Theoretical Study On Structures And Properties Of Binary Y-P And Sc-P Compounds Under High Pressure

Research and development of new materials has always been a frontier research topic in condensed matter physics,chemistry,and materials science.As a basic thermodynamic parameter,pressure can effectively regulate the crystal structure and electronic properties of condensed matter,which becomes an important tool for the discovery of new materials.However,high pressure experiments are often limited by multiple factors such as long development cycle,high cost,and stringent conditions.In contrast,theoretical calculation shows obvious advantages in promoting the research and development of new materials,such as the successful synthesis of high-temperature superconductor hydrogen-rich compounds inspired by theoretical calculations.Since the transition metal elements have abundant valence electrons,its phosphides exhibit physical and chemical properties that are different from the main group metal phosphides,it is expected that yttrium and scandium phosphides can exhibit novel components,diverse structures,and remarkable superconductivity.Therefore,based on the first-principles calculation method and the swarm-intelligence structure prediction method,this paper focuses on exploring the unconventional components,novel structures,and excellent superconductivity of yttrium-phosphorus and scandium-phosphorus binary compounds under high pressure.The main research contents and results are as follows:（1）Theoretical study found a series of stable high-pressure phases of binary yttrium phosphides,and determined their stable range within the pressure range of 0-300 GPa.With the increase of phosphorus content in Y-P compounds,the phosphorus atom shows the diversity of arrangement of isolated anions,dimer,zigzag chain,planar sheet,chain-like network,puckered layer,three-dimensional frame,and wrinkled sheet.Notably,the phosphorus-rich structure YP₂ with the space group of Fd-3m has rare vertex-sharing tetrahedral P₄ units.Further calculation shows that the stable Y-P compounds at high pressure show superconductivity.Interestingly,the superconducting transition temperature of Pm-3m Y₃P increases with increasing pressure and reaches 12.1 K at 300 GPa,which is attributed to the enhancement of low-frequency phonon mode softening.（2）Although the high-pressure phase structures of binary scandium phosphides have been reported,the structures and high-pressure phase diagram of scandium-rich phosphides still need to be further studied.In this paper,we systematically explored the Sc-rich compounds of Sc-P system below 300 GPa,and identified four new high-pressure phases,i.e.,Pbam Sc P,P6/mmm Sc₂P,I4/mmm Sc₃P and Im-3 Sc₃P,which enriched the high-pressure phase diagram of scandium-rich phosphides.Further research shows that these four stable phases have good metallicity.Interestingly,P6/mmm Sc₂P with the same configuration as Mg B₂has a high superconducting critical temperature of 19.8 K.Obviously,I4/mmm Sc₃P exhibits a high superconducting transition temperature of 20.5 K,which is the superconductor with the highest superconducting transition temperature among the existing binary transition metal-rich phosphides.The results of this paper not only increase the diversity of the structure of the transition-metal phosphides,but also deepen the understanding of the electronic and superconducting properties of transition-metal phosphides,and promote in-depth research on potential transition-metal phosphide superconductors.