Material Design of New Piezoelectric Crystal Langasite based on the Crystal Structure

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Structures of the piezoelectricity Langasite (La_3Ga_5SiO_<14>) single crystals for wide band SAW filter were analyzed by X-ray single crystal diffractmeter. In this physical year, experiments under the high pressure and the high electric field have been performed at Tohoku University Mechanism of piezoelectricity on the langasite crystal has been clarified.The La_3Ga_5SiO_<14> (LGS) and Nd_3Ga_5SiO_<14> (NGS) were grown by Czochralski method. The crystal structure of langasite putting in diamond anvil cell (DAC) with high pressure (3.3 and 7.4 GPa) was analyzed by 4-axis single crystal diffract meter. The pressure was measured by the ruby fluorescence technique.It was clarified that the linear compressibility of a-direction is greater than that of c-direction under the high pressure. This anisotropy of deformation anticipated by the experiments under the normal pressure performed in the last physical year was confirmed by high pressure experimental. For the confirmation of the compres … More sibility on the a_1-a_2 plane of langasite structure, volumes and deformation of polyhedra with cations are calculated based on the crystal structure data obtained. Specific ionic deformation on the La and Ga polyhedral sites under the high pressure has been found. It was confirmed that mechanism of piezoelectricity on the langasite is due to cation displacement (that is the destruction of charge balance) along [100] based on the volume change and deformation of the La and Ga polyhedral sites. Along this [100] direction, piezoelectricity has been observed practically For the confirmation of the inverse piezoelectricity (electrostriction) under the electric-magnetic field, crystal structure analysis was performed but the crystal structural difference was not observed because of discharge on the surface of small spherical crystal.In summary, mechanism of piezoelectricity of ferroelectric langasite with electric balance was clarified along [100] based on crystal structural deformation under the high pressure. Less