On the Bistable Behavior of a Low-Frequency Raman-Active Phonon Line in   Superconducting Oxide Ba1-xKxBiO3
  The two-loop temperature hysteresis of integrated intensity of Raman scattering of light is explained theoretically for a line of frequency 50 cm-1 in a superconducting oxide Ba1-xKxBiO3 single crystal. 
A. P. Saiko and S. A. Markevich