2D and 3D Ordering Transitions in the Weak CDW Material Deuterated PtI.
Abstract
We model the recently observed (J.-F. Bardeau et al., Acta Cryst. B52), 854 (1996). two- and three-dimensional structural ordering transitions in the commensurate weak charge-density-wave (CDW) halogen-bridged transition metal linear chain (MX) materials PtI and deuterated PtI. The order-disorder transitions are interpreted in terms of a competition between Coulomb (Madelung) and van der Waals (caused by charge fluctuations) energies. The Madelung energy is evaluated using the first order perturbation theory. The contribution from the van der Waals interaction is calculated within the second order perturbation theory using the small cluster and small dipole approximations. The temperature dependence of the lattice distortion shows a crossover from an ``in-phase" to an ``out-of-phase" ordering between adjacent CDW chains as the temperature is lowered. We show that it is energetically favorable for the sheets (of atoms) to slide with respect to each other at low temperatures after an ordering of disordered sheets.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 1997
- Bibcode:
- 1997APS..MAR.S1403B