Study On Physical Properties Of Co-doped Giant-?' TiO₂ Ceramics

High dielectric materials are widely used in capacitors,memories,filters,resonators and other electronic devices and are the essential factor for the high performance and size miniaturization of electronic devices.However,it is generally a great challenge to obtain materials with giant permittivity,low dielectric loss,good stability for temperature and frequency,high strength of electrical breakdown,and research of high dielectric materials is currently a hot topic worldwide.In a report made by the research group in Australian National University,(Nb,In)co-doped TiO2 dielectric ceramics materials showed the excellent high dielectric properties.The dielectric permittivity can reach 104 orders of magnitude,the dielectric loss can be controlled below 5%,and the high dielectric properties of(Nb,In)co-doped TiO2 ceramics vary little in the temperature range of 80 K to 450 K.They proposed that the high dielectric properties of such materials originate from the electronic pinning-defect dipole-effect.In the subsequent study,a research group in Xi'an Jiaotong University also prepared(Nb,In)co-doped TiO2 ceramics materials and proposed that the high dielectric properties of such materials should originate from the Internal Barrier Layer Capacitance,instead of electronic pinning-defect dipole-effect proposed by the research group of Australian National University.The author's group also studied the(Nb,In)co-doped TiO2 high dielectric ceramics materials where the dielectric ceramic materials with excellent overall performance are successfully prepared.Based on the above results,a series of co-doped TiO2 dielectric ceramics were prepared by modified solid state reaction method.The effects of sintering conditions,annealing and co-doping elements on the dielectric properties were investigated.First,the author prepared some(Nb,In)co-doped TiO2 ceramic samples under different sintering temperature conditions,and systematically investigated the micro structures and dielectric properties.After annealing,the dielectric permittivity is greatly decreased,and the grain boundary resistance is largely increased.Besides,the insulation is improved and the dielectric loss is greatly reduced.The dielectric permittivity is very sensitive to the sintering temperature.The dielectric permittivity is smaller when the sintering temperature is low.When the sintering temperature is 1400?,the dielectric constant can reach a high level,and the dielectric loss can be kept below 5%.However,when the sintering temperature is too high,the dielectric permittivity will be conversely decreased,and the dielectric loss will be increased.The strength of the electrical breakdown of the annealed ceramic samples also reaches a high level.Furthermore,the dielectric properties are of little temperature dependence.It can be said that the sintering temperature and the annealing temperature have an important effect on the dielectric properties.Then,the author studied the effect of tantalum elements on dielectric properties of co-doped TiO2 ceramics.Ceramic samples with compositions of(Sb0.5In0.5)xTi1?xO2,(Ta0.5In0.5)xTi1-xO2 were prepared,where x = 0.01,0.03,0.05 and 0.10,respectively.It was found from the dielectric spectra of annealed ceramic samples that these two kinds of ceramic samples exhibit excellent dielectric properties,when the doping level is low,and the annealing temperature is 780?,which means that the dielectric constant can remain at the level of 104,and the loss can also control below 5%.The measurement of the complex impedance spectrum also shows that the grain boundary resistance is greatly improved after annealing,and the insulation of the ceramic samples has been greatly improved.From the data of I-V curve,it was found that the strength of electrical breakdown of those ceramics with low doping amount conditions can reach the same level as(Nb,In)co-doped TiO2 ceramics.It can be concluded that the(Sb,In)co-doped TiO2,(Ta,In)co-doped TiO2 ceramic material are also a kind of dielectric materials with good overall performance.The author also studied the effect of trivalent elements on dielectric properties of co-doped TiO2 ceramics.Ceramic samples with the compositions of(A0.5Nb0.5)0.01Ti0.99O2 were prepared,where A represents Sm,Gd,Nd and Dy,respectively.By the comparison of the dielectric spectra between the unannealed samples and the annealed samples,it was found that the dielectric permittivity of the annealed samples is decreased and the dielectric loss is decreased too.However the dielectric loss of the annealed samples is still high.Even if the annealing is performed at a comparatively high temperature,the dielectric loss is still about 20%.It was also found that the grain boundary resistance values of the annealed samples with the composition of(A0.5Nb0.5)0.01Ti0.99O2(A= Sm,Gd,Nd,Dy)are lower than those of the(Sb,In)co-doped TiO2and(Ta,In)co-doped TiO2 ceramic samples.