New AィイD23ィエD2BCィイD23ィエD2DィイD22ィエD2OィイD214ィエD2-type single crystal materials for piezoelectric applications

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Recent progress in electronic technology requires new piezoelectric crystals having superior properties such as zero temperature coefficients and large electromechanical coupling factors. We have developed a series of new leading candidates to satisfy those requirements : LaィイD23ィエD2GaィイD25ィエD2SiOィイD214ィエD2 (Langasite, LGS), LaィイD23ィエD2NbィイD20.5ィエD2GaィイD25.5ィエD2OィイD214ィエD2 (LNG) and LaィイD23ィエD2TaィイD20.5ィエD2GaィイD25.5ィエD2OィイD214ィエD2 (LTG). Since LGS-type structure has 4 kinds of sites (AィイD23ィエD2BCィイD23ィエD2DィイD22ィエD2OィイD214ィエD2), it has high potential for creation of new materials with better properties. By isovalent substitution, a series of LGS-type crystals have been synthesized. The determination of lattice constants for these crystals showed that an increase of lattice constants is advantage for the increment of piezoelectric moduli. Especially, and increase of an average ionic radius in A-site was found to be effective. According to this tendency, new materials have been synthesize … More d by two kinds of aliovalent substitutions, one is the substitution with A-site, and the other is that with all A-, B-, C-, D-sites. Crystallinity of these materials was examined by the micro pulling-down technique. Among them, transparent LaィイD23-xィエD2SrィイD2xィエD2TaィイD20.5+x/2ィエD2GaィイD25.5-x/2ィエD2OィイD214ィエD2 and SrィイD23ィエD2TaGaィイD23ィエD2SiィイD22ィエD2OィイD214ィエD2 micro single crystals without crack formation were grown. Subsequently, single crystals of these materials 1 inch in diameter have also been grown by the Czochralski technique, at a pulling rate of 0.6 mm/h. Obvious variation of lattice constants and chemical composition of these crystals along the growth axis was not observed. They showed superior piezoelectric properties comparable to LGS, LNG and LTG.Using LGS single crystals, we made monolithic-type filters (10.4 and 21.4 MHz) with low input and output impedance, small size and with low attenuation, compared with those made of quartz. A 71MHz wide passband SMD filter for the GSM base station was also made and exhibited superior properties. The volume of a 71 MHz LGS filter is 1/5 that of a conventional discrete-type one made of quartz. Less