Electron trapping by neutral pristine ferroelectric domain walls in BiFeO3_3

First-principles calculations for pristine neutral ferroelectric domain walls in BiFeO$_3$ reveal that excess electrons are selectively trapped by the domain walls, while holes are only weakly attracted. Such trapped excess electrons may be responsible for the thermally activated electrical conductivity at domain walls observed in experiments. In the case of a periodic array of domain walls, the trapped excess electrons create a zigzag potential, whose amplitude depends on the electron concentration in the material and the domain-wall distance. The potential is asymmetric for 71{\deg} and 109{\deg} domain walls. This could modify the open-circuit voltage in a solar cell and hence influence the photoelectric effect in BiFeO$_3$

Zig-zag charged domain walls in ferroelectric PbTiO3_3

We report a theoretical investigation of a charged 180$^\circ$ domain wall in ferroelectric PbTiO$_3$, compensated by randomly distributed immobile charge defects. For this we utilize atomistic shell-model simulations and continuous phase-field simulations in the framework of the Ginzburg-Landau-Devonshire model. We predict that domain walls form a zig-zag pattern and we discuss its properties in a broad interval of compensation-region widths, ranging from a couple to over a hundred nanometers

A neutron diffuse scattering study of PbZrO₃ and Zr-rich PbZr_1-xTi_xO₃

A combined neutron diffuse scattering study and model analysis of the antiferroelectric crystal PbZrO3is described. Following on from earlier X-ray diffuse scattering studies, supporting evidence for disordering of oxygen octahedral tilts and Pb displacements is shown in the high-temperature cubic phase. Excess diffuse scattering intensity is found at theMandRpoints in the Brillouin zone. A shell-model molecular dynamics simulation closely reproduces the neutron diffuse scattering pattern. Both in-phase and antiphase tilts are found in the structural model, with in-phase tilts predominating. The transition between disordered and ordered structure is discussed and compared with that seen in Zr-rich PbZr1−xTixO3.</jats:p

Transition between large and small electron polaron at neutral ferroelectric domain walls in BiFeO3_3

Ferroelectric domain walls are planes within an insulating material that can accumulate and conduct charge carriers, hence the interaction of the domain walls with the charge carriers can be important for photovoltaic and other electronic applications. By means of first principles calculations we predict a transition from a large two-dimensional electron polaron to a small polaron at the domain walls at a critical electron density, with polaron signatures in optical absorption and photoluminescence. We find that large and small polarons at the domain walls create different absorption peaks within the band gap that are not present in the case of pristine domain walls. These are an extended Drude peak in the case of large electron or hole polarons and a narrow mid-gap peak in the case of the small electron polaron.Comment: The main finding of the article, the transition between a large and a small electron polaron as a function of the polaron density, is an artefact, which resulted from applying an unsuitable methodology for modeling diluted polarons. This affects results depicted in Figs. 3, 4, 5, and

Polarized hyper-Raman scattering study of the silent F2u mode in PbMg1/3Nb2/3O3

International audienceA single crystal of the relaxor PbMg1/3Nb2/3O3 is studied by hyper-Raman scattering. The relative scattering intensities obtained for the band near 250 cm-1 in various polarization geometries are fully compatible with hyper-Raman spectroscopy tensor of the F2u zone-center vibrational mode of prototype Pm3¯m Oh 1 cubic perovskite structure. The mode was investigated between room temperature and 775 K, thus covering the range around the Burns temperature Td and the crossover temperature T. At variance with recent anticipations, no softening was observed

PMN relaxor: Hyper-Raman Scattering

In the past few years, we have tried to employ the Hyper'Raman Scattering technique in the investigations of the prototype relaxor crystal ' lead magnoniobate, PMN. This nonlinear technique is usually applicable only in the paralecric phase of ferroelectric substances, but is is often quite conveninent as the Hyper'Raman selection rules allways allow scattering by polar modes. In case of realoxors, investigations can be pursued well below the Burns temperature. Recently, the technique has been sucessfully applied to the investigation of the soft polar mode. We shall demonstrate that the lowest'frequency polar mode observed is the \"primary\" polar soft mode of PMN, responsible for the Curie'Weiss behavior of its dielectric permittivity above the Burns temperature