Influence of Ti─O Bonding and Temperature on the Optical Properties of Ultra-Broadband Low-Reflectance Ti3O5

Abstract

Low ultra-wide band reflection materials are significant because of their applicability to “black” surfaces. Here, a new promising “black” surface Ti₃O₅ ceramic with semiconductor–metal phase transition has been discovered through experimental demonstration and density functional theory calculation on three types of phases for Ti₃O₅ at various temperatures. The Ti₃O₅ ceramic displayed low and temperature-dependent reflectivity in the ultra-wideband. It is made by carbothermal reduction, appearing as a reversible semiconductor–metal transition in β–Ti₃O₅ and α–Ti₃O₅ when heated from room temperature to 220°C. The observed temperature-dependent tunability in terms of ultra-broadband low-reflectivity (0.25–16.0 µm) arises from sequential phase transitions from β–Ti₃O₅ to λ–Ti₃O₅ and finally to α–Ti₃O₅. Additionally, the mechanism of the Ti─O bond for temperature-dependent emissivity is proposed by combining the orbital characteristics of the density of states and phononic structures. Furthermore, a composite PE/Ti₃O₅/Al₂O₃ exhibited 37% reduced solar absorptivity while maintaining high infrared emissivity (∼0.92), confirming Ti-O bonds dominate emissivity properties rather than structural modifications. This work will guide selecting and preparing “black” surface Ti3O5 material toward the desired wavelength-selectable emissivity to satisfy numerous applications.