EFFECT OF THERMAL CYCLING ON NORMAL-STATE THERMAL-PROPERTIES OF YBA2CU3O7-X FILMS

The photopyroelectric (PPE) technique has been used to study the effec t of thermal cycling on normal state thermal properties of YBa2Cu3O7-x thin films. For an optically opaque and thermally thin 'sample, the P PE voltage amplitude (V) is inversely proportional to the specific hea t of the sample. Hysteresis in V as a function of temperature is obser ved and annealing of films at T=325 K enhances the magnitude of hyster esis. For annealed films, the magnitude of hysteresis reduces slowly a s a function of time and in some films it disappears after a period of more than 24 h at 295 K. Two peaks in V-1 at T=110 to 140 K and at T= 200 to 240 K have been observed. The peak at T=200 to 240 K has been o bserved only during the heating path for samples cooled to a temperatu re less than 150 K. No hysteresis in the resistance as a function of t emperature is observed, but annealing at 325 K reduces the magnitude o f the resistance.