DFT Calculation And Analysis Of Si-doped Active Oxides

The composite oxides of Si doped RuO2 and IrO2 are significant electrode materials with industrial application value.There are many experimental studies on these composite oxides,but there are no relevant reports on the calculation of Si-doped RuO2 and IrO2.In this paper,reasonable calculation parameters and conditions were set by VASP to investigate and calculate the solid solution materials of Si-doped（Ru1-xSix）O2 and（Ir1-xSix）O2（x=0,0.125,0.25,0.375,0.5,0.625,0.75,0.875,1）.These related data on structures,energy,and electronic structures that are difficult to collect by experiments were obtained,including the crystal structure,energy band,density of states,Bader,charge density,electron localization function,and conductivity of these two kinds of composite oxides,providing a sufficient theoretical foundation for the application of practical composite materials.As a result of the calculation,the lattice parameters of（Ru1-xSix）O2 seriously deviate from Vegard’s law,while the lattice parameters of（Ir1-xSix）O2 slightly deviate.The single-cell volume of the two systems have tendency to conform to the Vegard’s law.Therefore,Si-doped the two type composite oxides of solid solution both causes some distortion in some condition.However,the interaction of Si doped RuO2 is stronger,which has a great influence on the performanceIn the experiment.Ru0.5Si0.5O2/Ti electrodes were prepared by thermal decomposition method in different annealing temperatures.It is confirmed that the high concentrated Si solid solutions are achieved by proper annealing process,meanwhile the composite oxides occur phase separation at higher temperature annealing.After Si doping,the total energy of（Ru1-xSix）O2 and（Ir1-xSix）O2 are relatively increased,indicating that these two composite oxides are not stable.The calculated results are consistent with the results of experiments or reports.Bader,charge density,and electron localization function show that the Ru-O atoms and Ir-O atoms are belong to covalent bonding.However,Si doped are mainly in the form of ions bonding between Si and O.The study of band structure which depicts a metallic character shows that Si highly doped RuO2 and IrO2 materials always maintain the metal characteristics.The density of states suggests that the electrical conductiving hosts originate from the resonance hybridization of Ru-4d,O-2p electrons and Ir-5d,O-2p electrons,along with small amount Si-3p electrons.The descending of electrical conductivity of Si-doped（Ru1-xSix）O2 and（Ir1-xSix）O2 abide by the exponential attenuation trend with increasing Si doped.In the same molar ratio,the electron concentration of IrO2-SiO2 exhibit higher conductivity than RuO2-SiO2 and the conductivity of Si-doped RuO2 decreases more than that of IrO2.In addition,the surface energies and adsorption energies of（110）surface of RuO2 and Ru0.5Si0₅O2 were also calculated in this paper.These two energies increase after Si doping,which indicates that Si doping reduces the surface actvity of electrode.