PHASE-TRANSITION BEHAVIOR IN THE PEROVSKITE-TYPE LAYER COMPOUND (N-C12H25NH3)2CUCL4

The solid state phase transitions in the perovskite-type layer compoun d (n-C12H25NH3)2 CuCl4 have been studied by X-ray diffraction, differe ntial scanning calorimetry and i.r. spectroscopy. Two-step reversible phase transitions are observed at T(c1) = 327.9 K and T(c2) = 335.7 K on heating whereas at T(c1) = 324.4 K and T(c2) = 330.1 K on cooling, accompanied with the increase of interlayer distance (DELTAd1 congruen t-to 1.8 angstrom and DELTAd2 congruent-to 0.85 angstrom, respectively ). In the first transition important melting of the hydrocarbon chains occurs together with the flipping of polar NH3 groups. Defects of the gt3g' and end gauche forms are found. The weakening of the NH-Cl hydr ogen bonds is also observed. Further conformational changes of the hyd rocarbon part are dominantly observed in the second phase transition. As the interlayer spacing is increased, only short gtg' kinks are allo wed. The mechanism of conformational transition for this compound can be therefore suggested as follows: gt9 or tgt8 --> 2g - 2 kink (-gt3g' -) --> 2g - 1 kink (-gtg'-).