The variety of vibration frequency with tetragonal strain shows that the soft mode frequency increases with the tetragonal strain increasing followed by the transition of unstable soft mode to stable vibrational mode at a certain critical point.

• 振动频率随四方应变的变化关系表明，随著四方应变的增大，软模的频率增大，在某一个临界点，不稳定的软模转变为稳定的振模。