Infra-red transmitting glass-ceramics of the As-Ge-Se system nucleated by zirconium selenide

Abstract

The aim of this study was to produce an infra-red transmitting chalcogenide glass-ceramic nucleated by an appropriate nucleant. In order to crystallize chalcogenide glasses in a controlled manner a preliminary series of experiments, in which the metals of group IVB of the periodic table of elements were used as nucleants, showed that zirconium is an effective additive. Studies of glass compositionsxZrSe₂-(100−x) [As_0.1Ge_0.3Se_0.6] indicated that for values ofx 0.25 and 0.50 mol%, glass-ceramics with high thermomechanical properties were produced. By heat treating at 400° C for 15 h, the glass As_0.1Ge_0.3Se_0.6 with 0.25 mol% ZrSe₂ was transformed into a glass-ceramic with a fracture toughness of 0.848 MN m^−3/2, a sag point of 530° C and satisfactory infra-red transmission. X-ray diffraction analysis revealed that the precipitated crystal phase was germanium selenide (GeSe₂). The parasite absorption band with a maximum around 800cm⁻¹ generally present in the infra-red spectra was eliminated by adding 0.1 wt% metallic zirconium. The infra-red transmision and thermomechanical properties for glass-ceramics of compositions with 0.50 mol% ZrSe₂ were poorer than for those with 0.25 mol% ZrSe₂, for the same heat treatment condtions. The kinetics and activation energies of crystallization were studied by means of electron microscopy. The mechanism of controlled crystallization proceeds by the precipitation of crystalline GeSe₂ on the ZrSe₂ nuclei formed by heat treatment of the initial chalcogenide glass supersaturated in ZrSe₂.