Search

Domain wall movement at and near engineered 10°, 15°, and 24° tilt and 10° and 30° twist grain boundaries was measured by band excitation piezoresponse force microscopy for Pb(Zr,Ti)O3 films with Zr/Ti ratio of 45/55 and 52/48. A minimum in nonlinear response was observed at the grain boundary for the highest angle twist and tilt grain boundaries, while a maximum in nonlinear response was observed at the 10° tilt grain boundaries. The observed nonlinear response was correlated with the domain configurations imaged in cross section by transmission electron microscopy. [ABSTRACT FROM AUTHOR]

Recently, there has been considerableinterest in the perovskitephase Na0.5Bi0.5TiO3(NBT) as a promisinglead-free piezoelectric material. Here we report low levels of Nanonstoichiometry (±2 atom % on the A-site) in the nominal startingcomposition of NBT ceramics can lead to dramatic changes in the magnitudeof the bulk (grain) conductivity (σb) and the conductionmechanism(s). Nominal starting compositions with Na excess exhibithigh levels of oxide-ion conduction with σb∼2.2 mS cm–1at 600 °C and an activation energy(Ea) < 1 eV whereas those with Na deficiencyare dielectrics based on intrinsic electronic conduction across theband gap with σb∼ 1.6 μS cm–1at 600 °C and Ea∼ 1.7 eV.Drying of reagents, especially Na2CO3, changesthe starting stoichiometry slightly due to a small amount of adsorbedmoisture in the raw materials but influences significantly the electricalproperties. This demonstrates the bulk electrical properties of NBTto be highly sensitive to low levels of A-site nonstoichiometry andreveals how to fine-tune the nominal starting composition of NBT ceramicsto suppress leakage conductivity for piezoelectric and high temperaturecapacitor applications. [ABSTRACT FROM AUTHOR]

Epitaxial tetragonal 425 and 611 nm thick Pb(Zr0.45Ti0.55)O3 (PZT) films are deposited by pulsed laser deposition on SrRuO3-coated (100) SrTiO3 24° tilt angle bicrystal substrates to create a single PZT grain boundary with a well-defined orientation. On either side of the bicrystal boundary, the films show square hysteresis loops and have dielectric permittivities of 456 and 576, with loss tangents of 0.010 and 0.015, respectively. Using piezoresponse force microscopy (PFM), a decrease in the nonlinear piezoelectric response is observed in the vicinity (720-820 nm) of the grain boundary. This region represents the width over which the extrinsic contributions to the piezoelectric response (e.g., those associated with the domain density/configuration and/or the domain wall mobility) are influenced by the presence of the grain boundary. Transmission electron microscope (TEM) images collected near and far from the grain boundary indicate a strong preference for (101)/( [ABSTRACT FROM AUTHOR]

WO3−x nanorods were grown on the tips of electrochemical etched W filaments by in-situ heating under different growth conditions. This kind of nanorods has the average diameter of 20 nm and the length of 1–2 μm. Transmission-electron microscopy investigations indicate that the sub-stoichiometric WO3 nanorods, prepared at about 830 °C under the atmosphere of H2 and Ar mixture, could grow along the either 〈0 0 1〉 or 〈1 1 0〉 direction with evident stacking faults and textural structure. Nanorods prepared without H2 atmosphere are found to be respectively W18O49 grown at around 900 °C and WO2.9 grown at 800 °C. [Copyright &y& Elsevier]

We report the results of polarization‐dependent Raman spectroscopy of phonon states in single‐crystalline quasi‐one‐dimensional NbTe4 and TaTe4 van der Waals materials. The measurements were conducted in the wide temperature range from 80 to 560 K. Our results show that although both materials have identical crystal structures and symmetries, there is a drastic difference in the intensity of their Raman spectra. While TaTe4 exhibits well‐defined peaks through the examined wavenumber and temperature ranges, NbTe4 reveals extremely weak Raman signatures. The measured spectral positions of the phonon peaks agree with the phonon band structure calculated using the density‐functional theory. We offer possible reasons for the intensity differences between the two van der Waals materials. Our results provide insights into the phonon properties of NbTe4 and TaTe4 van der Waals materials and indicate the potential of Raman spectroscopy for studying charge‐density‐wave quantum condensate phases. [ABSTRACT FROM AUTHOR]

