Crystal growth of metal fluorides for CO 2 laser operation I. The necessity of the RAP approach

Abstract

The 10 μm transparency of halides addresses directly its oxide content. The conversion from oxide to fluoride must have Δ G≪0. HF(g) is different from the other hydrogen halides because its Δ G of formation is larger than that of H 2O(g). Decrease in the hydrolysis of RF 3 (R=rare earth) influences the crystal phase stability and the tendency of the crystal to crack. The base-to-acid behavior of +3 rare earths provides quantitative support. HF(g) and RAP (reactive atmosphere process) CF 4(g) formations of YF 3 from Y 2O 3 are given in detail. This indifference to HF(g) is reported also in the congruent growth of CaF 2, SrF 2, and BaF 2. The explanation is seen in ZrF 4, HfF 4, and ThF 4. Although RAP does not use HF(g), it permits the congruent growth of good-quality single crystals with very low H 2O(g) content.