Study On Magnetic And Dielectric Properties Of Doped Rutile Wide Bandgap Semiconductor

Rutile wide band gap semiconductors have been the focus of research in the field of material physics and condensed matter physics in the past decades.Characteristics of ferromagnetism and colossal permittivity?CP?can be unfolded in rutile TiO₂ and SnO₂ by doping.These novel properties exhibit significantly academic and practical value in the field of electronic device miniaturization and high energy density storage.Doped TiO₂ is one of the earliest and most typical oxide diluted magnetic semiconductors materials.However the ferromagnetism is still controversial,and the roles of Ti³⁺ as well as oxygen vacancy is also an issue.The result of experiment and first principles calculation indicate that the ferromagnetic in Al³⁺/Ga³⁺/In³⁺ doped rutile TiO₂ should be attributed to the modified magnetic polaron consist by doped ion,oxygen vacancy and Ti³⁺.When the oxygen vacancy concentration is very low,the Ti³⁺ around oxygen vacancy will spin antiparallel alignment and won`t be helpful to ferromagnetic.When the oxygen vacancy concentration increase,a ferromagnetic microstructure forms and give a high saturation magnetic moment.Doped Ga<sup>3+</sup> will replace the Ti between two oxygen vacancies and improve the saturation magnetic moment.Doped ions with lager ions radius is helpful to make the electrons into 3d orbit of Ti and get a stronger ferromagnetic.However,In<sup>3+</sup> doped TiO<sub>2</sub> get the smallest saturation magnetic moment although it has the largest ions radius.The doped In<sup>3+</sup> tend to exist in this form “In<sup>3+</sup>-VO+In<sup>3+</sup>” instead of modified magnetic polaron due to its ions radius.Compared to traditional CP materials,?In+Nb?co-doped rutile TiO<sub>2</sub> has attracted much due to its outstanding performance including high permittivity,low dielectric loss and independence on temperature/frequency.However the origin of novel dielectric behavior in co-doped TiO<sub>2</sub> ceramics is still controversial,and the roles of doped irons is also to be thrashed out.The study on these issues is very meaningful to both academic research and the development in new CP materials.Therefore,we explored the dielectric behavior of?In+Nb?co-doped TiO<sub>2</sub> single crystal and ceramics.CP were discovered in both single crystal and ceramics at room temperature,but one dielectric relaxation was obtained in single crystal as well as two dielectric relaxations were discovered in ceramics from the dielectric permittivity dependence on temperature/frequency.Our experiment indicated the dielectric relaxation in single crystal is surface barrier layer capacitor?SBLC?effect.While the dielectric relaxations in ceramics are SBLC and internal barrier layer capacitor?IBLC?effect.In another word,the CP in single crystal should be attributed to SBLC effect and the CP in ceramics should be attributed to SBLC and IBLC effect.In view of that the CP in co-doped TiO<sub>2</sub> ceramics should be attributed to IBLC effect.The study on the dielectric behavior of Alx Nb<sub>0.03</sub>Ti0.97-xO<sub>2</sub> ceramics exhaust the roles of doped cations in CP.The result indicate that Nb5+ doping should be considered as donor doping,the doping make rutile Ti O 2 which is an excellent insulator semi conductive,and then the microstructure inc luding insulating grain boundaries and semiconducting grains was obtained.The microstructure trigger IBLC effect and show CP.The grain boundaries with lower resistance induced by doped Nb5+ also make a high dielectric loss.Al<sup>3+</sup> doping should be considered as acceptor doping which can capture the carriers induced by Nb5+ doping,it will improve the resistance of grain boundaries and reduce the dielectric loss.Doped Al<sup>3+</sup> also can improve the resistance of grain,the CP disappear until Al<sup>3+</sup> doping amount exceeds Nb5+ doping because of the insulating grain.Based on the study on co-doped rutile TiO<sub>2</sub> CP materials,a new CP material was discovered,Al+Nb co-doped SnO<sub>2</sub> ceramics.CP as high as 103 was obtain in the materials and the dielectric loss can be modula ted effectively by change the ratio of Al and Nb.The dielectric loss of Al0.02Nb0.05Sn0.97O2 was just 0.02 at room temperature,and a weak dependence on temperature/frequency was obtained.Just like in co-doped rutile TiO<sub>2</sub>,Nb5+ doping which is donor doping can introduce semiconducting grain and make CP.Doped Al<sup>3+</sup> can effectively reduce the resistance of grain boundaries and make a lower dielectric loss.What`s more,the improving grain resistance due to doped Al³⁺ in SnO₂ also has impact on dielectric loss.The lager grain resistance the frequency where dielectric relaxation happen move toward to low frequency range.It make a dielectric loss peak move into our testing frequency range,and result in a higher dielectric loss.