Synthesis of High-Quality, Large Violet Phosphorus Crystals by Mixed Metal Flux

Among diverse phosphorus allotropes, black phosphorus has been attracting significant attention due to the van der Waals layered structure, anisotropic property, Si-like bandgap, and high carrier mobility. However, it is difficult to apply black phosphorus to practical applications due to its poor ambient stability. Recently, violet phosphorus (VP) has newly emerged as the most stable phosphorus allotropes with similar properties. However, current chemical vapor transport (CVT) technology has limitations of small crystal sizes up to 0.5 mm and low crystal quality. In addition, black phosphorus always exists as a side product in the CVT synthesis of VP. Therefore, the synthesis of pure VP is still challenging owing to the absence of a new synthesis method. Here, we report a mixed metal flux method to synthesize high-quality, large VP crystals. VP crystals up to 5 mm in lateral size are synthesized by mixed tin and bismuth flux at high temperatures, whereas tiny black phosphorus crystals are obtained at low temperatures. It implies that the growth temperature is a key parameter to determine the phase of phosphorus. The full width at half maximum of ~0.14^o is observed in X-ray diffraction, indicating the high crystal quality of the VP crystal. Furthermore, the crystal size can be simply controlled by adjusting the cooling rate in the synthesis process.