Abstract: In this paper,the curves of slowness in (100),(010) and (001) for GaPO4 have been plotted.The maximum of acoustic velocities and their directions have also been gained,and compared with that of α-SiO2.Crystal orientation dependence of piezoelectric constant d11 and electromechanical coupling factor k11 have been calculated phenomenologically.The maximum of longitudinal piezoelectric constant d11 and electromechanical coupling factor k11 are obtained.The orientation was also determined.It is found that the d11 and k11 of GaPO4 are much larger than that of SiO2 and the velocity of acoustic wave is smaller than that of SiO2.These results will give certain directions for the use of GaPO4 in piezoelectrical and acoustic-optical devices.

Key words: In this paper,the curves of slowness in (100),(010) and (001) for GaPO4 have been plotted.The maximum of acoustic velocities and their directions have also been gained,and compared with that of α-SiO2.Crystal orientation dependence of piezoelectric constant d11 and electromechanical coupling factor k11 have been calculated phenomenologically.The maximum of longitudinal piezoelectric constant d11 and electromechanical coupling factor k11 are obtained.The orientation was also determined.It is found that the d11 and k11 of GaPO4 are much larger than that of SiO2 and the velocity of acoustic wave is smaller than that of SiO2.These results will give certain directions for the use of GaPO4 in piezoelectrical and acoustic-optical devices.