Exciton–phonon interaction and Raman spectra of [(CH 3 ) 2 NH 2 ] 5 Cd 2 CuCl 11 crystals

• Published in: physica status solidi (b) 2004-09, Vol.241 (11), p.2620-2628
• Main Authors: Kapustianik, V., Batiuk, A., Czapla, Z., Podsiadła, D., Czupiński, O., Eliyachevskyy, Yu, Rudyk, V.
• Format: Article
• Language: English
• ISSN: 0370-1972; 1521-3951
• DOI: 10.1002/pssb.200302057

Temperature evolution of the exciton–phonon interaction (EPI) in ((CH 3 ) 2 NH 2 ) 5 Cd 2 CuCl 11 solid solution was studied on the basis of absorption spectroscopy data. The obtained values of effective phonon energies were compared with the data of Raman spectroscopy. It is shown that the ( T ) and E ′ parameters of Urbach's rule show the continuous anomalous change characteristic of the second‐order phase transition at T 1 = 176 K. The anomalous behaviour of the EPI and other spectral parameters at T 0 = 310–315 K was related to the complex co‐operative effect involving weakening of the hydrogen bonds and variation of the Jahn–Teller distortion of metal–halogen polyhedra with temperature. This process takes place only within the copper–chlorine sublattice and due to this would be hardly related to the usual phase transition. At the same time, the considered temperature change of the tetragonal distortion of the metal–halogen octahedra is followed by nonfulfillment of Urbach's rule in the temperature range T T 0 . (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)