Study On The Ions Substitution Of New Bi-based Pyrochlore Ceramics

A series of Bi based Pyrochlore Ceramics materials were prepared by conventionalsolid-state methods according to crystal chemistry principles of pyrochlore on the basis of thenew high performance quaternary pyrochlores, the effect of different site （A site or B site）substitution on structure and dielectric properties of Bi-based pyrochlore ceramics wereinvestigated. The influence of the material structure, phase composition on its dielectricproperties and dielectric relaxation mechanism were discussed, the main results are asfollows:（1） The structure and dielectric properties of (Bi_1.5MgxZn_0.5-x)(Zr_1.5Nb_0.5)O₇（BZMZN）（x=0.1、0.2、0.3、0.5） and (Bi_1.5M_0.5)(Zr_1.5Nb_0.5)O₇（M=Zn、Mg、Ca、Sr） ceramic materialshad been studied. In the (Bi_1.5M_0.5)(Zr_1.5Nb_0.5)O₇Pyrochlore Ceramics, the dielectric constantincreased first and then decreased with the ionic radius increased, which mainly related withion polarizability and ion radius.the positive temperature coefficient of dielectric constant areassociated with the impurity phase ZrO₂.In the BZMZN materials, the dielectric constantincreased with the ion polarization increase.Debye model and new glass model were used toanalysis the property of dielectric relaxation and found that the relaxation phenomenon at lowtemperature may be derived from pyrochlore materials structure in A-O’-A chain ofshort-range order, especially the Bi-O’-Bi ordered structure.（2） the effect of B site substitution on structure and dielectric properties of (Bi_1.5Zn_0.5)(M_1.5Ta_0.5)O₇（BZMT）（M=Ti、Sn、Zr、Ce） and (Bi_1.5Sr9_0.5)(Ti_1.5Nb_0.5-xSbx)O₇（BSTNS）（x=0.1、0.2、0.3、0.5） were investigated. In series BSTNS material, with Sb⁵⁺substitution quantityincrease, the material dielectric constant decreases, this may be because the smallpolarizability of Sb⁵⁺lead to the whole polarization rate becomes smaller and result todielectric constant decreases. The dielectric relaxation phenomena of Materials at hightemperature may be associated with material dynamic response of dipole. In the BZMT ceramic system, B site tetravalent substituted ions radius should not exceed0.72to obtainthe single pyrochlore structure. The low temperature dielectric loss peak On BZST, BZZT,BZCT have been used Debye model fitting, BZST and BZZT low-temperature relaxationphenomena were associated with A-O’-A ion ordered structure, BZCT relaxation phenomenonis due to dipole reorientation.（3） The dielectric properties of (Bi_1.5-xYxZn_0.5)(Ti_1.5Nb_0.5)O₇（BYZTN）（x=0.1、0.2、0.3、0.4） and (Bi_1.5-xLaxZn_0.5)(Ti_1.5Nb_0.5)O₇（BLZTN）（x=0.1、0.2、0.4、0.5） ceramic materialshad been studied. With lower amount of Y2O3substituted （x＜0.4）,the crystal structure wasstill cubic pyrochore.when La³⁺substitutied x>0.1, the crystal structure gradually transformsfrom pure pyrochlore to LaNbO₄phase and pyrochlore. With Y3+replace quantity increase,the dielectric constant decreases, this is mainly because the Y ion polarizability is smaller andmakes dielectric constant decreases. The dielectric loss peak in the BLZTN may be due to adefect dipole...