Study On Dielectric Properties Of A-BZN Based Ceramics

Bi2O3-ZnO-Nb2O5（BZN） system has emerged as a good low sintering, high dielectricconstant and low dielectric loss at low frequency ceramic material, which can be cofired withgold, silver and copper, which can be used for MLCC, microwave oscillator, microwave filter,et al. Nevertheless, BZN system not only gets higher dielectric loss at microwave frequency,but also exhibits abvious low-frequency dielectric relaxation phenomena at low temperature（100K-150K）. But so far, the reason why BZN ceramic exhibits low temperature dielectricrelaxation is not completely clear.In this paper, the effect of A-site,（A, O）-site,（A, B）-site and （A or B）-site substitutionon phase structure, crystal chemistry and dielectric properties of α-BZN ceramics wasinvestigated. Besides, dielectric relaxation mechanism was mainly studied for almost everysystem.（1） A-site substitution is that Bi³⁺in A-site respectively substituted by Ca²⁺and Pr³⁺. Theresults indicate that when x≤0.25mol, crystal structure of Bi_1.5-xCa_xZnNb_1.5O₇ceramics wasα-BZN phase; when x≤0.30mol, crystal structure of Bi_1.5-xPr_xZnNb_1.5O₇ceramics was α-BZNphase; Ca²⁺and Pr³⁺substituting Bi³⁺partly all make α-BZN ceramics sintering temperaturehigher, make bulk density, grain size, lattice constant and R（O’-A）decrease, make bond valencesums exampled AV（O’）[Bi₄], AV（O’）[Bi₃Zn], AV（O’）[Bi₂Zn₂] increase; what’s more, therelaxation behavior is obviously observed for both BCZN and BPZN ceramics at varioustemperatures from-190℃to130℃; meanwhile, with the amount ofCa²⁺and Pr³⁺increasing,the peak temperature of dielectric constant is shifted to lower temperature, the temperaturecoefficient of dielectric constant is shifted to more negative values.（2）（A, O）-site substitution is that Bi³⁺in A-site substituted by Ca²⁺and O2-substitutedby F-. What the CaF2substituting is same as Ca²⁺substituting is that CaF2substituting makesα-BZN ceramic have relatively lower bulk density, smaller grain size and lattice constant;What the CaF2substituting is different from Ca²⁺substituting is that CaF2substituting makesthe activation energy of α-BZN based ceramics firstly decrease from0.136779eV to0.104240eV, then secondly increase to0.106895eV for CF2sample.（3）（A, B）-site substitution is that Bi³⁺in A-site substituted by Ca²⁺with same contentand Nb5+, Zn2+in B-site substituted by M4+with different contents(M=Ti⁴⁺, Sn⁴⁺, Zr⁴⁺). Theresults reveal that when x≤0.20mol, crystal structure of （Bi1.4Ca0.1Zn0.5）(Zn_{0.5-（x+0.1）/3}Ti_xNb_{1.5-（2x-0.1）/3})O₇ceramics was α-BZN phase; when x≤0.05mol, the samples ofSn⁴⁺and Zr⁴⁺substituting have the second phase called BiNbO4; the two systems of CS and CZ can get higher activity energy than CT system at relatively low temperature because thepeak temperature of dielectric constant of CS and CZ systems are lower than CT system.（4）（A/B）-site substitution is that Bi³⁺in A-site substituted by Mg²⁺and Zn2+in B-sitesubstituted by Mg²⁺。The results show that when x≤0.05mol, the sample of Mg²⁺substitutingBi³⁺has the second phase; the samples of ZM1, ZM2and ZM4stay α-BZN phase; what theGULP simulation calculate is that Mg²⁺is likely to substitute the ion located on B site, whichcoincides with the changes of XRD; with the amount of Mg²⁺increasing, the peaktemperature of dielectric constant is shifted to higher temperature for both BM and ZMceramics. The differences between BM and ZM are that the activation energy of BM firstlydecreases from0.177105eV of BM1to0.140524of BM2, then increases to0.190506of BM4,while the activation energy of ZM gradually increases from0.075075eV of ZM1to0.657700eV of ZM4.