Relative permittivity dielectric 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 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...

Chapterb- The perovskite family of materials is of considerable technological importance for its excellent temperature stable microwave properties for dielectric resonator based filters, oscillators and antenna applications. In this chapter author review the preparation, characterization and the microwave dielectric properties of Ca[(Lii/3A2/3)i-xMx]03.5 [A=Nb, Ta and M=Ti, Zr, Sn] dielectric ceramics. This family of perovskite materials shows relative permittivity in the range 20 to 56 with a quality factor up to 45000 GHz and temperature coefficient of resonant frequency (xf) in the range from -21 to +83 ppm/°C. The Xf can be tailored by adjusting the titanium content. The sintering temperature can be lowered below 950 °C to suit LTCC by the addition of low melting glasses. 

Technically useful properties of such perovskite ceramics are their high permittivities (relative dielectric constants), the semiconductor properties of certain chemical compositions and their piezoelectric properties. 

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