Polycrystalline phase-pure Na0.5Bi0.47Sr0.02TiO2.975 is prepared by calcination of appropriate amounts of Na2CO3, Bi2O3, TiO2, and SrCO3 (800 °C, 2 h) followed by ball milling, pelletizing, and final annealing (1150 °C, 2 h). [ABSTRACT FROM AUTHOR]

Researchers have demonstrated that BiFeO3 exhibits ferroelectric hysteresis but none have shown a strong ferromagnetic response in either bulk or thin film without significant structural or compositional modification. When remanent magnetisations are observed in BiFeO3 based thin films, iron oxide second phases are often detected. Using aberration-corrected scanning transmission electron microscopy, atomic resolution electron energy loss spectrum-mapping and quantitative energy dispersive X-ray spectroscopy analysis, we reveal the existence of a new Fe2O3-rich perovskite nanophase, with an approximate formula (Fe0.6Bi0.25Nd0.15)3+ Fe3+O3, formed within epitaxial Ti and Nd doped BiFeO3 perovskite films grown by pulsed laser deposition. The incorporation of Nd and Bi ions on the A-site and coherent growth with the matrix stabilise the Fe2O3-rich perovskite phase and preliminary density functional theory calculations suggest that it should have a ferrimagnetic response. Perovskite-structured Fe2O3 has been reported previously but never conclusively proven when fabricated at high-pressure high-temperature. This work suggests the incorporation of large A-site species may help stabilise perovskite-structured Fe2O3. This finding is therefore significant not only to the thin film but also to the high-pressure community. [ABSTRACT FROM AUTHOR]

Sr0.95Ce0.05CoO3-δ (I) and Sr0.9Ce0.1CoO3-δ (II) are prepared by sol-gel reaction of Sr(NO3)2, Co(NO3)2, and Ce(NO3)3 in citric acid and ethylene glycol (353 K, 10 h) followed by gel drying and calcination in air (1373 K, 5 h). [ABSTRACT FROM AUTHOR]

A correction to the article "Influence of a Single Grain Boundary on Domain Wall Motion in Ferroelectrics" that was published in a 2014 issue is presented.

S. Trolier‐McKinstry and co‐workers investigate the interaction between domain walls and a single grain boundary by comparing measurements of the local piezoelectric nonlinearity to domain structure. The two electron micrographs show the domain structure of the film, while the colored image is a map of the piezoelectric nonlinear response across a single grain boundary in a ferroelectric film. A minimum in the nonlinearity observed at the grain boundary is correlated to a change in the domain structure. [ABSTRACT FROM AUTHOR]

We report the polarization-dependent Raman spectra of exfoliated MoI3, a van der Waals material with a "true one-dimensional" crystal structure that can be exfoliated to individual atomic chains. The temperature evolution of several Raman features reveals an anomalous behavior suggesting a phase transition of magnetic origin. Theoretical considerations indicate that MoI3 is an easy-plane antiferromagnet with alternating spins along the dimerized chains and with inter-chain helical spin ordering. The calculated frequencies of phonons and magnons are consistent with the interpretation of the experimental Raman data. The obtained results shed light on the specifics of the phononic and magnonic states in MoI3 and provide a strong motivation for further study of this unique material with potential for future spintronic applications. [ABSTRACT FROM AUTHOR]

