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The structure of a series strontium vanadate glasses is studied by x-ray and neutron diffraction experiments. A decrease of the total V-O coordination number from 4·3±0·2 (10 mol% SrO) to 4·0±0·2 (50 mol% SrO) is observed which is interpreted as a transition from networks formed of VO5 and VO4 units to structures formed of only VO4 tetrahedra. The total V-O coordination number seems to be constant up to 30 mol% SrO and it decreases beyond this stoichiometry. The V-O distance peak is highly asymmetric and needs approximation by two or three Gaussian functions. The total Sr-O coordination number is about 8 also with asymmetric Sr-O distance peaks composed by two Gaussian functions. The V-V distances decrease from 0·344 nm (10 mol% SrO) to 0·337 nm in Sr vanadate glasses of 50 mol% SrO. [ABSTRACT FROM AUTHOR]

Neutron diffraction with H/D isotopic substitution is used to investigate the structure of low density amorphous ice produced from (1) high density amorphous ice by isobaric warming and (2) very high density amorphous ice by isothermal decompression. Differences are found in the scattering patterns of the two low density amorphous ices that correlate with structural perturbations on intermediate length scales in the hydrogen bonded water network. Atomistic modeling suggests that the structural states of the two samples may relate to a competition between short range and intermediate range order and disorder. This structural difference in two low density amorphous (LDA) ices is also evident when comparing their compression behavior. In terms of the energy landscape formalism this finding implies that we have produced and characterized the structural difference of two different basins within the LDA-megabasin corresponding to identical macroscopic densities. [ABSTRACT FROM AUTHOR]

Hydrogen/deuterium isotopic substitution neutron diffraction techniques have been used to measure the solute-solute, solute-solvent and solvent-solvent structural correlation functions in a 0.06 mole fraction solution of tertiary butanol in water. The measurements were made at two temperatures, 25 °C and 65 °C. Data analysis to the level of intermolecular orientational correlation functions was performed by the Empirical Potential Structure Refinement (EPSR) technique in combination with a spherical harmonic coefficient analysis. The results reveal in particular a subtle temperature dependence of the intermolecular structure of the solvent water. This structural perturbation is suggestive of a hydrophobic hydration induced, local density enhancement in the solvent water that could relate to the entropic driving force underlying the hydrophobic interaction mechanism. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The phase behavior of sorbed CO2 in an ordered mesoporous silica sample (SBA-15) was studied by neutron diffraction. Surprisingly, upon cooling our sample below the bulk critical point, confined CO2 molecules neither freeze nor remain liquid as expected, but escape from the pores. The phenomenon has additionally been confirmed gravimetrically. The process is reversible and during heating CO2 refills the pores, albeit with hysteresis. This depletion was for the first time observed in an ordered mesoporous molecular sieve and provides new insight on the phase behavior of nanoconfined fluids. [ABSTRACT FROM AUTHOR]