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

用x射线单晶衍射仪分析了用于宽带SAW滤波器的压电Langasite （La_3Ga_5SiO_<14>）单晶的结构。本物理年，在日本东北大学进行了高压和强电场下的实验，阐明了langasite晶体的压电机理。采用Czochralski法生长La_3Ga_5SiO_<14> (LGS)和Nd_3Ga_5SiO_<14> (NGS)。采用四轴单晶衍射仪对高压（3.3和7.4 GPa）下放置在金刚石砧池中的langasite晶体结构进行了分析。用红宝石荧光技术测量压力。阐明了高压下a方向的线压缩性大于c方向的线压缩性。上一物理年常压下实验预测的变形各向异性，在高压实验中得到了证实。为了证实langasite结构在a_1-a_2平面上的压缩性，根据所得的晶体结构数据计算了带阳离子多面体的体积和变形。在高压下，在La和Ga多面体上发现了特定的离子变形。基于La和Ga多面体位点的体积变化和变形，证实了langasite上的压电机制是由于阳离子沿[100]的位移（即电荷平衡的破坏）。沿着这个方向[100]，实际观察到了压电性。为了确认电磁场作用下的逆压电性（电致伸缩），进行了晶体结构分析，但由于小球形晶体表面的放电，没有观察到晶体结构的差异。综上所述，基于高压下晶体结构的变形，沿[100]阐明了电平衡铁电langasite的压电机理。少

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