The zinc tris(thiourea) sulphate (ZTS) crystallise in the orthorhombic system, point group mm2 at room temperature [1]. The crystal is particularly interesting because of its excellent nonlinear optical properties [2]. In the range 300 – 350 K it does not show any anomalies in elastic properties [3]. In low temperatures the Raman spectroscopy data indicated anomalies at 60 and 122 K, and the phase transition was characterised as a second order one [4].

The main aim of the study was determination of the elastic properties of the ZTS crystal by Brillouin spectroscopy in the range 80 –300 K. The measurements were made on the ZTS single crystals obtained by the isothermal methods, characterised by good optical quality.

The temperature dependencies of the Brillouin shift were determined for the ZTS crystal in the principal directions and in a few mixed directions. The measurements were performed on a tandem type spectrometer made by JR Sandercock. The measuring system was described in an earlier work [5]. The results revealed anomalies in the bulk wave propagation rate and certain elastic constants at about 138 K.

[1] J. Ramajothi, S. Dhanuskodi, K. Nagarajan, Cryst. Res. Technol. 39(5) (2004) 414-420.

[2] H. O. Marcey, L. F. Warren, M. S. Webb, C. A. Ebbers, S. P. Velsko, G. C. Kennedy, G. C. Catella, Apll. Opt., 31 (1992) 5051-5055.

[3] A. V. Alex, J. Philip, J. Appl. Phys., 90(2) (2001) 720-723.

[4] M. Oussaid, P. Becker, M. Kemiche, C. Carabatos-Nedelec, phys. stat. sol.(b) 207 (1998) 103-110.

[5] B. Mroz, S. Mielcarek, J. Phys. D, 34 (2001) 395-399.

*Corresponding author, e-mail: [email protected]

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1. Elastic properties of KGd(WO₄)₂ : Ho³⁺ single crystals studied by Brillouin spectroscopy