Effect of Ordering‐Induced Domain Boundaries on Low‐Loss Ba(Zn_1/3Ta_2/3)O₃‐BaZrO₃ Perovskite Microwave Dielectrics

Abstract

Small substitutions of BaZrO, into Ba[(Zn,Ni),Ta,]O, are utilized in the commercial preparation of low-loss perovskite microwave dielectrics. The structures of a series of these phases with substitution levels ranging from 1% to 5% BaZrO, were examined using high-resolution TEM.For I2.15% BaZrO, the solid solutions retain the ordered "1:2" structure of the Ba[(Zn,Ni),,Ta,]O, end-member but are comprised of small ordered domains whose size decreases as the Zr content is raised. The decrease in the size of the domains parallels a decrease in the processing time required to access a low-loss state. Although for pure Ba[(Zn,Ni),,Ta,]O, reductions in the degree of cation order produce a large increase in the dielectric loss, the Zrsubstituted ceramics retain a very low loss. We believe the low losses of the 1:2 ceramics are derived from the stabilization of the ordering-induced domain boundaries via the partial segregation of the Zr cations. For substitutions between 3% and 5 % BaZrO, the size of the ordered domains continues to decrease but the system undergoes an abrupt transformation to a cubic "1:l" ordered structure with a doubled perovskite repeat. The structures of these phases have been interpreted using a "random layer" model in which one site is occupied by Ta and the other by a random distribution of Zn, Zr, and the remaining Ta cations, i.e., ing is confined to nano-sized domains, these ceramics also exhibit low losses, again reflecting the relative stability of the domain boundaries. In this case we believe the low losses reflect the effectiveness of the random layer in stabilizing the anti-phase boundaries.

Low-Loss Microwave Dielectrics for Different Frequency Ranges

“…[15]. Davies et al [15] have found that the formation of 1:2 ordered structure in these materials starts in small-size domains distributed in the disordered matrix [15]. They have shown the important role of Zr 4+ in the stabilization of domain walls that facilitates ordering processes in a material, and hence improves its Q-factor magnitude.…”

“…Therefore, by varying both -the ratio between the A-site ions (change in x) and the concentration of substituting ion in the BLTss, we can obtain the materials with high permittivity and quality-factor, and near-zero controllable temperature coefficient τ f (Table I). [15]. Davies et al [15] have found that the formation of 1:2 ordered structure in these materials starts in small-size domains distributed in the disordered matrix [15].…”

Fabrication, Characterization, and Modulation of Functional Nanolayers

“…Using the lattice parameters obtained from XRD [δ = ðq x sub − q x film Þ ̸ q x film = + 0.0435], the estimated dislocation spacing is 8.7 nm, suggesting that the dislocations fully relax the strain in the film. Although superspots originating from the (111) diffraction are often observed in AB 0.5 B' 0.5 O 3 compositions that crystallize in B-site-ordered double perovskite structures [26], they are not observed in the SrTi 0.5 Nb 0.5 O 3 film (Fig. 10.4b).…”

Nueva Generación de Materiales LTC

“…When developing high-Q materials, properties such as crystal-structure dynamics, tolerance factors, electronic and atomic structure, etc have to be considered. These fundamental properties translate into several structural criteria that must be met in order to produce the high-Q material: the structure must be packed as close as possible [1,2]; different ions residing at the particular crystallographic site should differ in size as little as possible [3]; the cation ordering should be induced to reduce the anharmonicity of the crystal-lattice dynamics and eliminate the effects of the disordered charge distribution and further constrain the structure [4,5]; the reduction (or oxidation) of the ceramics must be avoided to suppress the conductivity [6]; the concentration of structural defects must be minimized and not associated with the strain fields [4]; the ceramics must be free of deleterious secondary phases [7]; and the grain boundaries must be clean of precipitates and liquid phase [8].…”