Time-resolved structure analysis of piezoelectric crystals by X-ray diffraction under alternating electric field

Rare-earth substitution effects on atomic motions in resonantly vibrating piezoelectric oscillators of langasite-type crystals, namely, La3Ga5SiO14 (LGS) and Nd3Ga5SiO14 (NGS), are revealed by time-resolved X-ray crystal structure analysis under alternating electric fields. Deformations of Ga-O-Ga and Ga-O-Ga/Si bond angles accompanying deformations of RE-O (RE: La or Nd) bond lengths found in LGS are suppressed in NGS. Alternatively, rigid GaO6 octahedra are deformed in NGS. The decreases in RE-O bond lengths and Ga-O-Ga and Ga-O-Ga/Si bond angles caused by the substitution of La by Nd would make the bond lengths and angles more difficult to deform under electric fields; hence, the piezoelectric constants of NGS are smaller than those of LGS.