Loss spectra of pure and La-doped MgTiO 3 microwave ceramics
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J. Petzelt, G. A. Komandin,a) and V. V. Voitsekhovskiia) Institute of Physics, Czech Academy of Sciences, Na Slovance 2, 18040 Prague 8, Czech Republic (Received 19 September 1994; accepted 2 December 1994)
Pure and La-doped magnesium titanate (MgTiO 3 ) microwave ceramics were sintered and structurally and dielectrically characterized. Doping provides small inclusions of a second phase found to correspond to the La 2 Ti 2 0 7 compound. It increases the microwave dielectric loss appreciably and gives rise to three absorption peaks in the submillimeter range assigned to polar phonons of the La 2 Ti 2 0 7 structure. This assignment was confirmed by a direct reflectivity measurement on La 2 Ti 2 O 7 ceramics. From the temperature dependence of submillimeter losses in the pure sample, one can estimate that from 1000 down to at least 8 GHz about half of the room temperature losses are intrinsic, i.e., due to two-phonon absorption processes.
I. INTRODUCTION The development of microwave communication systems initiated by a broader and faster need of information gave birth to research on new materials for such applications, namely, as resonators for microwave circuits.1-2 In order to satisfy this particular demand, these materials should present a suitable permittivity value (e r > 10), a low dielectric loss (tan S < 5 X 10~4) in a microwave frequency range, and also a stable value of their working frequency concerning variations on room temperature (jf ~ 0). There is a group of dielectric ceramic materials that fulfill these requirements and have been investigated for microwave resonators.2"4 Among these ceramic materials are the ones with compositions based on magnesium titanate (MgTiO 3 ). 5 " 7 An interesting area of research is the establishment of relationships between processing, final microstructures, and microwave dielectric properties. The importance of processing on dielectric properties was addressed in an earlier paper.7 Of particular interest is the study of microwave dielectric loss mechanisms in this material. A comprehensive study on this matter was undertaken based on far infrared spectroscopy.8 This technique has been used to help the characterization of microwave dielectric properties of some lowloss materials.9"11 Microwave permittivity and dielectric loss were extrapolated from infrared data and correlated with polar lattice vibration modes. Extrapolation from far infrared region down to microwave frequencies has been done quite successfully for several materials.8-9'12 a)
On leave from the Institute of General Physics, Russian Academy of Sciences, Vavilov Street 38, 177333 Moscow, Russia. J. Mater. Res., Vol. 10, No. 9, Sep 1995 http://journals.cambridge.org
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In our previous work,8 several MgTiO3-based compositions were studied in order to elucidate the effect of different factors on dielectric loss, namely, to separate the intrinsic from the extrinsic nature of those factors that contribute to dielectric loss. Among the studied compositions, La-doped MgTiO3 has revealed a
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