Structural Modulations in the High-Temperature Superconductor YBa2Cu3O7-δ and Semi Conducting WO3-x Aspects of Non-Equilibrium Behaviour

  • Ekhard K. H. Salje
Part of the NATO ASI Series book series (NSSB, volume 229)

Abstract

A thermodynamic description of non-harmonic structural modulations may be attempted in terms of the energies required to form walls (alias kinks, boundaries, areas of large structural gradients) and the inter-wall interactions. The latter are also called ‘boundary-boundary interactions’ (BBI), and they are normally repulsive in character. The wall energies can be negative, as in equilibrium incommensurate phases, or positive if the structural state is unstable or metastable. An example for narrow walls in a matrix of a perovskitetype structure are the so-called CS planes in WO3 ( Fig.l). Different wall configurations have been described in great detail for individual chemical phases (review by Sundberg, 1981a, and Sundberg, 1981b) and it was found that these walls occur in equilibrium phases with a high degree of regularity. Here we are concerned only with walls along one of the crystallographic {10n},n>2 directions. A unifying, although more simplistic view, of the various structural and chemical features is based on the observation that the essential structural building blocks of the walls are blocks of four edge-sharing octahedra which are aligned within the walls as shown in Fig.2. These structural units represent stable configurations which are accounted for within the framework of Landau-Ginzburg theory by negative Ginzburg energies:

Keywords

Tungsten Perovskite Folk 

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Copyright information

© Springer Science+Business Media New York 1990

Authors and Affiliations

  • Ekhard K. H. Salje
    • 1
  1. 1.IRC Superconductivity and Department of Earth SciencesCambridgeEngland

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