Brillouin scattering and crystal optical investigations of (C 2H 5NH 3) 2CuCl 4

• Published in: Physica B + C Vol. 119; no. 3; pp. 269 - 278
• Main Authors: Kleemann, W., Schäfer, F.J., Käräjämäki, E., Laiho, R., Levola, T.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1983
• ISSN: 0378-4363
• DOI: 10.1016/0378-4363(83)90038-4

The structural phase transitions (SPT) of the layered compound (C 2H 5NH 3) 2CuCl 4 are investigated by Brillouin scattering and by crystal optical methods, which allow to propose a revised phase sequence as follows: D 17 4h (364 K) II (∼347 K) D 15 2h (∼233 K) IV (39 K) V. It contains three phases (II, IV and V) with lower than orthorhombic symmetry. The newly detected low-temperature SPT are continuous, whereas those above RT are of first order. Anomalous softening and hysteresis of C 11 and C 22 is found in the vicinity of T c2 ∼ 347 K. At T c3 ∼ 233 K these coefficients show anomalies obeying ( T c3 - T) 1 2 laws. Contributions due to 2d and 3d magnetic order are observed in the refractive indices around T N = 10.2 K.