ANOMALOUS BEHAVIOR OF THE URBACH EDGE AND PHASE-TRANSITIONS IN TLGASE2

The long-wavelength tail of the optical absorption TiGaSe//2 crystals at alpha equals 30-150cm** minus **1 is shown to obey Urbach's absorption in in the temperature range 4. 2-294 degree K. The anomalous behaviour of the parameters of this rule suggests the presence of two phase transitions in TlGaSe//2 at 246 degree K and 101 degree K beside the known phase transitions at 120 degree K and 107 degree K. The presence of phase transitions in TlGaSe//2 at 246 degree K and 101 degree K is also confirmed by means of heat capacity measurement.