Fabrication of nanocrystalline λ-Ti3O5 with tunable terahertz wave transmission properties across a temperature induced phase transition

Abstract

λ-Ti₃O₅ was a newly discovered material with intriguing phase transition characteristics, which exhibits huge potential in the application of memory and tunable optoelectronic devices. However, the fabrication of λ-Ti₃O₅ still presents a great challenge and its application needs further investigation. In this work, we developed a novel method to fabricate nanocrystalline λ-Ti₃O₅ by carbothermal reduction of nano-TiO₂, and explored its terahertz transmission properties through a temperature induced phase transition. A second phase was introduced to inhibit the grain growth of titanium oxide during the carbothermal reduction, by performing a surface modification of the precursor nano-TiO₂ particles with Al₂O₃. This process was proved to be critical for the formation of nanocrystalline λ-Ti₃O₅. An in situ XRD analysis combined with a first-principles calculation based on plane wave DFT indicated that the nanocrystalline λ-Ti₃O₅ exhibited a semimetallic λ phase to metallic α phase transition across a large temperature range. The phase transition was accompanied by continuous, slow and reversible tuning of the terahertz transmission amplitude. This work provides considerable insights into the synthesis of λ-Ti₃O₅ and opens up studies on the applications of λ-Ti₃O₅ in the THz range, such as but not limited to sensors and smart windows.