Dielectric rare earth aluminates

Dielectric data for microwave dielectric materials, namely, the relative dielectric permittivity (e,), the product of the quality factor Q and the frequency (Q x/), the frequency of the measurement (/), and the temperature coefficient of the resonance frequency (xf) based on rare earth aluminates are listed in Table 30. Measurements carried out using low-frequency (MHz) impedance methods are... 

Practical interest in rare earth aluminates as microwave dielectric materials remains high. Recently, Shevlin et al. (2005) reported that La cYi- AlOs solid solutions (0.2 possible application as gate dielectrics (which would offer an alternative to silicon dioxide in complementary metal-oxide semiconductor devices) when stabilized in the rhombohe-dral perovskite structure. The needed properties are lost in the orthorhombic modification. Flowever, our previous consideration of the crystal structure (see Section 2.3.1) together with the results of Kyomen and Itoh (2002) reveal that this feature is difficult to realize in practice, that is the rhombohedral modification of Laj Yi j A103 solid solution only exists in a narrow concentration range with X > 0.85, while in the range 0.2 < x < 0.4, the crystal structure will remain orthorhombic. 

The fact that dielectric and structural properties of rare earth aluminates fulfil the demands of microwave engineering, even though some other properties (primarily the formation of twins and chemical purity of precursors) are unfavourable, should continue to support a considerable interest in the attempts to tailor new varieties of aluminate crystals. 

In contrast to rare earth aluminates, the microwave dielectric properties (dielectric permittivities and losses) of rare earth orthogallates were studied less. The relative dielectric permittivity in LaGaOa has been reported to be 25 (Sandstrom et al., 1988), in PrGaOa, is 24 (Sasaura et al., 1990a), whereas in neodymium gallate, from 20 to 23 were given by different authors (Konaka et al., 1991 Konopka and... 

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