Eur. Phys. J. B 35, 339-348 (2003)
https://doi.org/10.1140/epjb/e2003-00286-0

NQR study of phase transitions in CH₃HgX (X=Cl, Br, I)^*

¹ Institute of Mathematics, Physics and Mechanics, Univ. of Ljubljana, POB 2964, 1000 Ljubljana, Slovenia
² Fac. of Mathematics and Physics, Univ. of Ljubljana, POB 2964, 1000 Ljubljana, Slovenia
³ R. Bošković Institute, POB 1016, 10001 Zagreb, Croatia

Corresponding author: ^a janez.pirnat@imfm.uni-lj.si

Received: 16 January 2003
Revised: 23 June 2003
Published online: 15 October 2003

Abstract

The temperature dependence of halogen nuclear quadrupole resonance (NQR) in the series CH₃HgX (X=Cl, Br, I) is measured with special emphasis on the structural phase transitions at 310 K, and ~400 K, respectively. In the temperature dependences of NQR frequencies similarities are observed and discussed in relation with the structure and thermal vibrations on both sides of the phase transition. On the basis of known data a mechanism for the three analogous phase transitions is proposed. The chlorine spin-lattice relaxation behaviour in CH₃HgCl can be explained by a competition of fast thermal fluctuations of MMX molecules across the high temperature (h.t.) mirror plane and of infrequent transitions to the other equivalent fluctuation mode across the orthogonal h.t. mirror plane. Proton high temperature relaxation is probably dominated by the same slow motion, but at lower temperatures some other mechanism involving magnetic coupling prevails.