Phonon Relaxation Due to Anharmonism and Central Peak in Structural Phase Transitions I. Soft Optic Modes and Acoustic Phonons in Cubic Crystals

In the mode–mode coupling approximation the critical exponente (CE) are calculated for the damping and frequency shift of soft optic modes and acoustic phonons at the structural transition point for crystals with dimensions d = 1, 2, 3. The CE are traced back to the anharmonic interaction of phonons taking into account the intrinsic dynamic central peak of any nature. Anharmonisms of all order are considered. [Russian Text Ignored].