArticleJOURNAL OF CRYSTAL GROWTH. 312(19):2783-2787 (2010)journal articl