First-principles Investigations On Mecanical Properties And Electronic Structures Of Diverse Pt-M Intermetallics

Platinum?Pt?and its intermetallics compounds Pt-M?M=Al,Si,Ge and Sn?have attracted great interesting and investigation in the scientific research and high-temperature applications fields,semiconductor field,catalyst field and coating material owing to their outstanding properties such as high temperature resistance,good oxidation resistance,resistance to corrosion,conductive good electrical conductivity and low density.By the first-principles calculation based on density functional theory,a systematical investigation of the mechanical properties and electronic structures of transitional metal Pt and Pt-M intermetallics was performed in this dissertation.For Pt and Pt-Al intermetallics compounds,the result of calculated formation enthalpy reproduce the stable phases,low temperature Pt₃ Al,high temperature Pt₂ Al,Pt₅Al₃,?-PtAl,?-Pt₂Al₃,PtAl₂ and PtAl₅.I4/mcm-PtAl₅ is firstly predicted to be stable phase,meanwhile,the calculated phonon spectra demonstrates that it is dynamically stable.The bulk moduli of Pt-Al intermetallics generally enhance with the increasing of Pt concentration.The Pm???m-Pt₃ Al exhibits the maximum values of bulk,shear and Young's modulus among all Pt-Al intermetallics,while PtAl₅ also possesses outstanding shear and Young's modulus among Al-rich phases.Al-3p electrons are delocalized for all Pt-Al intermetallics,while the delocalization of Pt-5d electrons only shows up in Pt-rich phases.Relatively strong hybridization between Al-Al atoms for PtAl₅,and Pt-Al atoms for Pm???m-Pt₃ Al,is crucial to understand their outstanding structural stabilities and mechanical properties.The crystal structure,thermodynamic,mechanical and electronic properties of Pt-IVA?IVA=Si,Ge and Sn?compounds were calculated.We found that Pt-Si,Pt-Ge and Pt-Sn compounds are all thermodynamic and mechanical stable.For the Pt-rich phases,their bulk moduli calculation follow such a sequence: Pt-Si>Pt-Sn>Pt-Ge,otherwise,the bulk moduli of Pt-IVA intermetallics increase linearly with the concentration of Pt;I4/mcm-Pt₃ Si,C2/m-Pt₃ Ge and Pt₃ Sn exhibit the maximum values of bulk modulus,and by their density of states calculation,an obvious pseudogap may be viewed near the Fermi surface illustrating that there are strong orbital hybridization between the Pt-5d orbitals and Si-3p,Ge-4p and Sn-5p orbitals respectively,and strong covalent bonding of Pt-Si,Pt-Ge and Pt-Sn are formed in I4/mcm-Pt₃ Si,C2/m-Pt₃ Ge and Pt₃ Sn crystal structures.Charge density distribution further unraveled that obvious covalent bonding of Pt-Si and PtGe in I4/mcm-Pt₃ Si and C2/m-Pt₃ Ge crystal structure along the c axis,moreover,the Charge density between Pt and Si,Ge and Sn respectively are increase with the increase of Si,Ge and Sn concentration suggesting that their covalent nature of Pt-Si,Pt-Ge and Pt-Sn are gradually increasing with the the increase of Si,Ge and Sn concentration.