Crystal structures, phase stability, and dielectric properties of (1−x) Bi_3/2MgNb_3/2O₇−x Bi₂Zn_2/3Nb_4/3O₇ ceramics

Highlights: • The sol–gel process was employed to produce BMN and β_BZN pre-nanopowders. • Phase evolution procedure in (1−x) BMN–x β_BZN ceramics was determined. • Tolerance factor was employed to providing an indication of structural stability. • Dielectric properties were related to phase structure, composition and stability. - Abstract: The preparation, crystal structures, phase stability and dielectric properties of the (1−x) Bi_3/2MgNb_3/2O₇−x Bi₂Zn_2/3Nb_4/3O₇ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) ceramics were investigated systematically. The sol–gel process was employed to produce crystalline, single-phase Bi_1.5Mg_1.0Nb_1.5O₇ (BMN) and Bi₂(Zn_2/3Nb_4/3)O₇ (β_BZN) pre-nanopowders for the synthesis of the ceramics. X-ray diffraction data indicated that these ceramics presented a phase transition for Bi³⁺ and Zn²⁺-rich specimens (x ⩾ 0.6), from cubic pyrochlore to orthorhombic zirconolite-like structure. The tolerance factor (t) combined with r_A/r_B value and the lattice energy (U) were employed to provide an indication of the structural stability of the (1−x) BMN–x β_BZN cubic pyrochlores (x ⩽ 0.4). The tolerance factor (t) calculation contain more structural information, which gives further insight into the details of the structural stability features in the (1−x) BMN–x β_BZN cubic pyrochlores. The relationships between the crystal structures and dielectric properties of the ceramics were determined, and the dielectric loss was related to the phase stability of the system. It is suggested that the dielectric properties are mainly determined by the phase structure, composition and stability in the (1−x) BMN–x β_BZN system