Analysis of the core in Bi12SiO20 and Bi12GeO20 crystals grown by the czochralski method

Cathodoluminescence and photoluminescence in the core region of Bi12GeO20 and Bi12SiO20 crystals

“…These impurities are present with higher concentrations in the core than outside, as has been demonstrated for the case of Fe. 10 Although these impurities are unintentionally present in starting materials, it is known that they easily diffuse through the crucible wall, and can get incorporated into a nominally pure crystal. This drawback can be avoided when the same crucible is reused at least four times with pure starting material.…”

Simulation of global heat transfer in the Czochralski process for BGO sillenite crystals

“…One of the main problems related with the crystal quality of these compounds is the presence of a central core area, which is column shaped and darker in color compared with the surrounding material in the crystal boule. The analysis of the grown crystals shows that the core is a more strained area compared to the core-free region [1]. This suggests the existence of certain peculiarities in the temperature distribution in the core area during the growth, which, however, have not been revealed in simulations so far.…”

“…4B is rather significant and, in principle, can be responsible for the appearance in this area elevated thermal stresses revealed in Ref. [1]. Table 1; (B) a ¼ 0:03 cm À1 , l ¼ 0:0018 W/cm K; and (C) a ¼ 0:03 cm À1 , l ¼ 0:018 W/cm K.…”

Effect of the shouldering angle on the shape of the solid–liquid interface and temperature fields in sillenite-type crystals growth

“…In this way the appearance of dark core phenomena has been always identified for non-flat interfaces. Experiments 12.181 simulations have shown that when crystals grow with a flat interface there is no dark core formation [7], and for convex or concave interface core phenomena it is even more pronounced with SLI curvature. Dark core has been generally accepted to design regions within the crystal with a high quantity of stresses and defects due to a non-flat interface and its appearance depends on the shape of the crystals (and thus on facets) but not directly with growth direction.…”