The sequence of phase transitions and the symmetry of in particular the low temperature incommensurate and spin-Peierls phases of the quasi one-dimensional inorganic spin-Peierls system TiOX (TiOBr and TiOCl) have been studied using inelastic light scattering experiments. The anomalous first-order character of the transition to the spin-Peierls phase is found to be a consequence of the different symmetries of the incommensurate and spin-Peierls (P21/m) phases. The pressure dependence of the lowest transition temperature strongly suggests that magnetic interchain interactions play an important role in the formation of the spin-Peierls and the incommensurate phases. Finally, a comparison of Raman data on VOCl to the TiOX spectra shows that the high energy scattering observed previously has a phononic origin.
@article{arxiv.0704.0170,
title = {Symmetry disquisition on the TiOX phase diagram},
author = {Daniele Fausti and Tom T. A. Lummen and Cosmina Angelescu and Roberto Macovez and Javier Luzon and Ria Broer and Petra Rudolf and Paul H. M. van Loosdrecht and Natalia Tristan and Bernd Buchner and Sander van Smaalen and Angela Moller and Gerd Meyer and Timo Taetz},
journal= {arXiv preprint arXiv:0704.0170},
year = {2009}
}