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Landau theory
About: Landau theory is a research topic. Over the lifetime, 2882 publications have been published within this topic receiving 57078 citations.
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TL;DR: In this paper, a Landau-Ginzburg functional of two order parameters (charge-density φ and mass-density deviation η) is developed in order to yield a field theory relevant to ionic lattice gases as well as a family of off-lattice models of ionic fluids that go beyond the restricted primitive model (RPM).
36 citations
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01 Jan 1992TL;DR: In this article, the stability field of cordierite with respect to enstatite + sillimanite + quartz is reduced due to the orientational disordering of CO3 groups in calcite.
Abstract: When calculating the stability fields of different mineral assemblages, petrologists have become used to dealing with two broad categories of reactions. In the first category are heterogeneous reactions between unrelated phases, such as jadeite ⇋ albite + quartz, or between phases with the same composition but different structure, such as olivine ⇋ spinel. The second category involves reactions which occur within individual phases and includes solid solution, cation ordering, displacive transitions, magnetic transitions, etc. Because the energy changes for the two types of processes are commonly on a similar scale, internal effects can have a profound influence on how the equilibrium boundaries for the heterogeneous reactions are distributed in PT space. For example, the stability field of cordierite with respect to enstatite + sillimanite + quartz is considerably reduced if the cordierite has a disordered, rather than an ordered distribution of Al and Si between tetrahedral sites (Figure 5.1(a), from Putnis and Holland, 1986. Similarly, the aragonite ⇋ calcite phase boundary shows a marked curvature at least in part due to the orientational disordering of CO3 groups in calcite (Figure l(b), from Redfern et al, 1989. At the same time, there has been an increasing awareness among physicists that structural phase transitions in minerals show characteristic properties worthy of investigation from a purely solid-state-physics point of view. There is a confluence of interests, therefore, which has resulted in a new approach to the thermodynamic analysis of phase transitions in minerals based on Landau theory.
36 citations
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TL;DR: In this article, sufficient conditions for the existence and uniqueness of global solutions for the initial-value problem of the generalized 2D Ginzburg-Landau equation are obtained, which rigorously establishes the foundation for further investigation of this type of model.
36 citations
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01 Sep 1987TL;DR: The phase transition is accompanied by singularities of the elastic constants, leading to an elastic softening of the crystal structure as mentioned in this paper, which can be found in hexagonal, orthorhombic or monoclinic cordierite.
Abstract: Mg-cordierite undergoes a ferroelestic phase transitionP6/mmc-Cccm. The order parameterQ is proportional to the spontaneous strain as reflected by changes of the lattice parametersa andb during the phase transition. The order parameter,Q
od, which describes the Al, Si ordering, isnot directly involved in the phase transition and only “triggers” the structural collapse. Landau theory predicts that cordierite can exist in stable or metastable states with hexagonal, orthorhombic or monoclinic symmetry. Hexagonal cordierite can develop modulated structures which have been found by Putnis et al. (1987). The phase transition is predicted to be accompanied by singularities of the elastic constantsC
11,C
22 andC
12 leading to an elastic softening of the crystal structure.
36 citations
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TL;DR: In this paper, the crystal structure, the bulk magnetization characteristics and the magnetocaloric properties of Er1−xDyxCo2 compounds were investigated and a direct correlation was pointed out between the character of the magnetic transition and the behavior of the cell parameter versus x.
36 citations