Realistic computer models of amorphous ZrO2:Ta2O5: Structural, optical, and vibrational properties

Amorphous zirconia-alloyed-tantala (ZrO2:Ta2O5) is of interest as a prospective coating material to make the highly reflective mirrors used in gravitational wave detectors. We study the atomic structure of thin films of ZrO2:Ta2O5 by making realistic computer models using force enhanced atomic refinement. The models are, by construction, in agreement with measured x-ray scattering functions. The models made with x-ray scattering data on as-deposited and 800 ??C-annealed samples showed clear structural differences, particularly in their metalmetal correlation. The ratio of corner-shared to edge-shared polyhedra increased as a result of annealing. The electronic band gap and the density of states of ZrO2:Ta2O5 are found to be similar to that of pure Ta2O5 and remained unchanged upon annealing. We used the Hyed-Scuseria-Ernzerhof hybrid functional to estimate the band gap of ZrO2:Ta2O5 to be ??? 4 eV, which is close to the experimental band gap of pure Ta2O5. The refractive indexes calculated from the models were in reasonable agreement with the experiment. Vibrational modes at high frequencies involve highly localized bond stretch modes associated with a corner-shared O atom connecting two metal-oxygen polyhedra.