Long-wavelength optical phonons ofGa1−xAlxNsolid solutions have been identified in a wide compositional range by Raman spectroscopy. TheA1andE1polar phonon frequencies evolve continuously withxfrom one-member crystal to the other. The same behavior seems to hold true for the silentB1mode, which manifests itself by an interference with an unidentified continuum. Coupling of the longitudinal-optic (LO) modes associated with the two types of bonds, via the macroscopic electric field, is treated by a generalization of the dielectric model [D. T. Hon and W. L. Faust, J. Appl. Phys.1, 241 (1973)]. This approach accounts for the observed frequencies and supports the apparent one-mode behavior of the polar LO phonons. ©1998 American Institute of Physics.