High-throughput Screening Of Novel MAX Phases

Based on the synthetic classic MAX phase crystal structure,this thesis constructs a series of ternary MAX phases with new elements and new structures.The lowest energy structures of the constructed MAX phase compounds were predicted by high-throughput computing,and the thermodynamic,kinetic and mechanical stable phases of the three systems were screened.Finally,the electrical and mechanical properties of the stable phases were calculated.In M₂AX system,17 effective structures and 300 compounds were constructed.There are 193 M₂AX compounds whose lowest energy structure is the 1 structure of space group 194,accounting for 64.33%of the 300 compounds.A total of 92thermodynamic stable phases were screened,including 44 synthesized phases and 48new phases.Among the 48 new phases,there are 45 dynamic and mechanical stable phases.The structures of the 45 new phases are distributed in two crystal systems（rhombohedral and hexagonal crystal systems）,three space groups（space groups 194,186 and 164）and four structures（structures 1,3,6 and 14）.Among the 45 stable phases,the structures of 35 compounds are consistent with those of the traditional M₂AX phases.All 45 stable phases belong to conductors and the conductivity at the Fermi level is mainly contributed by the d-orbital of the M atoms.And the stable phases have high elastic modulus,hardness and weak machinability,of which 28 phases belong to ductile materials and 17 phases belong to brittle materials.In M₂A₂X system,42 effective structures and 300 compounds were constructed.There are 148 M₂A₂X compounds whose lowest energy structure is the 11 structure of space group 164,accounting for 49.33%of the 300 compounds.A total of 25thermodynamically,kinetically and mechanically stable M₂A₂X phases were screened in this system,including two synthesized phases.The structures of 25 stable phases are distributed in two crystal systems（rhombohedral and hexagonal crystal systems）,two space groups（space groups 194 and 164）and four structures（structures 1,3,11 and 47）.Among the 25 stable phases,the structures of 5 compounds are consistent with those of the synthesized phase Mo₂Ga₂C,and the structural symmetry of 20 compounds is consistent with the synthesized phase Ti₂Au₂C（space group 164）.The 25 stable phases are all conductive,and the conductivity is mainly derived from the d-orbital of the M atoms.The stable phases have low elastic modulus,hardness and strong machining ability,of which 15 kinds of compounds belong to ductile materials,and 10 kinds of compounds belong to brittle materials.In M₃A₂X system,51 effective structures and 240 compounds were constructed.There are 118 M₃A₂X compounds whose lowest energy structure is the 6 structure of space group 194,accounting for 49.17%of the 300 compounds.A total of 15thermodynamically,kinetically and mechanically stable M₃A₂X phases were screened in this system,including three synthesized phases and 12 new phases.The structures of 15stable phases are distributed in two crystal systems（rhombohedral and hexagonal crystal systems）,two space groups（space groups 164 and 194）and two structures（structures 6 and 57）.The structures of 12 compounds are consistent with those of the synthesized M₃A₂X phases.All 15 stable phases are conductors,and the conductivity is mainly derived from the d-orbital of the M atoms.The stable phases have high elastic modulus,hardness and weak machinability.All 15 stable phases belong to brittle materials.Through the thermodynamic comprehensive analysis of the stable phases of the three systems,five M₂AX phases Cr₂Ga C,Hf₂Bi C,Ta₂As C,Ti₂Cd C,V₂Zn C,one M₂A₂X phase Nb₂In₂C,two M₃A₂X phases Nb₃In₂C and Zr₃Pb₂C changed from stable phase to unstable phase.There are 53 figures,19 tables and 102 references.