mass in the primitive cell on the dispersion relationship of one-dimensional three- atom chain.

The basic law of the spectral width and the frequency band gap changing with the atomic mass are established. The results show

that when the mass of only one atom in the primitive cell changes，the width of the acoustic wave spectrum decreases with the increase

of any atomic mass. The spectral width of optical waves increases with the increase of the mass of small atoms，and decreases with the increase of the mass of large atoms. Both frequency band gaps are narrowed with increasing the mass of the small atom，and widened with increasing the mass of the large atom. As the mass of the intermediate atoms increases，the frequency forbidden band between low-frequency optical waves and acoustic waves gradually is narrowed，while the frequency forbidden band between high-and low-frequency optical waves is gradually widened. The rel-evant results provide a theoretical basis for the design of crystal band-pass filters.