PbF 2 –TeO 2 glasses and glass–ceramics: a study of physical and optical properties

Some physical and optical properties of x PbF 2 ⋅(100– x )TeO 2 (0 ≤ x ≤ 90 mol%) glasses and glass–ceramics have been studied. Density increases linearly with increasing PbF 2 content up to 70 mol% PbO, then tends to be constant for 70 < PbF 2 ≤ 90 mol%. The molar volume remains constant in the first region then increases for PbF 2 > 70 mol%. The main factor which controls the molar volume is the change in free volume and packing density. There is a limited increase in conductivity with increasing PbF 2 content then it decreases for PbF 2 ≥ 50 mol%. Pb 2+ ions are the main charge carriers. The band gap E g and the linear refractive index n change in an opposite manner where E g increases with increasing PbF 2 content for PbF 2 ≤ 50 mol%, then it decreases sharply for PbF 2 > 70 mol%. For PbF 2 ≤ 50 mol%, the Urbach energy E U decreases then seems to be constant for further additions. Metallization criterion M and molar refractivity R m change in a similar manner to E g and n , respectively.