Maria A. Kirsanova

Monoclinic polymorph of TaFeTe ₂ is composed of atomically thin layers separated by van der Waals gaps. The compound shows ferromagnetic cluster-glass behavior with perpendicular magnetic anisotropy.

Medium-nickel layered oxide (NMC) materials are widely adopted by cell manufacturers, as they provide higher energy density without compromising safety at high voltage. However, challenges such as poor rate capability and limited lifetime at higher cutoff voltages still hinder their broader application. Our analysis of vendor materials revealed that, among the multiple additives used to enhance performance, cobalt is also employed as a surface coating element by some vendors. This study demonstrates a simple process to achieve a cobalt-rich surface on the NMC cathode via an all-dry synthesis method, verified by X-ray Photoelectron Spectroscopy (XPS). Our Co-coated NMC samples achieve performance close to that of top-tier vendor samples that incorporate multiple coating additives. Transmission electron microscopy (TEM) further confirms the incorporation of cobalt on the surface of single-crystal Li _1+x (Ni _0.6 Mn _0.4 ) _1-x O ₂ . This work highlights the importance of a cobalt-rich surface, showing that minimal cobalt addition can significantly improve electrochemical performance at high cutoff voltages without requiring numerous additives.

We recently demonstrated that the dielectric permittivity of a single-layer SrTiO3 thin film decreases with increasing thickness, and that incorporation of intermediate AlFeO3 layers into an SrTiO3 /AlFeO3 heterostructure mitigates this suppression of dielectric properties. We proposed two temperature-dependent mechanisms that could contribute to this effect: thermal strain and the formation of polar nanoregions (PNRs). In this study, we used Raman spectroscopy to assess the possibility of PNR formation in single-layer SrTiO3 films (50 and 250 nm thick) and in a multilayer heterostructure 5×[50 nm SrTiO3 + 50 nm AlFeO3. Our results show that the spectra of SrTiO3-containing structures exhibit telltale signs of PNR formation: the presence of symmetry-forbidden first-order modes and an asymmetric shape of the TO2 mode.

We investigate electron transport and phase-breaking processes in thin titanium nitride (TiN) films of epitaxial quality. Previous studies show that a minute surface magnetic disorder significantly reduces the critical temperature (Tc) and broadens the superconducting transition as the film thickness and device size decrease. We measure electron dephasing rates via magnetoresistance from Tc to ∼4Tc in various-thickness TiN films. Electron dephasing occurs on the picosecond timescale and is nearly independent of temperature, differing from the expected inelastic scattering due to the electron–phonon and electron–electron interactions near Tc, which occur over a nanosecond timescale. We propose spin-flip scattering as a possible additional phase-breaking mechanism. The significant increase in the dephasing rate for the thinnest film indicates that magnetic disorder resides near the surface of naturally oxidized films. Our research suggests that magnetic disorder may be a significant contributor to RF dissipation in superconducting devices based on TiN.

THz spectroscopy reveals ferroelectric soft mode behavior in SrTiO₃/AlFeO₃ heterostructure compared to SrTiO₃ films. Intermediate AlFeO₃ layers prevent degradation of the intrinsic dielectric response of SrTiO₃ layers in the heterostructure.

The diverse functionalities of (oxy-)hydroxides, such as electrocatalytic activity of transition-metal oxy-hydroxides in the oxygen evolution reaction (OER) and ion exchange capabilities of layered double hydroxides (LDHs), continue to attract significant interest. However, these compounds are typically synthesized in aqueous solutions at room temperature, under hydrothermal conditions, or in mild vapor atmospheres. Here, we present a novel (oxy-)hydroxide synthesis technique called “vapor hydroxidation,” which is conducted in a highly concentrated water vapor atmosphere at elevated temperatures. Structural analysis revealed the formation of a new oxy-hydroxide, [Ba₂O_x(OH)_y]_0.55InO₂, with a misfit-layered structure, characterized by alternating incommensurate barium hydroxide bilayers and indium oxide blocks. Unlike known (oxy-)hydroxides, this oxy-hydroxide displays exceptional thermal stability, retaining hydroxide ions within its crystal structure up to approximately 700 °C. These features suggest promising potential for high-temperature proton conductivity, as demonstrated by an electrical conductivity of 5 × 10⁻⁴ S cm⁻¹ at 500 °C even under dry argon. Our “vapor hydroxidation” method thus opens up a new avenue for the development of proton-functional materials with unconventional chemical and electronic characteristics.