Morphological stability of solid-liquid interface during melt crystallization of M 1−x R x F2+x solid solutions

Preparation and characterization of strontium fluoride powders activated by neodymium fluoride

“…На монокристаллах фторида стронция (SrF 2 ), активированных неодимом (Nd), получена лазерная генерация, что позволило использовать их для создания активных элементов лазеров с диодной накачкой [9][10][11][12][13]. Коэффициент распределения (k 0 ) Nd при кристаллизации расплава равен 1,74 и существенно от-личается от единицы, что приводит к неоднородному распределению Nd по объему кристалла и потере устойчивости фронта кристаллизации [14,15].…”

Stability of the solid–liquid interface under constitutional undercooling in the crystal growth of TlCl–TlBr and TlBr–TlI solid solutions

“…To resolve this issue, we used an approach similar to that proposed by Kuznetsov and Fedorov [12] and Fedorov et al [23].…”

“…To evaluate the distribution coefficient k of an impurity component (at infinite dilution), one can use the Van't Hoff equation [12,23]:…”

“…One mechanism behind compositional inho mogeneities in the case of directional solidification is constitutional undercooling, which causes the solidliquid interface to become unstable (morphological instability) [9]. As shown earlier [10][11][12][13], in the case of the directional solidification of a molten solid solu tion by the normal mechanism, in the Tiller-Chalm ers approximation (one dimensional model without allowance for the heat of crystallization, density dif ference, surface energy contribution, and distribution coefficient anisotropy) the criterion for stability of the solid-liquid interface under constitutional under cooling has the form GD/R > mΔx, (1) where R is the solidification rate, G is the temperature gradient across the solid-liquid interface, D is the interdiffusion coefficient of the components in the melt, m is the slope of the liquidus line, and Δx = x S -x L is the concentration difference across the solid-liquid interface. This criterion generalizes the well known Tiller criterion to high concentrations of the two com ponents.…”

Synthesis of CaF2–YF3 nanopowders by coprecipitation from aqueos solutions

“…Also, introducing yttrium fluoride into the calcium fluoride crystal lattice causes dramatic changes in its physical properties, including fluoride-ion ionic conductivity, hardness, cleavage and heat conductivity (the latter two parameters decrease significantly) [23,30]. Relatively high yttrium concentrations complicate Ca 1−x Y x F 2+x single crystal growth from the melts due its incongruent melting, and the formation of a cellular substructure [31,32], and local ordering of the formed solid solution [7,12]. Additional increase in the YF 3 content in the CaF 2 -YF 3 system leads to the formation of another berthollide-type variable-composition solid solution at 65-75 mol.…”