Phase-selective synthesis and polymorphic transformation of crystalline red phosphorus.

Recent advances in black phosphorus have renewed interest in elemental phosphorus, sparking a resurgence in the study of its allotropes, especially crystalline red phosphorus (RP). Although progress has been made in synthesizing various crystalline RP phases, current strategies often rely on specific precursor formulations, limiting their scalability for industrial applications. A unified gas-phase method enabling phase-selective synthesis under consistent conditions remains elusive, and the underlying mechanisms governing polymorphic transformations are not yet fully understood. Herein, we achieve the phase-selective synthesis of crystalline RP powders via a solid-phase thermal transformation (STT) method. Extensive experiments were conducted to elucidate the synthetic mechanism of the STT method. The gas-phase molecule-mediated (GPM) solid-solid phase transition model was proposed to describe the synthesis process. Additionally, we demonstrated the sequential transition of Form II-Form IV-Form V RP from both thermodynamic and kinetic perspectives, and clarified the specific structural evolution pathways through first-principles calculations. A theoretical framework based on Ostwald's rule was developed, integrating temperature- and time-controlled methods to guide the polymorphic transformation of crystalline RP. Our work advances the understanding of selective synthesis and phase transitions of phosphorus, laying the foundation for the study of polymorphic transformations in non-metal elements.