Molecular dynamics modeling of mechanical loss in amorphous tantala and titania-doped tantala

The mechanical loss (${Q}^{\ensuremath{-}1}$) intrinsic to amorphous oxides is the limiting factor for sensitive, high-precision gravitational wave detectors and optical devices. Recent experimental work suggests that doping amorphous tantala with titania reduces ${Q}^{\ensuremath{-}1}$, however, the physical processes underlying this reduction are unknown. Here, we calculate ${Q}^{\ensuremath{-}1}$ for pure and titania-doped tantala using numerical methods combined with molecular dynamics simulations that have atomic levels of resolution. Our results match experimental trends that titania doping decreases the magnitude of the low-temperature loss peak characteristic of these materials, with 62% titanium cation doping minimizing ${Q}^{\ensuremath{-}1}$ at low temperature. We provide a microscopic explanation for this reduced loss by examining how doping affects the potential energy landscape, strain coupling constant, relaxation time, and other properties of the amorphous materials within the framework of the double-well potential model. Analyzing configurational changes provides an atomic description of the transitions driving mechanical loss at various temperatures in these oxides. These results identify the important parameters contributing to ${Q}^{\ensuremath{-}1}$ that are most affected by doping and provide guidance for how to screen for optimal doping combinations to minimize loss in other materials.