Translational Antiphase Boundaries in NaNbO3 Antiferroelectrics

Planar defects are known to be of importance in affecting the functional properties of materials. Translational antiphase boundaries (APBs) in particular have attracted considerable attention in perovskite oxides, but little is known in lead-free antiferroelectric oxides that are promising candidates for energy storage applications. Here, we present a study of translational APBs in prototypical antiferroelectric NaNbO3 using aberration-corrected (scanning) transmission electron microscopy (TEM) techniques at different length scales. The translational APBs in NaNbO3 are characterized by a 2-fold-modulated structure, which is antipolar in nature and exhibits a high density, different from the polar nature and lower density in PbZrO3. The high stability of translational APBs against external electric fields and elevated temperatures was revealed using ex situ and in situ TEM experiments and is expected to be associated with their antipolar nature. Density functional theory calculations demonstrate that translational APBs possess only slightly higher free energy than the antiferroelectric and ferroelectric phase energies with differences of 29 and 33 meV/f.u., respectively, justifying their coexistence down to the nanoscale at room temperature. These results provide a detailed atomistic elucidation of translational APBs in NaNbO3 with antipolar character and stability against external stimuli, establishing the basis of defect engineering of antiferroelectrics for energy storage devices.

Tailoring Optical Properties in Transparent Highly Conducting Perovskites by Cationic Substitution

SrMoO₃ , SrNbO₃ , and SrVO₃ are remarkable highly conducting d¹ (V, Nb) or d² (Mo) perovskite metals with an intrinsically high transparency in the visible. A key scientific question is how the optical properties of these materials can be manipulated to make them suitable for applications as transparent electrodes and in plasmonics. Here, it is shown how 3d/4d cationic substitution in perovskites tailors the relevant materials parameters, i.e., optical transition energy and plasma frequency. With the example of the solid-state solution SrV_{1- x} Mo_x O₃ , it is shown that the absorption and reflection edges can be shifted to the edges of the visible light spectrum, resulting in a material that has the potential to outperform indium tin oxide (ITO) due to its extremely low sheet resistance. An optimum for x = 0.5, where a resistivity of 32 µΩ cm (≈12 Ω sq^-1 ) is paired with a transmittance above 84% in the whole visible spectrum is found. Quantitative comparison between experiments and electronic structure calculations show that the shift of the plasma frequency is governed by the interplay of d-band filling and electronic correlations. This study advances the knowledge about the peculiar class of highly conducting perovskites toward sustainable transparent conductors and emergent plasmonics.

Quantum Mechanical Screening of 2D MBenes for the Electroreduction of CO2 to C1 Hydrocarbon Fuels

In this work, we propose a new family of two-dimensional (2D) transition metal borides (MBenes) to design and explore new high-efficiency catalysts for CO₂ electroreduction according to the Density Functional Theory (DFT) approach. The recently reported MBenes have been synthesized experimentally and have been found to have high electrical conductivities and stability, so they are promising candidates for the development of CO₂ electrocatalytic reduction (RR) catalysts. However, tuning the reaction mechanism such that the production of hydrocarbon species occurs at a low overpotential remains a challenge. Only C1 hydrocarbon products such as CH₄, CH₃OH, HCHO, CO, and HCOOH were identified, indicating that these MBenes have high stability, catalytic activity, and selectivity toward CO₂ reduction and overcome the competing hydrogen evolution reaction (HER). These MBenes possess a metallic feature that can be tuned as a new catalyst for CO₂RR, depending on the ability to control their selectivity and catalytic activity.