Bond-Valence-Driven Model for Highest Infrared-Active Optical Phonon Frequency in Complex Oxides

The highest infrared-active optical phonon frequency (ν_max) is a critical parameter governing infrared optical responses, thermal transport, and photon-phonon interactions in polar crystals. Despite their significance, current predictive methods still face challenges in accuracy, efficiency, and transferability across diverse material systems. We present a robust, physics-informed framework that synergizes bond valence theory with intrinsic crystallographic parameters to predict ν_max accurately. Validated across more than 100 complex oxides and 12 doped material systems, the model achieves exceptional agreement with experimental and first-principles-calculated data. Furthermore, we extend our framework to account for temperature and doping effects, enabling the precise tuning of ν_max through compositional engineering. Our model also shows predictability regarding infrared absorption edges, offering a direct pathway to design infrared-transparent materials with tailored transmission windows. This work provides a universal strategy for accelerating the discovery and optimization of advanced infrared optical materials, with broad applications in thermal management, photonics, and radiative coatings.