Crystal chemistry and dielectric properties of (Bi_1.5Zn_0.4M_0.1)(Nb_1.5Zn_0.5)O₇ (M = Sr, Ca, Mn, Zn) pyrochlore oxides

As a potentially attractive candidate of LTCC material, Bi_1.5Zn_1.0Nb_1.5O₇ ceramics with substituted Zn²⁺ were synthesized by a conventional mixed oxide route. For the first time, the effect of the chemical ionic substitution of Sr, Ca and Mn cations on the microstructure, bond energy and dielectric properties of bismuth-based pyrochlores was discussed systematically for Bi_1.5Zn_1.0Nb_1.5O₇. Rietveld refinement was carried to analyze the structure variation of the sintered specimens. The solid solubility limits of in the Bi_1.5Zn_1.0Nb_1.5O₇ system with Sr, Ca and Mn incorportion were discussed. The samples presented single cubic phase that were used to study the dielectric properties of Bi_1.5Zn_1.0Nb_1.5O₇ based on the crystallization and microstructure. The dielectric constant ε_r was mainly related to relative density not the ionic polarizability. The relative density and the dielectric constant ε_r showed the same decreased trend as a function of different ionic dopant. And the change of the grain size and grain boundaries had a significant influence on the loss tangent tanδ in this system. The A-site cation bond energy of (Bi_1.5Zn_0.4M_0.1)(Nb_1.5Zn_0.5)O₇ (M = Sr, Ca, Mn, Zn) ceramics was performed to explain the relationship between the temperature coefficient of the dielectric constant τ_ε and the crystal microstructure in a new way. With the decrease of |τ_ε| values as a function of the substitution, the Zn–O bond energy of A-site became strong. This indicated that the (Bi_1.5Zn_0.4M_0.1)(Nb_1.5Zn_0.5)O₇ system tended to be stable.