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Doping with various cations is considered to be a key method for inducing ferroelectricity in HfO2. However, previous studies often neglected the role of carriers introduced by heterovalent dopants. Here, using first-principles calculations, we show that carriers profoundly affect the stability of polar phases and advocate that carriers should be considered as a fundamental framework for understanding the origin of ferroelectricity in doped HfO2. Although doping with p-type elements that introduce holes can stabilize the polar phase, it is not sufficient to make them the ground state phase. However, when they are co-doped with an n-type V element, they not only stabilize the polar phase to the ground state, but also achieve charge neutrality through electron compensation. This is due to the formation of deep energy levels (electron–hole recombination centers) by V doping, similar to oxygen vacancies. Unlike oxygen vacancy compensation, which favors the formation of tetragonal phases, co-doping is more favorable for the formation of polar phases and the absence of structural defects. Our results contribute to the understanding of the origin of HfO2 ferroelectricity and provide a potential method for the preparation of HfO2-based films with excellent ferroelectric properties. [ABSTRACT FROM AUTHOR]

Chronic wound healing remains challenging due to the oxidative microenvironment. Prussian blue (PB) nanoparticles exhibiting multiple antioxidant enzyme-like activities have attracted widespread attention, while their antioxidant efficacy remains unsatisfied. Herein, ultrasmall calcium-enriched Prussian blue nanoparticles (CaPB NPs) are simply constructed with high yields for the wound repair application. Owing to the ultrasmall size and synergistic effect of the generated dual active sites, the CaPB NPs exhibit prominent antioxidase-like activities, protecting cells from oxidative stress-induced damage. In addition to the effect of Ca on regulating keratinocyte and fibroblast growth, it has been demonstrated that the administration of CaPB NPs obviously promoted wound closure as well as collagen deposition and neovascularization in the full-thickness wound defect model in mice. Importantly, the CaPB NP treatment can effectively up-regulate the expression levels of anti-inflammatory cytokines and vascular endothelial growth factors to remodel the wound microenvironment, thereby accelerating the wound healing process. Overall, this work reveals that metal atom substitution is an effective strategy to construct ultrasmall and high-catalytic-performance PB-based nanozymes and further potentiate their effectiveness for chronic wound management. [ABSTRACT FROM AUTHOR]

A structurally simple, highly reactive chlorinating reagent, N-chloro-N-fluorobenzenesulfonylamine (CFBSA), was conveniently prepared from inexpensive Chloramine B in high yield. A wide range of substrates were chlorinated with it to obtain products in good to high yields and appropriate selectivity. [ABSTRACT FROM AUTHOR]

Bimetallic Pt@Ir zigzag nanocomplexes were successfully synthesized with a uniform morphology via the simple reduction of Ir(acac)3 on the surface of Pt nanorods. The novel Pt@Ir nanocomplexes exhibited good catalytic activity in hydrogenation reactions under mild conditions, such as the hydrogenation of nitroaromatic compounds. The highest yield of the obtained product achieved was ∼99.9% using H2 as the sole reductant. [ABSTRACT FROM AUTHOR]

Multiferroic composite thin films were fabricated based on ferroelectric (FE) Bi3.15Nd0.85Ti3O12 (BNT) and ferromagnetic (FM) La0.7Ca0.3MnO3 (LCMO) parents with different growth sequences of BNT–LCMO/LNO/STO (BL) and LCMO–BNT/LNO/STO (LB). Ferroelectric behaviour along with remnant polarization (2Pr) of 50 μC cm2 and 40 μC cm2 at room temperature, saturated magnetization values around 206 emu cm−3 and 192 emu cm−3 at 100 K were measured for BL and LB composite films, respectively. The temperature dependence of the magnetoelectric (ME) coupling effect was investigated and the ME voltage coefficients of 63 mV cm−1 Oe−1 and 60 mV cm−1 Oe−1 at 100 K were respectively obtained for the BL and LB films. The results show that the composite films exhibit both good ferroelectric and ferromagnetic properties, as well as a substantial ME effect. Moreover, it is demonstrated that the layer sequences and temperature have significant impacts on the magnetoelectric coupling behaviour of these double-layered thin films, which is very likely caused by the magnetic–mechanical–electric interaction, substrate clamping and interface coupling. [ABSTRACT FROM AUTHOR]

We present a kinetic model to investigate the anomalous thermal conductivity in silicon nanowires (SiNWs) by focusing on the mechanism of phonon–boundary scattering. Our theoretical model takes into account the anharmonic phonon–phonon scattering and the angle-dependent phonon scattering from the SiNWs surface. For SiNWs with diameter of 27.2 nm, it is found that in the case of specular reflection at lateral boundaries, the thermal conductivity increases as the length increases, even when the length is up to 10 μm, which is considerably longer than the phonon mean free path (MFP). Thus the phonon–phonon scattering alone is not sufficient for obtaining a normal diffusion in nanowires. However, in the case of purely diffuse reflection at lateral boundaries, the phonons diffuse normally and the thermal conductivity converges to a constant when the length of the nanowire is greater than 100 nm. Our model demonstrates that for observing the length dependence of thermal conductivity experimentally, nanowires with smooth and non-contaminated surfaces, and measuring at low temperature, are preferred. [ABSTRACT FROM AUTHOR]

Polar metals, commonly defined by the coexistence of polar structure and metallicity, are thought to be scarce because free carriers eliminate internal dipoles that may arise owing to asymmetric charge distributions. By using first-principle electronic structure calculations, we explored the possibility of producing metallic states in the polar/nonpolar KNbO 3 /BaTiO 3 superlattice (SL) composed of two prototypical ferroelectric materials: BaTiO 3 (BTO) and KNbO 3 (KNO). Two types of polar/nonpolar interfaces, p-type (KO) - /(TiO 2 ) 0 and n-type (NbO 2 ) + /(BaO) 0 , which can be constituted into two symmetric NbO 2 /BaO-NbO 2 /BaO (NN-type) and KO/TiO 2 -KO/TiO 2 (PP-type) SL, as well as one asymmetric KO/TiO 2 -NbO 2 /BaO (PN-type) SL. The spatial distribution of ferroelectric distortions and their conductive properties are found to be extraordinarily sensitive to the interfacial configurations. An insulator-to-metal transition is found in each unit cell of the symmetric interfacial SL models: one exhibiting quasi-two-dimensional n-type conductivity for NN-type SL, while the other being quasi-two-dimensional p-type conductivity for PP-type SL. The anisotropic coexistence of in-plane orientation of free carriers and out-of-plane orientation of ferroelectric polarization in KNO/BTO SL indicates that in-plane free carriers can not eliminate the out-of-plane dipoles. Our results provide a road map to create two-dimensional polar metals in insulating perovskite oxide SL, which is expected to promote applications of new quantum devices., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

A cooperative thermal decomposition route to large-scaled star-shaped α-MnS nanocrystals, which show novel magnetic properties, i.e., a high blocking temperature (275 K) and a large coercive field (1573 Oe), is reported.