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Dynamic Disorder (dynamic + disorder)
Selected AbstractsChemInform Abstract: Dynamic Disorder of Bi2+8 Clusters in the Plastic Phase (Bi8)3Bi[InI4]9.CHEMINFORM, Issue 32 2009Aron Wosylus Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Evidence of a phase transition of RbHCO3 from high-resolution solid-state 13C and 87Rb NMR by comparison with KHCO3MAGNETIC RESONANCE IN CHEMISTRY, Issue 4 2004Christophe Odin Abstract A variable-temperature high-resolution 13C and 87Rb solid-state NMR study of powder rubidium hydrogencarbonate, RbHCO3, is presented for the first time. At ambient temperature, RbHCO3 is formed by centrosymmetric dimers linked by hydrogen bonds, but almost no information is available on this compound concerning proton disorder and the low-temperature phase. However, potassium hydrogencarbonate, KHCO3, which has an isomorphic structure for the high temperature phase, was well studied: it undergoes a non-ferroic, non-ferroelectric phase transition at Tc = 318 K between two monoclinic structures. The protons are disordered in an asymmetric double-well potential in the low-temperature phase, and the double-well potential becomes symmetric in the high-temperature phase. By comparison with recent solid-state NMR experimental results on KHCO3, we show that RbHCO3 undergoes a phase transition at Tc , 245 K, and give evidence that the proton dynamic disorder in both compounds is very similar. Copyright © 2004 John Wiley & Sons, Ltd. [source] Ge-based skutterudites MPt4Ge12: A comparative 195Pt NMR studyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2010Michael Baenitz Abstract The new Ge-based skutterudites MPt4Ge12 are investigated by 195Pt NMR. They form with M,=,Ba, Sr, La, Ce, Pr, Nd, Sm, Eu, Th and U and in contrast to some pnictide skutterudites they remain metallic independent of the filler ion. Here we show that, consistent with the Korringa theory, the residual shift 195K(T,,,0) scales with the density of states N(EF) and with the electronic specific heat coefficient ,. For the heavy filler ions La and Th an unusual 195K(T) dependence was found which might be associated to the effect of dynamic disorder (rattling). For paramagnetic CePt4Ge12 a Curie,Weiss-like behaviour in both the shift 195K(T) and the bulk susceptibility ,(T) confirms the Ce3+ -4f1 -state at high temperatures. At low temperatures 195K(T) passes through a maximum at around 60,K and saturates below 10,K. This is interpreted being due to an unstable Ce valence, like, e.g. in CeSn3. Further evidence comes from the spin-lattice relaxation where 195(1/T1) starts to deviate from its low-temperature linear Korringa-type of behaviour at around 60,K. We discuss our findings in the context of a dense Kondo system with valence fluctuations. For the van-Vleck paramagnet SmPt4Ge12 at low-temperatures, surprisingly, the shift is of the same order as for CePt4Ge12. It also passes through a maximum but at much lower temperatures (,6,K). [source] Hopping transport in 1D chains (DNA vs.PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2004Abstract We discuss charge transport in one-dimensional organic solids (DNA and discotic liquid-crystalline glass (DLC)), focusing on the effects of static and dynamic disorder. In the presence of static disorder it can be shown that the temperature dependence of the low-field mobility is , , exp [,(T0/T)2], with characteristic temperature T0 depending on the scale of the energy distribution of localized states responsible for transport. In the case of both static and dynamic disorder the situation is different. We obtain a temperature independent mobility in our molecular dynamics calculations in the case of large static and dynamic disorder compared to the energy overlap integral between the neighbouring sites. The theoretical results are in good agreement with experimental data. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Orientational disorder and phase transitions in crystals of dioxofluoromolybdate, (NH4)2MoO2F4ACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2010Anatoly A. Udovenko Dioxotetrafluoromolybdate, (NH4)2MoO2F4, was synthesized in a single-crystal form and its structures [(I) at 297,K and (II) at 223,K] were determined by X-ray diffraction. Two independent states of a cis -MoO2F4 octahedron are characteristic of static and dynamic disorder in structure (I). The dynamically disordered Mo atom is displaced from the symmetry axis producing four possible orientations of an anion that allow O and F atoms to be identified in separate orientations owing to the inherent differences between the Mo,O and Mo,F bonding. After the phase transition at lower temperature, (I) transforms into the statically disordered structure (II) with three possible orientations of the cis -MoO2F4 octahedron. In this case, it also seemed possible to distinguish between O and F atoms on a local scale. H atoms of two independent NH4 groups in (II) which form bifurcated N,H...F(O) hydrogen bonds were localized. [source] Disorder in crystals of dioxofluorotungstates, (NH4)2WO2F4 and Rb2WO2F4ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2008Anatoly A. Udovenko Dioxotetrafluorotungstates (NH4)2WO2F4 [(I) at 297,K and (II) at 133,K] and Rb2WO2F4 (III) were synthesized in a single-crystal form and their structures were determined by X-ray diffraction. Two independent states of the cis -WO2F4 octahedron are characteristic of static and dynamic disorder in structure (I). Dynamically disordered W2 is displaced from the symmetry axis producing four possible orientations of anion that permits O and F atoms to be identified in separate orientations owing to the inherent differences between W,O and W,F bonding. After the phase transition at lower temperature (201,K), (I) transforms into the twin structure (II) with complete O/F ordering. Structure (III) is characterized by full O/F static disorder without any phase transitions at lower temperature. [source] Disorder in Ag7GeSe5I, a superionic conductor: temperature-dependent anharmonic structural studyACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2008Stéphanie Albert A temperature-dependent structural investigation of the substituted argyrodite Ag7GeSe5I has been carried out on a single crystal from 15 to 475,K, in steps of 50,K, and correlated to its conductivity properties. The argyrodite crystallizes in a cubic cell with the space group. The crystal structure exhibits high static and dynamic disorder which has been efficiently accounted for using a combination of (i) Gram,Charlier development of the Debye,Waller factors for iodine and silver, and (ii) a split-atom model for Ag+ ions. An increased delocalization of the mobile d10 Ag+ cations with temperature has been clearly shown by the inspection of the joint probability-density functions; the corresponding diffusion pathways have been determined. [source] | ||||||||||