Preparation of ZrF_4-NaF-BaF_2-LaF_3-YbF_2 Glasses with YbF_2 Substitution for BaF_2 (LaF_3)

摘要

We have prepared glasses and semicrystalline phases with a green color in the systems ZrF_4(53.5)-NaF(20)-BaF_2(20)-LaF_3(6.5 - x)-YbF_2(x) (0 ≤ x ≤ 6.5 mol %) (I) and ZrF_4(53.5)-NaF(20)-BaF_2(20 -x)-LaF_3(6.5)-YbF_2(x) (0 ≤x≤ 20 mol %) (Ⅱ). Thermal analysis results demonstrate that, in both systems, the glass transition temperature of the samples containing ≤3 mol % YbF_2 lies in the range 200-250℃, their heating curves show two or three crystallization events (at 320-340, 380-460, and 415-490℃), and their melting points range from 460 to 490℃. Increasing the YbF_2 content of the glasses to 4 mol % and above (system I) has no effect on their glass transition temperature, reduces the temperature of the first crystallization event from 340 to 305℃, and produces extra peaks in the range 545-600℃, above the major melting peak, which can be accounted for by a nonequilibrium state of the glasses. Ytterbium difluoride substitution for barium difluoride (10 to 20 mol %) (system Ⅱ) leads to the formation of semicrystalline phases and increases the glass-transition (305℃), crystallization (470-515℃), and melting (570-690℃) temperatures. The IR spectra of such samples show, in addition to a so-called "featureless continuum" (～500 cm~(-1)), absorption bands characteristic of the Yb-F bond. Electronic spectra also confirm that the glasses contain both divalent and trivalent ytterbium.