First-Principles Study On Mechanical, Thermodynamic Properties And Doping Of Zirconia

With the rapidly developing of computer technology, Computational Materials Science plays a key role in the research of materials fields. The density functional theory (DFT) based first-principles calculation is the most typical one which has been widely used in chemistry, optics, mechanics, electricity of materials. This method not only can explain the related experimental phenomena from a microscopic point of view, but also can predict the some experimental results to promote the experiment progress.Because of the high temperature tolerance, corrosion resistance, lightweight, good biocompatibility and outstanding mechanical properties, zirconia ceramic materials has wide application. Additionally, the martensitic transformation (t�'m) of ZrO2 crystal have been widely used in the ceramic toughening, especially successfully applied in the Al2O3 ceramic toughening which can obtain the ZTA.In this paper, we have studied the mechanical properties, thermodynamic properties, the second-order phase transition procedure of ZrO2 and the doping toughening on t-ZrO2. The main work is divided into three parts:1. We have studied the structural parameters, mechanical and thermodynamic properties of the five polymorphs of ZrO2, including P21/c、P42/nmc、Fm3m、 Pbca and Pnma structures at ground state by first-principles calculation in combination with the VRH approximation and Debye model. The results have shown the difference among the mechanical and thermodynamic properties of the five polymorphs of ZrO2. And the bulk modulus of Fm3m-ZrO2 is the maximum, the hardness of the Pbca-ZrO2 is the maximum, the Young’s modulus of P42/nmc-ZrO2 is the minimum; the order of the binding force among the atoms of ZrO2 is Fm3m> Pbca> P21/c> Pnma> P42/nmc from the value of the Debye temperature. Additionally, we have owed the distinction for the mechanical and thermodynamic properties of the five structures of ZrO2 to the charge distribution of them.2. We have researched the phase stability, mechanical and thermodynamic properties’variation with the increasing pressure during the second-order phase transition{P21/c �'Pbca �' Pnma) under high pressure by first-principles calculation in combination with the VRH approximation and Debye model. The phase transition pressures are 9.09 GPa and 12.68 GPa, and the each structures are keeping thermodynamic and mechanical stability before the phase transition. With the increasing pressure and phase transition, the mechanical and thermodynamic properties of the five polymorphs of ZrO2 present some certain variation tendencies.3. We have investigated transition metal elements M, including Y, Ce, Hf and Ti doping t-ZrO2 and compared the thermodynamic stability and mechanical properties of MxZr(1-x)O2 with each other to estimate the toughing effects of M by first-principles calculation in combination with the VRH approximation and virtual crystal approximation (VCA). Taking the mechanical and thermodynamic properties of MxZr(1-x)O2 into account, we think the Hf is appropriate for the micro-doping t-ZrO2, Ce is not appropriate for the single-doping t-ZrO2, Y is more appropriate than Ti for doping t-ZrO2 and the range of the doping content is 3～6%mol are beneficial to promote the toughening effect of MxZr(1-x)O2.The results of this paper are of theoretical direction significance in study of the physical properties and the toughening for Al2O3 ceramic.