The influence of the bulk damping in polar crystals on the elementary
properties of surface polaritons (SP) of a mixed plasmon-phonon type i
s studied theoretically. Two different methods for the calculation of
SP damping are used. These methods are shown to give the same results.
Definite combinations of the plasmon and phonon damping constants are
found to lead to a minimum in the damping and a maximum in the planar
propagation length versus wave vector dependences. An increase in the
SP energy dissipation due to an increase in the damping constants of
elementary excitations in a crystal and the SP scattering by surface r
oughness give rise to a reduction of the SP frequency, but the shape o
f the dispersion curve changes differently, what can be distinguished
experimentally.