Preparation And Colossal Permittivity Of ?In+Nb?-TiO₂ Ceramic

TiO₂-based ceramics are extremely promising colossal dielectric constant materials,which have received a great attention due to its stable dielectric properties over a wide temperature and frequency range.In this paper,rutile TiO₂ ceramics were prepared by solid-phase sintering method.The optimum preparation process was determined and the effects of doping elements on the dielectric properties were investigated as well.The physical mechanism of dielectric response of?In+Nb?-TiO₂?abbr.INTO?ceramics was also studied.The main conclusions are as follows:1.Anatase phase was dominating phase in INTO ceramics in the temperature range of 600-1000 oC.The crystal structure began to transform from anatase to rutile phase when calcine temperature reached 800 oC.A large number rutile phase appeared when it was 1050 oC and INTO ceramics completely transformed into rutile structure at 1150 oC.2.INTO ceramics prepared by cold isostatic pressing with different sintering temperature regime have a large dielectric constant up to 105.The dielectric constant increases with the increase of the sintering time.The dielectric constant was sequentially reduced and the dielectric loss had a great fluctuation when sintered for 10 h.The dielectric constant of each ceramic with different sintering temperature can be stabilized at 105 while the dielectric loss was also stable at only 0.5.3.There were distinct pores in INTO ceramics prepared by dry pressing and its porosity reached to 12.5%.The dielectric constant of the dry-pressed INTO ceramic is only 103 which continues to decrease as the frequency increases and there was a high dielectric loss up to 1.4.On the contrary,the INTO ceramics prepared by cold isostatic pressing not noly had a more compact structure with the porosity of 9.1% but the permittivity can stabilize at 105.Meanwhile,the dielectric loss can be maintained at 0.5.As a consequence,cold-isostatic pressing is more conducive to INTO ceramic dielectric properties.4.The electrons was generated in the TiO₂ lattice that reduced Ti4+ to Ti3+ when Nb element doped into TiO₂,which increased the dielectric constant up to 105.While the In element doped in TiO₂ ceramics had no significant contribution to the dielectric constant,but the dielectric loss of the TiO₂ ceramic can be remarkably reduced to 0.03.Oxygen vacancies were generated when the In element doped in TiO₂,which gave rise to the decrease of the dielectric loss.5.Electrons and oxygen vacancies were generated in the TiO₂ lattice due to the codoping of In and Nb elements.At the same time,various defect particles formed complex defect dipole clusters that lead to low dielectric loss of the INTO ceramic.Besides,the doping of In and Nb elements changes the electrical properties of the grains and grain boundaries in the ceramic,making the grain and grain boundaries become semiconductive state and high resistive state.The effect of the internal barrier layer capacitor?IBLC?formed by the semi-conductive grain and the high resistive grain boundaries was the reason of the colossal dielectric constant of the INTO ceramic.