The dielectric response of ferroelectric-dielectric composites is theoretically addressed. Dielectric permittivity, tunability (relative change of the permittivity driven by dc electric field), and loss tangent are evaluated for various composite models. The analytical results for small dielectric concentration and relative tunability are obtained in terms of the traditional electrostatic consideration. The results for large tunability are obtained numerically. A method is proposed for the evaluation of the tunability and loss at large concentrations of the dielectric. The basic idea of the method is to reformulate the effective medium approach in terms of electrical energies stored and dissipated in the composite. The important practical conclusion of the paper is that, for random ferroelectric-dielectric composite, the addition of small amounts of a linear dielectric into the tunable ferroelectric results in an increase of the tunability of the mixture. The loss tangent of such composites is shown to be virtually unaffected by the addition of moderate amounts of the low-loss dielectric. The experimental data for (Ba,Sr)TiO3 based composites are analyzed in terms of the theory developed and shown to be in a reasonable agreement with the theoretical results.

The ceramic Ba8ZnTa6O24 has been synthesized in isolation and its dielectric and crystallographic properties characterized. The material affords excellent dielectric properties, with a high unloaded quality factor Qu=20 800 at 3.28 GHz, high relative permittivity εr=29 and a temperature coefficient of resonant frequency τf=29.4 ppm/°C. The crystal structure adopted is complex, comprising mixed cubic and hexagonal perovskite subunits, and contains cation vacancies on the octahedral sites. A second phase with a closely related structure is identified, demonstrating the existence of a family of materials. This structural complexity offers diverse opportunities for substitutions calculated to enhance the figures of merit reported.

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The search for multiproperty materials, [1] in which one cooperative phenomenon can control another through modulation of the local structure and bonding, is complicated by the need to separate the chemical units responsible for these different properties. Thus, rules are required for the synthesis of materials that assemble with spatial segregation of the elements conferring distinct properties. These rules should be sufficiently strict to operate at the high synthesis temperatures required for processing many inorganic materials.This challenging synthetic task can be addressed by exploiting the diversity of site chemistries [2] available in a complex perovskite structure and harnessing the combination of the specific bonding requirements of the d 0 cations and the site symmetries in the structure to drive the cation ordering. cations in the structure. These site-ordered solids are then processed to permit their evaluation as microwave dielectric resonators.In the chemistry of transition-metal oxides, elements in the d 0 oxidation state (particularly Ta V , Ti IV , and Nb V ), with their characteristic directional MÀO multiple bonding, are the basic components of ferroelectric, relaxor, and high-permittivity materials.[3] Transition-metal centers that bear d electrons (d n centers) confer magnetic, optical, and electronic properties on materials. The development of extended metal oxide networks in which d n centers can be separated by long distances with precise site order within a d 0 matrix offers great potential in materials design. The ordering of cations of different sizes and charges is possible on the octahedral B site of the ABO 3 perovskite structure [4]