Dielectric properties perovskites

Another important group of oxide materials with a very low electrical conductivity is the oxide dielectrics. A number of these are based upon the perovskites, MXO3 or M0 X02. The archetype of these materials is BaTiC>3, which has a high dielectric constant, or relative permittivity to vacuum, the value at room temperature being 1600, and commercial use is made of the isostructural PbTi(>3 and ZrTi03 which form solid solutions, the PZT dielectrics. These materials lose their dielectric properties as the temperature... 

Perovskites AB)/3C2/303 (A = Ba, Sr, B = Zn, Mg, Co, Ni C = Nb, Ta) are promising compounds for microwave applications. It is important to synthesize these complex oxides as pure perovskite phases because the slightest admixture of a second phase hinders drastically the dielectric properties of ceramics, which sinter only at very high temperatures (1400 to 1500°Q. The precursor chemistry resembles greatly that of BaTi03 formation by alkoxide or alkoxide-hydroxide routes. Below we summarize the 3 approaches to the synthesis of these perovskites by the sol-gel method ... 

With the progress in microwave telecommunication technology, dielectric materials have come to play an important role in the miniaturization and compactness of microwave passive components. The dielectric materials available for micro-wave devices are required to have predictable properties with respect to a high dielectric constant (K), high quality factor (Qf), and small temperature coefficient of resonant frequency (TCP). Numerous microwave dielectric materials have been prepared and investigated for their microwave dielectric properties and for satisfying these requirements. In particular, complex perovskite compounds A(B,B )03... 

Several kinds of dielectric materials have been widely investigated to improve their properties and to meet the requisites of high dielectric constant (K), low dielectric loss (Qf), and low TCF. Based on these requisites, complex perovskite compound, A(B,B )03, was extensively studied from the viewpoint of the compositional and structural dependence on their microwave dielectric properties. Among them, much attention has been paid to lead-based ceramics with complex perovskite structures because of their superior dielectric properties required for microwave devices. 

As mentioned in a previous section, the dielectric properties are largely affected by the structural characteristics of solid solution. Since the bond valence is a function of bond strength and bond length," the structural characteristics largely depend on bond valence. Therefore the dielectric properties could effectively be estimated by bond valence. Let s examine the effects of A-site and B-site bond valence on the microwave dielectric properties of lead-based complex perovskite compounds. 

The ferroelectric Pb(Mgy3Nb2/3)03 (PMN) ceramic has been the snbject of extensive investigations due to its high dielectric coefficient and high electrostrictive coefficient, which renders it suitable for use in capacitors and electrostrictive actuators. However, the successful exploitation of this material is limited by the difficulty of producing a single-phase material with the perovskite structnre. Conventional solid state synthesis techniques invariably resnlt in the formation of one or more pyrochlore phases, which exhibit poor dielectric properties. 

Chapter 22 Tailoring Dielectric Properties of Perovskite Ceramics at... 

The effects of B-cation displacement upon the structures and dielectric properties of perovskite phases have been extensively studied in the important dielectric/fer-roelectric perovskite, BaTiOj. The phase shows transformations from trigonal to... 

Perovskites are vital circuit elements for many electronic purposes, from simple capacitors to dielectric resonators used in mobile phones, satellite communications, TV broadcasting and so on. The dielectric properties of bulk perovskites arise from the presence of polarisable constituents in the crystal. These include cation displacements, octahedral tilting and distortions as well as any defects present, such as grain boundaries and various point defects. The relative permittivity is the basic parameter describing a dielectric. In a static electric field this is written as (Table 6.1) but in varying electric fields is replaced by the complex relative permittivity, - is", which is a function of the frequency of the apphed electric field. 

Figure 6.3 Dielectric properties of ceramic perovskites (a) the relative permittivity and (b) the loss tangent of Stg EUgg SnO g and StgggEUgggSnOg gg as a function of temperature (c) the relative permittivity of the hexagonal 8H perovskite BagLigWJD g as a function of sintering temperature...

As a matter of fact, the tolerance factor is a rather complex crystaUo-chemical parameter, which can reflect the structural distortion, force constants of binding, rotation and tilt of the BOg octahedrons. These in turn affect the dielectric properties, transition temperature, temperature coefficient of the dielectric constant of material, and even the dielectric loss behavior in a perovskite dielectric. 

Perry CH (1971) Dielectric properties and optical phonons in para- and ferroelectric perovskite. 

Hatabayashi, K Fukumura, T and Hasegawa, T. (2012) Magnetic and dielectric properties of layered perovskite Gd2Ti207 thin film epitaxially stabilized on a perovskite single crystal. /. Appl Phys., Ill (7), 07D909-07D909-3. 

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