Structures, phase transformations, and dielectric properties of (1−x)Bi2Zn2/3Nb4/3O7–xBi1.5NiNb1.5O7 pyrochlore ceramics prepared by aqueous sol–gel method

Abstract

As a candidate of thermostable low temperature co-fired ceramics (LTCC) material, (1−x)Bi2Zn2/3Nb4/3O7–xBi1.5NiNb1.5O7 (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 Bi1.5NiNb1.5O7 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 (τε) was obtained and the dielectric constant (εr) 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 (τε≤± 30ppm/°C between −55 and 125°C) exhibited excellent dielectric properties of εr=105.6, small dielectric tangent (tanδ)∼10−4, τε=−11.1ppm/°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.