Study On The Composition Design, Dielectric Properties And Relaxation Behavior Of High Thermal Stability Co-doped TiO₂ Materials

In order to meet the application requirements of miniaturization and integration of ceramic capacitors in the electronic market,Multi-Layer Ceramic Chip Capacitor(MLCC)are gradually developing to a smaller size and a wider temperature range under the premise of maintaining the original energy storage capacity.It requires that the dielectric material with high dielectric constant,low dielectric loss and good temperature stability is used to fabricate the device.Hence,TiO2-based giant dielectric ceramics with excellent dielectric properties have gradually become a hot research topic in recent years.In this paper,(Ag1/4Nb3/4)0.005Ti0.995O2(ANT00.005)ceramic was prepared by traditional solid phase method as an example to preliminarily explore the preparation process of TiO2-based ceramics.Based on the above preparation process,three kinds of giant dielectric ceramic systems with(Ag1/4Nb3/4)xTi1-xO2(ANTO),(Ag1/4Ta3/4)xTi1-xO2(ATTO)and(Cu1/4Ta3/4)xT1-xO2(CTTO)were successfully achieved.By characterizing the phase structure,microstructure and electrical properties of the samples,the dielectric properties and relaxation behavior were systematically studied and the origin of giant dielectric properties of TiO2-based ceramics was explained.The main conclusions are as follows:1.By studying the effects of sintering temperature,holding time and sintering environment on phase structure,microstructure and dielectric properties of ANT00.005 ceramic,the optimum sintering conditions are determined as follows:sintering temperature for 1330?,holding time for 10 hours in closed environment.The ANT00.005 ceramic with pure rutile phase structure,uniform grain size,high density and excellent dielectric properties(dielectric constant~9410,dielectric loss~0.037,1 kHz)was obtained.It can be found that the increase of sintering temperature and holding time is beneficial to grain growth.However,the dielectric properties of ceramics are deteriorated by the excessive sintering phenomenon with exorbitant sintering temperature and holding time.In addition,the concentration of oxygen vacancies might be the most direct factor affecting the dielectric properties of TiO2-based ceramics.2.Analysis from three aspects of ion radius,electron shell and electronegativity,Ag+,Ta5+or Cu+co-doped TiO2 ceramics were designed respectively,and ANTO,ATTO and CTTO ceramics with a pure rutile phase structure,uniform grain size,clear grain boundary,few pores and high density were successfully prepared by traditional solid-state method.Among the ANTO ceramic systems,the dielectric loss of ANT00.005 and ANTO0.01 ceramics at 1 kHz is 0.040 and 0.050 respectively,which indicates that the introduction of defect structure with electronic pinning is beneficial to obtain the low dielectric loss.Meanwhile,the excellent temperature stability of ANT00.005 and ANTO0.01 ceramics were achieved,meeting the application requirements of X9R and X8R ceramic capacitors respectively.Compared with ANTO ceramics,the incorporation of Ta5+not only helps to reduce the dielectric loss,especially the dielectric loss of ATTO0.01 ceramic is 0.028 at 1 kHz,but also achieves high temperature stability comparable to that of ANTO ceramics.Comparing the dielectric properties of three kinds of ceramics,it can be found that CTT00.005 ceramics have the best dielectric properties.It also has ultra-low dielectric loss(0.028,10 kHz),excellent temperature,bias and time stability.The temperature stability meets the application requirements of X9E ceramic capacitors.This indicates that Cu+ similar to the electronegativity of Ag+ might be oxidized into Cu2+ with more electronegative during sintering.Therefore,it is possible to attract and bind more free electrons to optimize dielectric properties.3.By analyzing dielectric temperature spectrum and element valence state of ANT00.005 ceramic,it is found that there are five dielectric relaxation phenomena in the test temperature range.There are three kinds of low temperature relaxation with DR1(10 K?50 K),DR2(80 K?170 K)and DR3(180 K?270 K)and two high temperature relaxation with DR4(240??320?)and DR5(380 ??600 ?).Combined with literature analysis,it is believed that the dielectric relaxation of DR1 is related to the freezing of the pinned electrons within the defect clusters.The DR2 and DR3 dielectric relaxation might be related to the polarization of the polaron caused by the jump of carriers between the crystal lattices and the interfacial polarization generated by the activation of the point defects associated with oxygen vacancies at the interface,respectively.However,the generation of DR4 and DR5 dielectric relaxation might be related to the ionization and movement of oxygen vacancies under an applied electric field.Based on the exclusion of material electrode effects,the study of dielectric relaxation of ceramics shows that the giant dielectric properties of TiO2-based ceramics originate from the synergistic effect of the electron-pinned defect-dipoles(EPDD)and internal barrier layer capacitance(IBLC).