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Mechanically compatible and electrically neutral domain walls in tetragonal, orthorhombic and rhombohedral ferroelectric phases of BaTiO3 are systematically investigated in the framework of the phenomenological Ginzburg-Landau-Devonshire (GLD) model with parameters of Ref. [Hlinka and Marton, Phys. Rev. 74, 104104 (2006)]. Polarization and strain profiles within domain walls are calculated numerically and within an approximation leading to the quasi-one-dimensional analytic solutions applied previously to the ferroelectric walls of the tetragonal phase [W. Cao and L.E. Cross, Phys. Rev. 44, 5 (1991)]. Domain wall thicknesses and energy densities are estimated for all mechanically compatible and electrically neutral domain wall species in the entire temperature range of ferroelectric phases. The model suggests that the lowest energy walls in the orthorhombic phase of BaTiO3 are the 90-degree and 60-degree walls. In the rhombohedral phase, the lowest energy walls are the 71-degree and 109-degree walls. All these ferroelastic walls have thickness below 1 nm except for the 90-degree wall in the tetragonal phase and the 60-degree S-wall in the orthorhombic phase, for which the larger thickness of the order of 5 nm was found. The antiparallel walls of the rhombohedral phase have the largest energy and thus they are unlikely to occur. The calculation indicates that the lowest energy structure of the 109-degree wall and few other domain walls in the orthorhombic and rhombohedral phases resemble Bloch-like walls known from magnetism.

There are two types of domain walls, O120 and R180{110}, for which the polarization profiles shown in Figs. 7 and 9(b) were not correctly calculated in the paper. 1 The polarization profiles were obtained numerically from constrained Euler-Lagrange equations. These equations can be written in the formwhere G rsrs , G rsts , and G tsts are components of the rotated gradient tensor. By mistake, G rsts terms were omitted in the paper. The correct profiles of polarization across the O120 and R180{110} domain walls, which do take into account the G rsts terms, are displayed here in Figs. 1 and 2. In all other domain walls considered in the paper, G rsts terms are zero for symmetry reasons. This Erratum does not affect any other result or the conclusion of the paper. FIG. 1. Trajectories of O120 (a) and R180{110} (b) domain walls superimposed with corresponding Euler-Lagrange energy surfaces. These two panels should replace the corresponding panels in the Fig. 7 of the paper. FIG. 2. Polarization profiles across the R180{110} domain wall, which should replace Fig. 9(b). 1 P. Marton, I. Rychetsky, and J. Hlinka, Phys. Rev. B 81, 144125 (2010). 139906-1

The dielectric dispersion of the transparent relaxor ferroelectric ceramics PLZT 8/65/35 and 9.5/65/35 was determined in a wide frequency range including the microwave and infrared range. The number of observed polar phonons in infrared spectra gives evidence about the locally broken cubic symmetry and the presence of polar nanoclusters in the whole investigated temperature range up to 530 K. A single broad and symmetric dispersion that occurs below the polar phonon frequencies was fitted with the Cole-Cole formula and a uniform distribution of Debye relaxations. On decreasing temperature, the distribution of relaxation times becomes extremely broad which indicates increasing correlation among the clusters. The mean relaxation time diverges according to the Vogel-Fulcher law with the same freezing temperature 230±5 K for both ceramics, but different activation energies 1370 K and 1040 K for the 8/65/35 and 9.5/65/35 sample, respectively. The shortest relaxation time is about 10-12 s and remains almost temperature independent. Below room temperature, the loss spectra become essentially frequency independent and the permittivity increases linearly with decreasing logarithm of frequency. The slope of this dependence is proportional to T  4 in the investigated temperature range (above 210 K) which indicates appreciable anharmonicity of the potential for polarization fluctuations.

The depolarization fields play an important role in terahertz experiments on nanostructured samples with complex nanoparticle morphologies and percolation pathways. Namely, their effects can hide or distort peculiarities of nanoscopic charge transport in the spectra measured on these structures. We calculate the local fields for a large number of percolated and non-percolated two-dimensional model structures by numerical solving of Maxwell equations in the quasi-static limit. The results strongly suggest that in a broad family of structures a simple effective medium approximation model can be applied to characterize the effective response. The model consists in an equivalent circuit composed of a resistance accounting for the percolated chains with an additional parallel RC-branch describing the non-percolated part. The physical meaning of this model is discussed in the frame of the Bergman spectral representation of effective medium. We show a recipe for the retrieval of a response connected to the depolarization fields and to the nanoscale transport mechanisms from transient terahertz spectra. Finally, we use the model to interpret our THz photoconductivity spectra in various TiO films with nanofabricated percolation pathways.

Dielectric properties of the relaxor ferroelectric ceramics PLZT 8/65/35 and 9.5/65/35 were studied in the broad frequency range of 100 Hz-1 THz at low temperatures below the freezing temperature. Nearly frequency-independent dielectric losses were observed up to 1 GHz on cooling down to 10 K. Their magnitude decreases exponentially with temperature, but remains remarkable high down to 10 K. A Landau-type thermodynamic model based on the perovskite structure near the morphotropic phase boundary is proposed for calculating the energy barriers for polarization reversal near the polar cluster boundaries and explaining the broad distribution function of relaxation times, which fits the observed frequency dependences of permittivity and losses below 1 GHz. High dielectric losses in the submillimetre region were explained by shear wave emission of vibrating polar cluster walls in an ac electric field and by piezoelectric resonances on polar clusters.

Assessment of characteristic length and time scales of the charge localization in nanostructured semiconductors is a key point for understanding the initial stage of carrier transport after photoexcitation. A concerted use of time-resolved terahertz spectroscopy and Monte Carlo simulations of the motion of confined electrons allow us to obtain this information and develop a quantitative microscopic model of the electron transport in a nanocrystalline CdS film. A weak localization is observed inside individual nanocrystals while much stronger localization stems from the existence of nanocrystal clusters partially surrounded by voids. The efficiency of the short-range transport is controlled by the excess energy of electrons: Its increase enhances the conductive coupling between adjacent nanocrystals and clusters. Relaxation of electrons with high excess energy then leads to a decrease of their mobility on a subpicosecond time scale. Filling of conduction-band states by increasing the optical pump fluence allows us to maintain a high level of conductive coupling even at later times.

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