Growth dynamics and photoresponse of the Wadsley phase V 6 O 13 crystals

The preparation of a pure phase has long been the key obstacle for the fundamental research and device application of Wadsley vanadium oxides (V n O 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 V 6 O 13 ( n = 6) using a V 2 O 5 precursor film. V 6 O 13 with an atomic flat (00 l ) 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 V 2 O 5 started as synchronization processes for the nucleation of V 6 O 13 . The endothermic melting process provides the main driving force for the rapid growth of V 6 O 13 crystals along the melt/solid interface. The as-prepared V 6 O 13 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 × 10 4 %. 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.