Impact of 3D Curvature on the Polarization Orientation in Non-Ising Domain Walls.

Ferroelectric domain boundaries are quasi-two-dimensional functional interfaces with high prospects for nanoelectronic applications. Despite their reduced dimensionality, they can exhibit complex non-Ising polarization configurations and unexpected physical properties. Here, the impact of the three-dimensional (3D) curvature on the polarization profile of nominally uncharged 180° domain walls in LiNbO3 is studied using second-harmonic generation microscopy and 3D polarimetry analysis. Correlations between the domain-wall curvature and the variation of its internal polarization unfold in the form of modulations of the Néel-like character, which we attribute to the flexoelectric effect. While the Néel-like character originates mainly from the tilting of the domain wall, the internal polarization adjusts its orientation due to the synergetic upshot of dipolar and monopolar bound charges and their variation with the 3D curvature. Our results show that curved interfaces in solid crystals may offer a rich playground for tailoring nanoscale polar states.

Potassium Ion Conductivity in the Cubic Labyrinth of a Piezoelectric, Antiferromagnetic Oxoferrate(III) Tellurate(VI).

Orange-colored crystals of the oxoferrate tellurate K12+6x Fe6 Te4-x O27 [x=0.222(4)] were synthesized in a potassium hydroxide hydroflux with a molar water-base ratio n(H2 O)/n(KOH) of 1.5 starting from Fe(NO3 )3 ⋅ 9H2 O, TeO2 and H2 O2 at about 200 °C. By using (NH4 )2 TeO4 instead of TeO2 , a fine powder consisting of microcrystalline spheres of K12+6x Fe6 Te4-x O27 was obtained. K12+6x Fe6 Te4-x O27 crystallizes in the acentric cubic space group I 4 ‾ 3d. [FeIII O5 ] pyramids share their apical atoms in [Fe2 O9 ] groups and two of their edges with [TeVI O6 ] octahedra to form an open framework that consists of two loosely connected, but not interpenetrating, chiral networks. The flexibility of the hinged oxometalate network manifests in a piezoelectric response similar to that of LiNbO3 .The potassium cations are mobile in channels that run along the <111> directions and cross in cavities acting as nodes. The ion conductivity of cold-pressed pellets of ball-milled K12+6x Fe6 Te4-x O27 is 2.3×10-4 S ⋅ cm-1 at room temperature. Magnetization measurements and neutron diffraction indicate antiferromagnetic coupling in the [Fe2 O9 ] groups.