Preparation And Dielectric Properties Of （La+Nb） Co-doped TiO₂ Ceramics Composed Of Submicron-sized Grains

Co-doped TiO₂ceramics have received extensive research attention in recent years,due to their very high permittivity and relatively low dielectric loss.Until now,co-doped TiO₂ceramics have been prepared using various combinations of element doping,grain boundary modification additives,and different processing parameters,with the effect on the dielectric properties of the co-doped TiO₂ceramics being extensively investigated.However,preparation of co-doped TiO₂ceramics using co-doped TiO₂nanoparticles has not been reported in literature.In this work,a sol-gel method was used to synthesize nanometer-sized rutile（La+Nb）co-doped TiO₂powders,which were employed to prepare（La+Nb）co-doped TiO₂ceramics of submicron-sized grains.The specific research content and results are as follows:1.The（La+Nb）co-doped TiO₂powder was prepared by the sol-gel method.The effect of co-doping on the crystal structure and micro-morphology of TiO₂was explored.The anatase phase will completely transform into the rutile phase at 900°C.With the increase of doping concentration,the lattice parameter of TiO₂gradually increases.The prepared powder particles are all nanometer-sized,and as the doping concentration increases,the particle size first decreases and then increases,and it is the smallest when the doping concentration is 3%.2.Dielectric ceramics are successfully prepared by the prepared powder through the process of pressing,sintering,polishing,annealing and other processes.The effect of the（La+Nb）co-doping concentration on the microstructures,valence state changes and dielectric properties of the obtained ceramics was studied in detail.By adjusting the annealing temperature and annealing time,co-doping of La and Nb can significantly increase the dielectric constant of the ceramics,and can also reduce the dielectric loss of the ceramic.For a 2%co-doping concentration,it was found that the（La+Nb）co-doped TiO₂ceramic had dielectric permittivity higher than 2×10⁴for frequency up to 1 MHz and the lowest dielectric loss was 0.019 at 1 k Hz.The average grain size of the（La+Nb）co-doped TiO₂ceramics was less than 200 nm,which is much smaller than that of conventionally solid phase reaction prepared co-doped TiO₂ceramics generally having micron-sized grains.The electron-pinned defect-dipole effect was considered as the main reasons for colossal permittivity and low dielectric loss.3.The dielectric properties of TiO₂ceramics with different doping concentrations at different temperatures were explored.When the temperature is lower than 150°C,the co-doping of La and Nb can effectively improve the dielectric properties of the ceramic,and the temperature stability is better.But when the temperature is higher than 150°C,co-doping will cause the dielectric constant and dielectric loss of the ceramic to increase sharply at the same time,and it cannot effectively improve the dielectric properties of the ceramic.The performance of the sample with 2%doping concentration is still the best.