PbF${}_2$-TeO${}_2$ glasses and glass-ceramics. A study of physical and optical properties

Some physical and optical properties of xPbF${}_2$⋅(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.