Study On Regulation And Mechanism Of Dielectric Properties Of Nd Doped Ba_0.4Sr_0.6TiO₃ Ceramics

Doping with rare earth elements is an important research direction to improve the dielectric constant of dielectric ceramics.Previous researchers have focused on the effect of the different content of rare earth elements on ceramics,but almost did not consider the"true concentration"of rare earth elements in the ceramic,which is the concentration distribution of the elements.The main purpose of this paper is to design experiments to study the influence of the uniformity of concentration distribution of Nd on the dielectric properties of the ceramics.On this basis,ceramic materials with giant dielectric and low loss will be prepared by co-doping.Then the mechanism of the giant dielectric phenomenon will be studied.In this thesis,Nd doped Ba_0.4Sr_0.6TiO₃ ceramic was selected as study material.When the content of Nd₂O₃ is 0.005 mol,different holding time was used to change the grain sizes and the uniformity of concentration distribution of rare earth element.So the structure characteristics,dielectric properties and electrical characteristics of the dielectric material with two different doping processes can be studied.Exploring the effect of Nd's uniformity of concentration distribution on the dielectric properties of Nd doped Ba_0.4Sr_0.6TiO₃ ceramics with the surface distribution state of Nd.The result showed that,the dielectric constant of 1#Nd-BST increased to the maximum and then decreased,the tendency of 2#Nd-BST was to decrease,and the numerical points of the dielectric constants showed the horizontal symmetry before holding time increased to 6 h.The change of uniformity of concentration distribution index S_H/S_L can be in good agreement with the change law of the dielectric constant.And it can explain the differences of grains'resistance values,ac conductivities and relaxation activation energies of 1#Nd-BST and 2#Nd-BST.The S_H/S_L values of 2#Nd-BST ceramics were generally high.When the holding time was very short,the high concentration area of Nd in 2#Nd-BST content is larger,so the value of S_H/S_L and dielectric constant will be higher.The increase of holding times will lead to grain growth.Corresponding to the high concentration area of Nd at the grain was gradually reduced,SH/SL will reduce.In 1#Nd-BST,the high concentration area of Nd in grains was low when the holding time was 1 h.As prolong the holding time,the growth of grains will lead to aggregation of Nd in some areas,so value of SH/SL increased,so as dielectric constant.Holding time was 6 h or 8 h,the"dilution"effect of the abnormal grain growth can lead to the deterioration of dielectric properties of ceramics with this two doping processes.0.005Nd₂O₃-0.005Al₂O₃-Ba_0.4Sr_0.6TiO₃ ceramics showed giant dielectric phenomena at room temperature.Sintering at 1360?for 1 h,the dielectric constant was the highest?34904?and the dielectric loss was the lowest?0.08667?.Dielectric constants were above 22000 between 25?and 450?.When the frequency was1 kHz,the variation of dielectric constants with temperature was less than±15%from 102?to 426?.The giant dielectric constant is caused by the strong interfacial polarization of grains and grain boundaries from the analysis of impedance spectra and ac conductivity.Study on the effects of different atmosphere heat treatment production,find out the root cause of oxygen vacancies may generate interfacepolarization strong and not the system.Study on the effects of heat treatment in different atmospheres,it was found out that the fundamental cause of strong interface polarization may not generated from oxygen vacancies.Study on the dielectric relaxation behavior at room temperature,the activation energy value is in the range of 0.44⁰.5 eV,which was not derived from the secondary ionization of oxygen but the two doping ions.Study on the influence of different Al³⁺/Nd³⁺on the dielectric properties of the ceramics.When Al³⁺/Nd³⁺=1,the dielectric constant reached a maximum value,and the dielectric loss can be minimum value.Between Al³⁺and Nd³⁺,there are special interactions can increase the system's defects.The free electrons produced by donor doping can be to compensated by the acceptor doping's demand on the electrons,which will reinforce polarization ability of the system and reduce the high dielectric loss brought by the electronic conductance.