Conductive domain walls (DWs) in ferroic oxides as device elements are a highly attractive research topic because of their robust and agile response to electric field. Charged DWs possessing metallic-type conductivity hold the highest promises in this aspect. However, their intricate creation, low stability, and interference with nonconductive DWs hinder their investigation and the progress toward future applications. Here, we find that conversion of the nominally neutral ferroelastic 90° DWs into partially charged DWs in Pb(ZrTi)O thin films enables easy and robust control over the DW conductivity. By employing transmission electron microscopy, conductive atomic force microscopy and phase-field simulation, our study reveals that charging of the ferroelastic DWs is controlled by mutually coupled DW bending, type of doping, polarization orientation and work-function of the adjacent electrodes. Particularly, the doping outweighs other parameters in controlling the DW conductivity. Understanding the interplay of these key parameters not only allows us to control and optimize conductivity of such ferroelastic DWs in the oxide ferroelectrics but also paves the way for utilization of DW-based nanoelectronic devices in the future.

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Ferroelectric orthorhombic lead metaniobate (PbNb 2 O 6 ) is known to be metastable with respect to the thermodynamically stable nonferroelectric rhombohedral polymorph. The hightemperature tetragonal to low temperature rhombohedral phase transition is reconstructive and thereby sluggish; ferroelectric PbNb 2 O 6 is obtained by quenching from the stable phase field of the tetragonal polymorph. We report on the stabilization of the ferroelectric tungsten bronze polymorphs of PbNb 2 O 6 by minor chemical substitution in the seriesThe high-temperature tungsten bronze polymorph is entropy stabilized with respect to the stable rhombohedral polymorph, and we propose that the tungsten bronze is further entropy stabilized by chemical substitution, reducing the transition temperature of the rhombohedral polymorph and further disfavoring the kinetics of the undesired phase transition. Optimized solid-state synthesis and processing to obtain dense ceramics were developed for the solid solutions, and the dielectric, ferroelectric, and piezoelectric properties of the PbNb 2 O 6 solid solutions are reported. Curie temperature is suppressed with chemical substitution in all the systems. Lattice cell parameters display systematic variation with composition, reducing the molar volume, and the lattice parameter ratio 2b/a with increasing degree of substitution, reflecting a suppression of the polarization along the (010) direction due to chemical substitution. The piezoelectric properties improved with increasing substitution level probably due to the ease of poling of the materials with lower T c . However, some improvements seen with 2% CaTiO 3 were not accompanied by T c decrease.

In this work, the full piezoelectric characterization of highenergy ball-milled (HEBM) (0.6)BiFeO 3 -(0.4)PbTiO 3 (HE-BF PT60/40) multiferroic magnetoelectric ceramics was performed. The whole set of piezoelectric, mechanical, and elastic coefficients was obtained. The results revealed piezoelectric coefficients, namely d 31 5 À41.6 Â 10 À12 m/V and g 31 5 À9.65 Â 10 À3 Vm/ N (at room temperature), as high as those of other commercial piezoceramics. In fact, HE-BFPT60/40 piezoceramics produced by HEBM showed three times higher piezoelectric coefficients than those previously reported for conventionally synthesized piezoceramics. The thermal stability of d 31 and g 31 piezoelectric coefficients near room temperature, as well as the weak ferromagnetic response of HE-BFPT60/40 samples, make the (0.6)BiFeO 3 -(0.4)PbTiO 3 multiferroic magnetoelectric ceramics potential candidates for applications in future multifunctional piezo-magnetic-electric devices.S. E. Trolier-McKinstry-contributing editor