Influence of Ti─O Bonding and Temperature on the Optical Properties of Ultra‐Broadband Low‐Reflectance Ti ₃ O ₅

Abstract Low ultra‐wide band reflection materials are significant because of their applicability to “black” surfaces. Here, a new promising “black” surface Ti 3 O 5 ceramic with semiconductor–metal phase transition has been discovered through experimental demonstration and density functional theory calculation on three types of phases for Ti 3 O 5 at various temperatures. The Ti 3 O 5 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–Ti 3 O 5 and α–Ti 3 O 5 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–Ti 3 O 5 to λ–Ti 3 O 5 and finally to α–Ti 3 O 5 . 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/Ti 3 O 5 /Al 2 O 3 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.