Pseudospin Clusters and Short-Range Correlations
Structural phase transformations constitute a major subject of investigation in thermodynamics of crystalline states. A partial displacement in the constituent molecule represented by an order variable is essential for describing structural changes. Although considered as primarily independent of the lattice structure, such an order variable in finite magnitude disrupts local symmetry in a crystal. Correlations of these variables between adjacent sites are responsible for their clustering, leading to a macroscopic symmetry change. Following Born and Huang, we consider clustered order variables in a short range to form condensates for minimal structural strains in the lattice. Consequently, a condensate is characterized by a specific wave vector for propagation in the lattice. In this chapter, we define pseudospins for binary order variables and discuss the nature of their correlations in short range.
KeywordsOrder Variable Correlation Energy Classical Vector Structural Phase Transformation Constituent Molecule
- 2.M. Born and K. Huang, Dynamical Theory of Crystal Lattices (Oxford University Press, Oxford, 1968)Google Scholar
- 7.R. Blinc and B. Zeks, Soft Modes in Ferroelectrics and Antiferroelectrics (North-Holland, Amsterdam, 1974)Google Scholar
- 8.T. Nagamiya, Solid State Physics, Vol. 20 (Academic, New York, 1963); L. R. Walker, Magnetism I (Academic, New York, 1963)Google Scholar
- 10.C. Kittel, Quantum Theory of Solids (Wiley, New York, 1963)Google Scholar
- 11.M. J. Rice, Charge Density Wave Systems in Solitons and Condensed Matter Physics, ed. A. R. Bishop and T. Schneider (Springer, Berlin, 1978)Google Scholar