Experimental assessment of nonergodicity in tetracene single crystals

Dielectric spectroscopy is applied to the study of phase transitions in the range from room temperature down to 12 K in single crystals of tetracene (TEN), a well-known material which, like most organic semiconductors, shows polymorphism. The present analysis, through proper experimental procedures, permits us to identify the wide range (T > 150 K) of instabilities and of strong hysteresis effects as clear evidence of a nonergodic state and then also to clarify some open questions, first of all the role of the sample thermal history, including the temperature variation rate and some apparent sample dependence of the results. Furthermore evidence is obtained of two transitions at 144 and 45 K.