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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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19 citations
TL;DR: In this paper, a comparative study of grain-size influence on the ferro-para phase transition and its thermal hysteresis was performed by recording the temperature dependence of the dielectric constant, heat capacity and pyrocharge.
Abstract: Ferroelectric barium titanate ceramics with grain sizes in the range (0.5, 20) µm were used for a comparative study of grain-size influence on the ferro-para phase transition and its thermal hysteresis. The investigations were performed by recording the temperature dependence of the dielectric constant, heat capacity and pyrocharge. The experimental results have been analysed in the framework of Landau-Devonshire theory. The grain-size dependent Landau coefficients of the free energy have been derived from our experimental data and used to compute the grain-size dependence of the theoretical transition interval related to the thermal hysteresis. The good qualitative agreement between theory and experiment recommends the size dependent Landau coefficients as a way to improve the modelling of the size dependent ferro-para phase transition in ceramics.
19 citations
TL;DR: In this paper, the Hartree and Thomas-Fermi methods and Landau theory for the ferroelectric transition were used to describe the core of the wall, whose width is typically similar to 10 nm.
Abstract: We consider the properties of charged domain walls in ferroelectrics as a quantum problem. This includes determination of self-consistent attracting 1D potential for compensating charge carriers, the number and positions of discrete energy levels in this potential, dependencies on the ferroelectric characteristics, as well as the spatial structure and formation energy of the wall. Our description is based on the Hartree and Thomas-Fermi methods and Landau theory for the ferroelectric transitions. Changeover from a few to many quantum levels (with the electron binding energies similar to 1 eV) is controlled by a single characteristic parameter. The quantum models well describe the core of the wall, whose width is typically similar to 10 nm. Additionally, the walls possess pronounced long-range tails which are due to trap recharging. For the trap concentration N-t = (10(17)-10(18)) cm(-3), the tail length l is of the mu m scale. On the distances much larger than l the walls are electrically uncoupled from each other and the crystal faces.
19 citations
TL;DR: In this article, the traditional derivation of the elastic anomalies associated with ferroelectric phase transitions in the framework of the Landau theory is combined with the piezoelectric constitutive relations instead of being explicitly carried out with a definite expression of the FE part of the free energy.
Abstract: The traditional derivation of the elastic anomalies associated with ferroelectric (FE) phase transitions in the framework of the Landau theory is combined with the piezoelectric constitutive relations instead of being explicitly carried out with a definite expression of the FE part of the free energy. In this manner it is shown that the softening within the FE phase is of electrostrictive and hence piezoelectric origin. Such a piezoelectric softening may be canceled by the better known piezoelectric stiffening, when the piezoelectric charges formed during the vibration are accompanied by the depolarization field, as for example in Brillouin scattering experiments. As experimental validation, we present new measurements on Zr-rich PZT, where the FE phase transforms into antiferroelectric on cooling or doping with La, and a comparison of existing measurements made on FE PZT with low frequency and Brillouin scattering experiments.
19 citations
TL;DR: In this article, a boundary condition for the Ginzburg-Landau wave function at surfaces biased by a strong electric field is derived within the de Gennes approach, which provides a simple theory of the field effect on the critical temperature of superconducting layers.
Abstract: A boundary condition for the Ginzburg-Landau wave function at surfaces biased by a strong electric field is derived within the de Gennes approach. This condition provides a simple theory of the field effect on the critical temperature of superconducting layers.
18 citations