Properties of chlorofluorozirconate glasses

The effect on selected optical and physical properties of a fluoride glass doped with chloride was investigated. Four compositions were studied: 50%ZrF 4-30%BaF 2-5%ThF 4-3%LaF 3-12%Ab where A = NaCl, NaF, RbCl or RbF. The chlorine addition decreased the multiphonon absorption and its magnitude was determined to be dependent upon the molar concentration of ZrF bonds. The electronic absorption showed a substantial increase into the visible region. The index of refraction was increased by approximately 1.5% due to the more polarizable chlorine ion. There was a substantial change in the thermal stability of the glasses according to differential scanning calorimetric (DSC) analysis. The RbCl composition exhibited the largest ( T x− T g) of 110°C whereas the RbF composition has the smallest value of 68°C. The chloride substitution increased the thermal expansion coefficient very slightly in the Na-containing glasses ( Δα ≈ 2 × 10 −6) and not at all in the Rb-containing glasses. However, the chloride containing glasses were found to be less chemically durable in water due to the higher solubility of chloride as compared with fluoride. These modifications in properties demonstrate the feasibility of a chlorofluoride core/fluoride clad fiber optic with high thermal stability, extended IR transparency, and large numerical aperture.