Research On The High-pressure Structure And Superconductivity Of Yttrium Hydrogen Compounds

In this paper,the genetic algorithm and the first-principles calculations are used to investigate the crystal structures and the superconducting properties of YH_n.The prediction of high-pressure structures of the Y-H compound system are carried out.The most stable structures of YH₃,YH₄,YH₅,YH₇,etc.at high pressures are obtained.Simultaneously,the density of states,thermodynamic stability,dynamic stability,and electron-phonon coupling,superconducting properties for each structures are calculated and analyzed.At the pressure of 200 GPa,the two most stable structures for YH₃ have space group symmetries of P21/m and I4/mmm.The predicted superconducting temperature of the P21/m phase at the pressure of 120 GPa reaches 19 K,while at the pressure of 200 GPa the superconducting temperature was 9 K,however,the superconducting temperatures of other space groups of the YH₃ structures are all 0 K.The frequency,phonon split-state density,and superconducting temperatures for I4/mmm-YH₃ and I4/mmm-YH₄ are compared at120 GPa.We find that the YH₄ structure has a higher superconducting temperature than the YH₃ structure.The calculated superconducting temperature for I4/mmm-YH₄ at 120 GPa is 94 K,and 55 K at 200 GPa.We have further predicted the structures of YH₅ and YH₇ and investigated their superconducting properties.Our calculations show that P4/nmm-YH₅ and P21/m-YH₇ are the most stable structures,and P21/m-YH₅ and Cmcm-YH₇ are metastable structures.The superconducting temperature calculation results show that the superconducting temperatures of P4/nmm-YH₅ and P21/m-YH₅ at 120 GPa are 104 K and 109 K,respectively,while the superconducting temperatures of P21/m-YH₇ at 12 0GPa and 200GPa reach 112 K and 146 K.Moreover,the structures of YH_n?n=2,6,8?at high pressures have also been investigated.Our work reveals that the Y-H system is a highly promising superconductor and has certain theoretical and practical research value.