Investigation into the Processing of Transparent Oxyfluoride Glass and Glass Ceramics Containing CaF2 Nanocrystals in Presence of K2O Additive

During the last few decades، oxyfluoride glass ceramics containing fluoride nanocrystals have received more attention in photonic applications due to their low phonon energies (~500 1/cm) and favorable mechanical، thermal and chemical stability. Main purposes of the present research are investigation of the K2O role on their processing، crystallization behavior structure and transparency. Glasses in the SiO2- Al2O3- CaO- CaF2 system with different amounts of K2O additive (1. 5، 3 and 4. 5 weight ratio) were prepared by convenient melting process. DTA curves exhibited two exothermic peaks، one related to CaF2 crystallization (~ 700 °C) and the other which had not been interpreted clearly before (~ 900°C). XRD patterns، SEM images and EDX analysis confirmed the DTA results and revealed that the second exothermic peak was related to crystallization of anorthite. Glass ceramic samples were prepared on the basis of crystallization temperatures derived from DTA. The only precipitated crystalline phase in the glass samples heat treated on the basis of the first peak of DTA، was CaF2 With the aim of studying the transparency and structural changes of glass samples with different amounts of K2O content، transmittance in UV- Vis region and FT-IR spectra of them were studied. According to the better crystallization behavior and higher transparency in UV- Vis region (~87%)، the glass containing 4. 5 (weight ratio) K2O additive has been introduced as the best basic glass.