[M-IS23] 結晶成⻑、溶解における界⾯・ナノ現象

[MIS23-P08] マイクロ引き下げ法を用いた四ホウ酸ストロンチウムの化学量論組成近傍での結晶育成

*麻川 明俊¹、町田 貴明¹、稲葉 祥¹、濱田 悠生¹、畝田 廣志¹、小松 隆一¹、北風 嵐¹ (1.山口大学大学院創成科学研究科)

SrB₄O₇ (SBO) has recently received much attention as a wavelength-conversion material that can operate into the deepest ultraviolet wavelengths (125 nm). The utilization of SBO for semiconductor lithography and laser ablation requires fully transparent crystals. Here, we show the growth of SBO crystal fibers with near-stoichiometric composition by the μ-pulling-down method. SrB_2xO_3x+1 ceramics sintered with various values of x were evaluated by X-ray diffraction (XRD). The melting point of the SBO ceramics was measured by differential scanning calorimetry (DSC) as 1017 °C, and the heat of fusion was 63.3 J/g. Figure 1 shows the external form of SBO crystal fibers grown with various x values. Crystal fibers shown in A and C were opaque due to the formation of growth ridges (black arrows). Also, we succeeded in obtaining transparent SBO crystal fibers by the growth with a stoichiometric composition. Then, we observed SBO crystal fibers grown with various x values by polarized optical microscopy. As a result, even when the deviation from stoichiometric composition was ± −0.1 mol % SrO (x = 2 ± 0.004), SrB₂O₄/SrB₆O₁₀ appeared. These results demonstrate that SBO shows no solid-solution width and that the stoichiometric composition is equal to the congruent composition. In contrast, since growth ridges including SrB₂O₄/SrB₆O₁₀ were formed only on surfaces of the SBO single crystals, SBO crystal fibers grown with nonstoichiometric composition were opaque. We could explain the formation of growth ridges via compositional supercooling on rims.