Computational Research On The Structure And Superconductivity Of Ti-PH And Other Ternary Compounds Under High Pressure

Scientists have been exploring high temperature superconducting materials.Recently,hydrogen rich compounds have become a hotspot as candidates for a new class of high T_c superconductors.The purpose of theoretical calculation and prediction is to find stable materials with low pressure and high critical transition temperature?T_c?,and provide theoretical information for the experimental discovery of high-T_c superconducting materials.In this thesis,the structures and superconductivity of the ternary systems of TiPH_n?n=1-8?and TiPB₄ under high pressure were studied.The genetic algorithm?GA?was applied to search for the structures of TiPH_1-8 and TiPB₄ systems,and density functional theory?DFT?calculations were used to study the superconductivity of these systems.The main contents include the calculated results of TiPH_1-8 structures and corresponding T_c's.Due to the high affinity of Ti for hydrogen,Ti-H compounds have good stability.Therefore,we add Ti to the P-H compounds to solve the problem of poor thermodynamic stability of the P-H compounds.The results show that TiPH₄ and TiPH₈have high T_c values and good stability,and solve the instability problem of phosphohydrides.TiPH and TiPH₄ are most stable at 50-200 and 250-300 GPA,respectively.The predicted T_c values of the R-3m-TiPH₄ structure are 51.57 and 62.36 K at 100 and 250 GPa,respectively.The T_c value of the TiPH₈-C/2m structure is 66.67 K at250 GPa.Also,they have both good thermodynamic stability and large Young's modulus,indicating that their syntheses are possible.In addition,we calculated the structures and properties of APH₄?A=Na,Mg,Al and S?systems.The calculation of the ternary hydride APH₄?A=Na,Mg,Al and S?shows that they have thermodynamic and kinetic stability.The most stable structures are NaPH₄-C2/m,MgPH₄-Cm,and AlPH₄-R3m,respectively.Among them,NaPH₄-C2/m and AlPH₄-R3m have not metallic properties within the pressure range studied.Compared with TiPH_n systems,APH₄?A=Na,Mg,Al and S?systems lack good superconductivity.In addition,we try to replace the H element in TiPH₄ with B,and calculate and predict the structure and properties of tipb4.The results show that the thermodynamics and dynamics of tipb4 are stable,the most stable structure is p4mm structure at 250 GPA,but the superconducting critical transition temperature is only?0.94 K.