Lithium zinc borohydride LiZn2(BH4)5 (LZBH) was investigated as a potentially interesting hydrogen storage material due to its high hydrogen content and low decomposition temperature. LZBH shows a structure of two identical interpenetrated three-dimensional frameworks with no bonds between them, which is a unique feature in complex metal hydrides. To better understand the relations between the structure and the thermodynamics of the system, we studied molecular dynamics in LZBH by means of 1H and 7Li NMR spectra and spin-lattice relaxation measurements. Different thermally activated reorientational processes of BH4 tetrahedra about their 2-fold and 3-fold symmetry axes were identified from the temperature-dependent proton and lithium spin−lattice relaxation rates and were quantified by their activation energies. Due to the structure, there are two different types of BH4 tetrahedra; one type is located between two Zn atoms and the other type between one Li and one Zn atom. Our study presents physical insight into the dynamic properties of LZBH on a microscopic level of atomic groups, providing link between the microscopic and the bulk properties of this phase.
COBISS.SI-ID: 27045671
As a continuation of the work on FeTe2O5X, X = Br, Cl system, Matej Pregelj, Andrej Zorko, Peter Jeglič, Zdravko Kutnjak, Simon Jazbec and Denis Arčon with coworkers studied magnetic, structural and dielectric properties of the FeTe2O5Cl compound. They have discovered that its ground state is multiferroic and that the corresponding magnetic ordering is very similar to the one in the isostructural FeTe2O5Br system. They also learned that the main difference between the two isostructural compounds is in the structural effects, accompanying the establishment of the multiferroic phase, which are in FeTe2O5Cl much more pronounced. Moreover, they assigned these structural changes to the shift of the O1 ion and correlated them with the polarization of the Te4+ lone-pair electrons. This way they confirmed that lone-pair electrons are indeed the carriers of the electric polarization in these systems.
COBISS.SI-ID: 27342375
By means of neutron scattering and specific heat measurements, Martin Klanjšek with French colleagues studied the magnetic ordering of quasi-one-dimensional antiferromagnet BaCo2V2O8 at low temperatures in the magnetic fields up to 12 T. They confirmed a theoretically predicted incommensurate magnetic ordering in fields above 3.9 T and showed that two types of magnetic domains with equal population develop in the material. They determined the critical exponents for the transitions into the Neél and incommensurate magnetic ordered state.
COBISS.SI-ID: 26539815
Substituted imidazole and benzimidazole often form polar hydrogen-bonded chains in the solid state. 2-Methylbenzimidazole is known to be a high-temperature organic ferroelectric. We have measured temperature dependences of 14N nuclear quadrupole resonance (NQR) frequencies and proton T1 in 2-methylbenzimidazole and 5,6-dimethylbenzimidazole. The NQR frequencies are assigned to amino and imino nitrogen positions. The NQR data exclude the possibility of proton two-site exchange in an N−H•••N hydrogen bond. The activation energies for the methyl group hindered rotation are determined in both compounds. The present 14N NQR data are compared to the published 14N NQR data in solid substituted and coordinated imidazoles, in substituted benzimidazoles and in imidazole in the gas phase. A linear correlation between the two inplane principal values of the quadrupole coupling tensor and the out-of plane principal value of the quadrupole coupling tensor is observed in imidazole, ranging from the amino nitrogen position to the imino nitrogen position. Transition from the amino to the imino nitrogen position is determined on the correlation diagram. The correlation diagram can be used to quantitatively observe the asymmetry of the N−H•••N hydrogen bond. A similar correlation diagram is proposed also for substituted benzimidazoles. The magnitudes of the principal values of the 14N quadrupole coupling tensor in ferroelectric 2-methylbenzimidazole show that the macroscopic ferroelectric ordering has in this compound a minor effect on the asymmetry of the N−H•••N hydrogen bonds.
COBISS.SI-ID: 2600804
Tungsten oxide nanostructures functionalized with gold or platinum NPs were synthesized and integrated, using a single-step method via aerosol-assisted chemical vapour deposition, onto micro-electromechanical system (MEMS)-based gas-sensor platforms. This co-deposition method is demonstrated to be an effective route to incorporate metal nanoparticles (NP) or combinations of metal NPs into nanostructured materials, resulting in an attractive way of tuning functionality in metal oxides. The results show variations in electronic and sensing properties of tungsten oxide according to the metal NPs introduced, which are used to discriminate effectively analytes (C2H5OH, H2, and CO) that are present in proton-exchange fuel cells. Improved sensing characteristics, in particular to H2, are observed at 250 °C with Pt-functionalized tungsten oxide films.
COBISS.SI-ID: 26176551