Growth dynamics and photoresponse of the Wadsley phase V6O13 crystals

Abstract

The preparation of a pure phase has long been the key obstacle for the fundamental research and device application of Wadsley vanadium oxides (V_nO_2n+1) due to the mixed-valence feature and closeness in thermodynamic phase diagrams. Herein, we demonstrate a melt-assisted pyrolysis process to prepare pure V₆O₁₃ (n = 6) using a V₂O₅ precursor film. V₆O₁₃ with an atomic flat (00l) terrace and length up to a millimeter was prepared on a c-cut sapphire surface. Both ex situ and in situ real-time investigations on the growth process reveal that the melting and decomposition of V₂O₅ started as synchronization processes for the nucleation of V₆O₁₃. The endothermic melting process provides the main driving force for the rapid growth of V₆O₁₃ crystals along the melt/solid interface. The as-prepared V₆O₁₃ crystal sheets show a broadband photoresponse capability (0.4–8.8 μm) with a rise/fall time of 42 ms/50 ms, and the maximum EQE of 5.4 × 10⁴%. Spatial photocurrent imaging reveals that both photoelectric and bolometer effects contribute to the photoresponse. This study offers a feasible and scalable method for the preparation of high quality mix-valence vanadium oxide for future opto-electrical and energy storage devices.