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声表面波滤光片的朗加石(La3Ga5SiO；14)单晶的结构。在本物理年，东北大学进行了高压高压电场下的实验，阐明了La3Ga5SiO；14&gt；(LGS)和Nd3Ga5SiO；14&gt；(NGS)晶体的压电性机理。用四轴单晶衍射仪分析了在高压(3.3和7.4 GPaDAC)中放置的硅锌矿的晶体结构。用红宝石荧光法测量了压力，发现高压下a方向的线性压缩系数大于c方向的线性压缩系数。上一物理年常压实验所预测的变形各向异性得到了高压实验的证实。确认压缩…根据得到的晶体结构数据，计算了含阳离子的多面体在a_1-a_2面上的可能性、体积和形变。发现La和Ga多面体晶位在高压下发生了特殊的离子形变。根据La和Ga多面体晶位的体积变化和形变，证实了Langasite的压电性机制是由于[100]方向的阳离子位移(即电荷平衡的破坏)所致。沿着这个[100]方向，实际观察到了压电性，证实了在电磁场作用下的逆压电性(电致伸缩)，并进行了晶体结构分析，但由于小球晶表面的放电，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，阐明了具有电平衡的铁电花岗岩沿[100]方向的压电性机理。较少

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