Mössbauer and DTA Studies of Semiconducting Potassium Vanadate Glasses Containing Iron

Abstract

Abstract A Mössbauer spectrum of a series of potassium vanadate glasses containing 10 mol% Fe2O3 shows a paramagnetic quadrupole doublet, of which isomer shift proves to be smaller than 0.4 mm s−1 with respect to metallic iron. This indicates that the individual Fe3+ ion is present at the substitutional site of the V5+ (and probably V4+) ion constituting a VO4 tetrahedral unit. An increase in the K2O content of the potassium vanadate glasses results in a continuous decrease in the glass transition temperature (Tg), ranging from 239 to 200 °C, when the K2O content is changed from 5 to 30 mol%. This suggests a decrease in the coordination number of the V5+ (and V4+) ion from 5 to 4 and a formation of nonbridging oxygen atoms in the VO4 and FeO4 tetrahedral units. The formation of nonbridging oxygen atoms in the VO4 and FeO4 units is also estimated from a continuous decrease in the quadrupole splitting, suggesting a decrease in the electric field gradient at the iron nucleus and an increase in the symmetry around the Fe3+ ion. These results lead to the conclusion that the introduction of the alkali oxide (K2O) into the V2O5 results in a structural change of the V5+ (and V4+) ions from VO5 tetragonal pyramid (or trigonal bipyramid) to VO4 tetrahedral units.