Abstract

Vapor deposited amorphous oxide mixtures of TiO2 and Ta2O5 are used as the high index layer in interference coatings for gravitational wave detectors (GWD). The addition of Ti to Ta2O5 with a cation concentration of ∼25% reduces internal friction when the thin films are annealed at temperatures below the crystallization temperature [1,2]. A similar behavior observed in mixtures of ZrO2 and Ta2O5 was explained as being due to modifications in the bonding of Ta-O polyhedra in which the population of edge- and corner-shared polyhedra decreases and that of corner-shared polyhedra increases [3]. These structural modifications at the medium range, i.e. within a few nanometers, correlate with the reduction of internal friction with annealing.