Easy axis antiferromagnets usually exhibit a first order spin-flop transition when the magnetic field is applied along the easy axis. Recently a colossal magnetoelectric effect was discovered in Ni3TeO6, suggesting a continuous spin-flop transition across a narrow phase in this material [Y. S. Oh, et al., Nature Comm. 5, 3201 (2014)]. Additional evidence is, however, desirable to verify this mechanism. Here we measure the infrared vibrational properties of Ni3TeO6 in high magnetic fields and demonstrate that the phonon anomalies are consistent with a second-order mechanism.

We have investigated the diffusion dynamics of protons in hydrated 4.2% Ca-doped LaPO 4 , a candidate electrolyte for proton-conducting intermediate temperature fuel cells. The macroscopic and microscopic dynamics have been studied using electrochemical impedance spectroscopy (EIS) and quasi-elastic neutron scattering (QENS), respectively. The conductivity of the bulk hydrated sample was determined in the temperature range of 500−850 °C by EIS and showed a clear signature of proton conductivity with an activation energy of about 1.0 eV. The QENS experiment revealed a fast dynamical process below 500 °C that was not observed by EIS. The activation energy of the fast proton diffusion is 0.09 eV in the temperature range from 150 °C to 500 °C.

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We investigated the crystal structure, defect structure, and thermal stability of the rare-earth phosphate proton conductors (La,M)PO 4 (where M = Sr, Ca) and obtained the thermal expansion coefficients, surface topography, size distribution, and proton conductivity. The study employed neutron powder diffraction (NPD) at elevated temperatures up to 800 °C, combined with powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). Although the proton-oxygen site is located on the corners of the PO 4 tetrahedra, the NPD shows an average bond length distortion in the hydrated 4.2% Sr/Ca-doped LaPO 4 . We investigated the proton dynamics by EIS and previously by Quasi-Elastic Neutron Scattering (QENS), and determined the bulk diffusion and the self-diffusion coefficients. Our results showed that QENS and EIS probe fundamentally different proton diffusion processes, where the EIS data reflect long-range intertetrahedral diffusion, whereas QENS probes more local diffusive motions.

We measured the optical response of CuGeO3 nanorods in order to reveal size effects on the electronic properties. The vibronically-activated d-to-d color band excitations are activated by the 131 and 478 cm −1 phonons, with the relative contribution of the lower frequency O-Cu-O bending mode increasing with decreasing size until it dominates the process. We also uncover trends in the direct band gap, with the charge transfer transfer edge hardening with decreasing size. These findings advance the understanding of size effects in low-dimensional copper oxides.

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Development of a new radiometer for the thermodynamic measurement of high temperature fixed points AIP Conf. Proc. 1552, 65 (2013); 10.1063/1.4821372High-temperature and high-pressure pulsed synthesis apparatus for supercritical production of nanoparticles Rev. Sci. Instrum. 82, 084102 (2011) A design for a sample cell system suitable for high temperature Quasi-Elastic Neutron Scattering (QENS) experiments is presented. The apparatus was developed at the Spallation Neutron Source in Oak Ridge National Lab where it is currently in use. The design provides a special sample cell environment under controlled humid or dry gas flow over a wide range of temperature up to 950• C. Using such a cell, chemical, dynamical, and physical changes can be studied in situ under various operating conditions. While the cell combined with portable automated gas environment system is especially useful for in situ studies of microscopic dynamics under operational conditions that are similar to those of solid oxide fuel cells, it can additionally be used to study a wide variety of materials, such as high temperature proton conductors. The cell can also be used in many different neutron experiments when a suitable sample holder material is selected. The sample cell system has recently been used to reveal fast dynamic processes in quasi-elastic neutron scattering experiments, which standard probes (such as electrochemical impedance spectroscopy) could not detect. In this work, we outline the design of the sample cell system and present results demonstrating its abilities in high temperature QENS experiments. C 2015 AIP Publishing LLC. [http://dx

We bring together optical spectroscopy and first principles calculations to reveal the electronic properties of the chiral ferromagnet Fe 1/3 TaS2. Signatures of chirality are superimposed upon a complex free carrier response that emanates from both Ta and Fe bands. These include a honeycomb charge density pattern in the Fe layer and a hole → electron pocket crossover at the K-point, low energy excitations between spin split bands that cross the Fermi surface, and clustered rather than well-separated on-site and charge transfer excitations. These findings advance the understanding of intercalation and symmetry breaking on the fundamental excitations in metallic chalcogenides.