Structures, phase transformations, and dielectric properties of (1-x)Bi₂Zn_2/3Nb_4/3O₇-xBi_1.5NiNb_1.5O₇ pyrochlore ceramics prepared by aqueous sol-gel method

Highlights: • The sol-gel process was employed to produce (1-x)β-BZN-xBNN pre-nanopowders. • The phase structure evolution procedure in (1-x)β-BZN-xBNN system was determined. • A near-zero τ_ε together with a high ε_r was obtained at 900 °C. • The structure-dielectric property relationships of the ceramics were determined. - Abstract: As a candidate of thermostable low temperature co-fired ceramics (LTCC) material, (1-x)Bi₂Zn_2/3Nb_4/3O₇-xBi_1.5NiNb_1.5O₇ (0.0 ⩽ x ⩽ 1.0) ceramics with improved dielectric properties have been prepared via aqueous sol-gel method. The relations of phase equilibrium, crystal structure and dielectric properties of the composites were investigated systematically. Phase transformation, from orthorhombic zirconolite-like to cubic pyrochlore structure, occured with the increasing Bi_1.5NiNb_1.5O₇ content. The phase stability of the orthorhombic and cubic pyrochlore phase in the (1-x)β-BZN-xBNN system was dependent on the Bi³⁺ content as well as the distribution and variety of divalent cations, such as Ni²⁺/Zn²⁺ ratio. The phase boundaries were located around x = 0.1 and x = 0.6 for orthorhombic and cubic phases, respectively. Near-zero temperature coefficient of dielectric constant (τ_ε) was obtained and the dielectric constant (ε_r) was in the range of 80-165 in this system, which were strongly correlated with phase composition. The (1-x)β-BZN-xBNN ceramic with x = 0.2 satisfied the EIA (Electronic Industries Association) specification NP0 (τ_ε≤± 30 ppm/°C between -55 and 125 °C) exhibited excellent dielectric properties of ε_r = 105.6, small dielectric tangent (tan δ) ∼ 10^-4, τ_ε = -11.1 ppm/°C with the low-firing temperature of 900 °C within the two-phase region, which can be a promising candidate for LTCC and multilayer components applications in high frequency and microwave range