Effects Of Fe Doping And O Vacancies On The Magnetic And Optical Properties Of TiO₂ By First-principle

TiO₂ is a widely used semiconductor material with many advantages such as better stability,non-toxicity,corrosion resistance,high efficiency,no pollution,and low price.It has good stability under high pressure and high temperature.At the same time,it is a wide band gap oxide semiconductor material.TiO₂ is widely used in transparent conductive oxides,photocatalysts,optoelectronic devices,and dilute magnetic semiconductors due to its good physical properties.Based on the potential practical application value of TiO₂,the research of TiO₂ semiconductor has become the focus of people's attention.The element of transition metal doping can improve the physical properties of TiO₂.At present,there are some theoretical and experimental studies.However,studies on the magnetic effects of Fe doping and oxygen vacancy co-existing in rutile TiO₂ are still controversial,and there are few reports on the magneto-optical mechanism theory of Fe doping rutile TiO₂ with different valence elements,so it is necessary to conduct in-depth research.In order to solve this problem,the optical,electrical and magnetic properties of Fe doped rutile TiO₂ were calculated by using the CASTEP module of Materials Studio 8.0software and the method of generalized gradient approximation?GGA?plane wave super-soft pseudo potential+U based on density functional theory.In order to study the magnetic source and mechanism of the coexistence of Fe doping and oxygen vacancies in the rutile TiO₂ system,In this paper,four super cell models,Ti₁₅Fe O₃₁,Ti₁₅Fe O₃₀,Ti₁₄Fe₂O₃₁,and Ti₁₄Fe₂O₃₀,Fe replacementing Ti and O vacancies of different proportions coexist rutile TiO₂ system were constructed.The state density distribution,absorption spectrum and magnetic moment of the system are calculated.The different ratios of Fe/Vo are 1:1,1:2,2:1,and 2:2.The magnetic properties of the doping system are significantly different.At a ratio of 2:1,the magnetic moment is the largest among all doping systems,and the Curie temperature is higher than room temperature,which benefits high temperature and high magnetic moment dilute magnetic semiconductors.At a Fe/V_Oratio of 2:2,the Ti₁₄Fe₂O₃₀system produces a half-metallic property of 100%electron spin polarizability.The magnetic source is mainly mediated by the holes generated by Fe doping and O vacancy complexes,thereby causing the spinpolarization double-exchange effect on the electron of Ti-3d orbital atoms near the O vacancy,O-2p electron orbital and Fe-3d electron orbital.At the same doping amount,when the distance of Fe replaces Ti and O vacancy is the next nearest,the formation energy of the doping system is the lowest and the stability of the doping system is the highest.Compared with pure rutile TiO₂ system,the absorption spectrum of Fe and O vacancy doped TiO₂ systems is red-shifted.The effect of Fe doping with different valence states on the magnetic and optical properties of rutile TiO₂ has not been recognized.Therefore,this paper construct six different spacing arrangement models for doping Fe²⁺or Fe³⁺valence states in rutile TiO₂.Then,the electronic structure and magneto-optical properties of the system before and after doping are calculated through geometric optimization.The calculation results show that the formation energy in the oxygen-rich environment is lower than that in the titanium-rich environment under the same system,and the stability is higher.Compared stable structure under both oxygen-rich conditions and titanium-rich conditions.The band gaps of the two doping systems are narrowed,the absorption spectra are red-shifted,and holes or electron capture positions are introduced to reduce the probability of hole-is more remarkable,the electron and hole recombination is slower,the separation is faster,the photo catalytic performance is better,and the semi-metallization is performed.P-type dilute magnetic semiconductor with semi-metallization is very advantageous as a hole injection source.Moreover,ferromagnetic mechanism can be achieved at room temperature.Through the first principles,the mechanism and source of Fe-doped and O vacancies doped rutile TiO₂ system are reasonably explained,which is of guiding significance for the application of Fe-doped rutile TiO₂ as a dilute magnetic semiconductor and photocatalytic material.