Study On Structure And Dielectric Properties Of ?-BZN Based Ceramics

Bi-based cubic pyrochlore ceramics??-BZN?were prepared by conventional solid state reaction.The microstructure,crystal chemistry and dielectric properties of Bi_1.5Zn₁₊x Nb_1.5O_7+x and(Bi_1.5Zn_0.5-x Mx)(Nb_1.5Zn_0.5)O₇(M= Ca²⁺,Sr²⁺,Ba²⁺and Cd²⁺)ceramics were measured and discussed.The anti-site defects in ?-BZN ceramics were simulated and calculated.1.The microstructure,crystal chemistry and dielectric properties ofBi_1.5Zn₁₊x Nb_1.5O_7+x ceramics investigated.The ceramics were a cubic pyrochlore structure when x?0.015 mol and the second phase occurred at x=0.02 mol.With the content of Zn O increasing,the lattice constant and the bond length R_?A-O'?,R_?B-O?increased,the bond valance sum AV?O'?[A4] and AV?O?[A₂B₂] decreased.The oxygen coordinate ? of 48f?O?gradually decreased,the [BO6]octahedrons became more regular and the coordinate hexahedrons of A site ions with six48f?O?s and two 8b?O'?s became more distortion.Meanwhile,the dielectric constant and the dielectric loss gradually increased.Typical dielectric relaxation was observed at low temperature and the degree of dielectric relaxation decreased with the increase of Zn O.The Tm shifted to lower temperature?x?0.015?and the activation energy Ea in low temperature increased with the increase of x.2.The microstructure,crystal chemistry and dielectric properties of(Bi_1.5Zn_0.5-x Mx)(Nb_1.5Zn_0.5)O₇(M= Ca²⁺,Sr²⁺,Ba²⁺and Cd²⁺)ceramics investigated.All the ceramics were a cubic pyrochlore structure?x?0.1 mol?.With the content of substitution increasing,the lattice constants and the bond length R?A-O'?,R?B-O?increased,the bond valance sum AV?O'?[A₄] and AV?O?[A₂B₂] decreased.The oxygen coordinate ? of 48f?O?gradually decreased,the [BO₆] octahedrons became more regular and the coordinate hexahedrons of A site ions with six 48f?O?s and two 8b?O'?s became more distortion.Meanwhile,the dielectric constant and the dielectric loss gradually increased.The dielectric constant increased with the increase of Ca²⁺,Sr²⁺ and Cd²⁺and decreased with the increase of Ba²⁺.Typical dielectric relaxation was observed at low temperature and the degree of dielectric relaxation decreased with the increasing substitution.The Tm shifted to lower temperature and the activation energy Ea in low temperature increased(except for the substitution of Ba²⁺,the Ea decreased)with the increase of x.3.The anti-site defects in ?-BZN ceramics were simulated and calculated.The result of substitution energy calculation revealed that,the substitution energy of Nb substituted Bi was lower.According to the calculation of Binding energy,the anti-site defects preferred to array along the axis direction and the Frankel defect of oxygen ions was likely to beO_O^??V^··_O48f?10?O_i?_?8a?The defect clustersBi^"_Nb?0/0/0??10?Nb^··_Bi?0.5/0/0??10?V^··_O48f?10?O_i?_{?8 a?} were most steady under normal circumstances.