CaTiSiO5, a titanite-type oxide, consists of one-dimensional chains of TiO6 octahedra bridged by SiO4 tetrahedra and CaO7 polyhedra. While
CaTiSiO5 has potential antiferroelectric properties, these have not been directly verified until now. In this study, we demonstrate the antiferroelectricity of CaTiSiO5 by observing a double P-E hysteresis loop. Moreover, we show an unconventional enhancement of permittivity through partial substitution of Si with Ge, resulting in a doubling of permittivity over a wide temperature range in the antiferroelectric phase. Transmission electron microscopy and second harmonic generation measurements have revealed the formation of microscopic polar regions in the antiferroelectric phase of CaTi(Si0.5Ge0.5)O5. Antiphase boundaries are suggested to play a role in the generation of these microscopic polar regions. This study provides new insights into boosting the permittivity of antiferroelectric materials from the perspective of domain engineering.

Surface tension phenomena in solids acquire significance at the nanoscale due to the pivotal influence on the elastic properties of the nanoscale systems. We demonstrate that the internal strains, produced by the surface tension in confined nanostructured ferroelectrics significantly affect the internal polarization distribution and show how the surface tension effects drive the topological transitions in ferroelectric nanoparticles and nanorods.

The potential for using domain walls as nanoscale interconnects in agile circuitry emerged as an exciting prospect along with the initial observations of enhanced domain wall conductivity over a decade ago. Furthermore, the ability to support p- and n-type transport within walls suggests the possibility to build p-n junctions that are comprised completely of domain wall material. However, measuring fundamental transport properties of domain walls has remained a challenge, in part due to complex wall morphologies, background bulk signals, and contact barrier effects. Here we present in-operando Kelvin Probe Force Microscopy based experiments which allow significant new insights into the carrier properties in domain walls in ErMnO₃ and to assess the feasibility of in-wall p-n junctions in LiNbO₃. In ErMnO₃, we confined current flow by cutting sub-micron thick slices of material and making separate contacts to the p- and n-type walls. Spatially resolved potential profiles associated with driving source-drain currents along the walls were measured, allowing barrier-free insights into the wall conduction mechanisms and estimates for domain wall conductivities to be made. To examine transport properties of domain wall p-n junctions, we use planar LiNbO₃ thin film devices, where such junctions arise along curved domain wall geometries. We find that the in-operando potential profiles measured along the walls can be fully rationalised through local variations in wall resistivity without the need to introduce any depletion zone contribution. We argue this is because the initial Fermi level differences usually associated with p-n junction behaviour in extrinsically doped p- and n-type semiconductors are absent. This is important for domain wall nanoelectronics, since it means domain wall p-n junctions are unlikely to exhibit diode behaviour or facilitate conventional transistor functionality. Finally, we also investigate the associated thermal transport properties of LiNbO₃ conducting domain walls using Scanning Thermal Microscopy to assess their potential use as heat flow conduits in thermal switches. It seems that any enhancement from electronic contributions to domain wall thermal transport seem to be minor, suggesting that the walls are likely to be more effective as phonon scatterers unless higher domain wall conductivities can be engineered.