Density Functional Theory Studies Of M(001)/BaTiO₃(001)(M=Ag,Pd,Ni) Interfece

Barium titanate is a kind of perovskite ceramic oxide.Because of its exceptional piezoelectric and ferroelectric properties,it is widely used in condensed matter physics and electronic ceramic industry,which is known as "the pillar of electronic ceramic industry".In addition,it is also widely involved in optical absorption catalysis,energy information storage,nonlinear optics and other related fields.Although the photoelectromagnetic propertie of barium titanate is excellent,limited by its crystal structure,its mechanical properties have limited its application.Adding ductile materials into BaTiO3 matrix can improve the mechanical properties of brittle ceramics and dielectric properties,which is conducive to the miniaturization of multilayer ceramic capacitor(MLCC).Ag and Pd can be sintered with dielectric ceramics in air without oxidation risk,so they are the most commonly used electrode materials for precious metal electrode(PME)multilayer ceramic capacitor;Ni is a typical inner electrode material for multilayer ceramic capacitor in base metal electrode(BME)because of its low cost.The enhancement of mechanical properties and dielectric properties after the introduction of the metal phase into barium titanate is closely related to the interface.At the same time,interface is usually the weak part of heterogeneous materials,and it is also the only way of stress transfer.During the installation and use,cracks will occur due to thermal stress and other reasons,resulting in product failure.The current research on the M/BaTiO3(M=metal)interface mainly focuses on the experimental aspect,and the theoretical exploration also focuses on the exploration of electromagnetic properties.In order to deeply understand the properties of M/BaTiO3 interface,it is imperative to comprehend the stacking form and electronic structure between BaTiO3 and metal M,and to analyze the initial interaction and thermodynamic stability of the whole M/BaTiO3 interface.Based on the above situation,the Ag/BaTiO3 interface,Pd/BaTiO3 interface and Ni/BaTiO3 interface are calculated in this study based on density functional theory calculation method,which can help people understand the interaction of M/BaTiO3 interface and provide theoretical guidance for the experiment and production of cermet composites.The main contents of this paper are as follows:(1)Six stacking models of Ag(001)/BaTiO3(001)interface are established.After optimizing the surface,the atoms all move to the bulk phase to varying degrees,and the degree of movement is related to the position and type of the atom.The interface(M 22)composed of TiO2-terminated BaTiO3(001)and Ag has the smallest interfacial distance and the largest adhesion work,the smallest interfacial energy and the largest interfacial fracture toughness,and the highest thermodynamic stability.The analysis of electron density difference and partial density of state(PDOS)of the M 22 equilibrium interface shows that the Ag atom and O atom at the interface form a covalent bond.(2)After the optimization of Pd(001)surface,the stacking models of Ag(001)/BaTiO3(001)interface are established considering different BaTiO3 terminated and atom stacking positions.During the surface optimization,it is found that the surface atoms relax towards the bulk,and the degree of relaxation is related to the atomic position.After calculating the interfacial adhesion work,interface energy and electronic structure,it is found that the PV and PVI interfaces formed by the stacking of TiO2-terminated BaTiO3(001)have stronger thermodynamic stability,especially PV has the smallest interfacial spacing,the largest adhesion work,the smallest interfacial energy and the largest interfacial fracture toughness.The electron density difference and partial density of state analysis of the interface show that the Pd-4s/4p orbital of the Pd atom and the O-2s/2p orbital of the O atom are hybridized in many places,which tends to form covalent bonds.(3)The interface of Ni(001)/BaTiO3(001)is studied comprehensively,and interface models are established considering the surface terminated and the stacking position of Ni atoms.After complete relaxation,the interface stability,electron density difference,density of states and overlap population are calculated.TiO2-terminated O-top stacking model has the most stable structure,the maximum adhesion work and the minimum interface energy,and its interface fracture toughness is predicted to be 1.23?1.75 MPa·m1/2 theoretically.The interface bonding is the ionic bond mainly formed by the hybridization of Ni-3d/4s orbital and O-2s/2p orbital.The thermodynamic stability of TiO2-terminated O-bridge stacking model is second only to that of TiO2-terminated O-top stacking model,and its interface fracture toughness is predicted to be 0.94?1.33 MPa·m1/2 theoretically.The Ni—O ionic bond is formed at the interface.