Abstract: Hard carbon spherules (HCS) were used as support of Pt nanoparticles as electrocatalyst for direct methanol fuel cells (DMFCs). Scanning electron microscopy (SEM) images show that the size of the Pt particles on HCS by reduction of K2PtCl6 with ethylene glycol is 4–5nm. High-resolution transmission electron microscopy (HRTEM) study reveals that the Pt particles on the HCS surface have faceted crystalline structures. The size and aggregation of the Pt particles depend on the surface properties of the carbon support and the medium of the reduction reaction. Cyclic voltammetry and galvanostatic polarization experiments show that the Pt/HCS catalyst exhibits a higher catalytic activity in the electrooxidation of methanol than either the Pt/MCMB or the commercial Pt/Vulcan XC-72 catalyst does. [Copyright &y& Elsevier]

A dielectric bulk glass-ceramic of the La 2 O 3 –TiO 2 –SiO 2 –B 2 O 3 system is developed which is able to fulfill the requirements for dielectric loading-based mobile communication technologies. It is shown that the given dielectric requirements can be fulfilled by glass-ceramic materials without being dependent on ceramic processing techniques. The material exhibited permittivity values of 20 < ɛ r < 30, quality factor 2000 GHz < Qf < 10,000 GHz and a temperature coefficient of resonance frequency −100 < τ f < +180 ppm/K. A zero τ f material with a Qf value of 9500 GHz and ɛ r = 21.4 could be achieved at a ceramming temperature T cer = 870 °C. The material is aimed to provide an alternative to existing, commercially used sintered ceramic materials. Further focus is laid on the investigation of the dominant dielectric loss mechanisms in the GHz frequency range and how they are correlated with the microstructure. [ABSTRACT FROM AUTHOR]

High-Mn austenitic steels, usually deformed via the TWIP (twinning induced plasticity) mechanism, suffer high cost and other technical issues (e.g., hot-dip galvanizing, welding, etc.) from the high Mn content. Nevertheless, decreasing the Mn content would result in a shift of deformation mechanisms from TWIP to TRIP (transformation induced plasticity), usually causing quasi-cleavage brittle fracture. Herein, we report that by massive nanoprecipitation of coherent disordered particles, the grain sizes of a near medium Mn austenitic steel are successfully refined to 0.9 ± 0.4 μ m, leading to a significant stacking fault energy increment of 6.4–7.9 mJ m–2 and accordingly, the transition of deformation mechanism from TRIP to multiple deformation mechanisms, namely, stacking faults, dislocation slip, nanotwinning and ԑ-martensite transformation. Moreover, the high-density of coherent nanoprecipitates effectively refines ԑ martensite and nanotwins from 20–500 nm and 10–50 nm to a few atomic columns and 1–15 nm, respectively. More importantly, these deformation mechanisms were sequentially activated at different deformation stages, resulting in a consistently high work hardening rate. Based on the synergistic refinement effects of grains, twins and martensite and the transition of deformation mechanism, a near medium Mn ultrafine-grained (UFG) austenitic steel with 15 wt.% Mn is developed, which shows a unique combination of high tensile strength (1210 ± 19 MPa) and large elongation (72 ± 6 %). These findings provide a new route to addressing the trade-off between the Mn content and mechanical performance of high-Mn austenitic steels which could facilitate their widespread applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Oxide ion conductors find important technical applications in electrochemical devices such as solid-oxide fuel cells (SOFCs), oxygen separation membranes and sensors. Na0.5Bi0.5TiO3 (NBT) is a well-known lead-free piezoelectric material; however, it is often reported to possess high leakage conductivity that is problematic for its piezo- and ferroelectric applications. Here we report this high leakage to be oxide ion conduction due to Bi-deficiency and oxygen vacancies induced during materials processing. Mg-doping on the Ti-site increases the ionic conductivity to ~0.01 S cm−1 at 600 °C, improves the electrolyte stability in reducing atmospheres and lowers the sintering temperature. This study not only demonstrates how to adjust the nominal NBT composition for dielectric-based applications, but also, more importantly, gives NBT-based materials an unexpected role as a completely new family of oxide ion conductors with potential applications in intermediate-temperature SOFCs and opens up a new direction to design oxide ion conductors in perovskite oxides. [ABSTRACT FROM AUTHOR]