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

As a candidate of thermostable low temperature co-fired ceramics (LTCC) material, (1-x)Bi2Zn2/3Nb4/3O7-xBi(1.5)NiNb(1.5)O(7) (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)beta-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 (tau(epsilon)) was obtained and the dielectric constant (epsilon(r)) was in the range of 80-165 in this system, which were strongly correlated with phase composition. The (1-x)beta-BZN-xBNN ceramic with x = 0.2 satisfied the EIA (Electronic Industries Association) specification NP0 (tau(epsilon) <= + 30 ppm/degrees C between -55 and 125 degrees C) exhibited excellent dielectric properties of epsilon(r) = 105.6, small dielectric tangent (tan delta) similar to 10(-4), tau(epsilon) = -11.1 ppm/degrees C with the low-firing temperature of 900 degrees C within the two-phase region, which can be a promising candidate for LTCC and multilayer components applications in high frequency and microwave range. (C) 2014 Elsevier B.V. All rights reserved.