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The short range order of a liquid lithium sodium alloy with nearly critical composition has been studied by small-angle and high-angle neutron diffraction at 10 and 145 K above the critical temperature. In this temperature range the small-angle scattering yields linear Ornstein-Zernike plots from which formally critical exponents and amplitudes could be determined. The atoms prefer like nearest neighbors and the extent of this preference varies only slowly with temperature. S h o r t R a n g e O r d e r in L iq u id L ith iu m -S o d iu m A llo y s IntroductionBecause of the negative coherent neutron scatter ing amplitude of the Li7 isotope, lithium alloys are ideal candidates for the study of short-range order (SRO) by neutron diffraction. Most nuclides have a positive scattering amplitude, and if one of them is mixed with Li' at the so-called zero alloy composi tion the coherent scattering pattern directly reveals the amplitude of concentration-fluctuation waves. In previous papers 2 the SRO of liquid LiPb and LiAg alloys has been investigated. The general physical and chemical behavior of LiPb and LiAg alloys is typical for system with strong and medium tendency, respectively, towards compound forma tion. For both systems a quite similar preference for unlike nearest neighbors has been observed. From preliminary results 3 we have the impression that the stronger bonding of LiPb in the vicinity of the com position Li4Pb is manifested in a larger range of the SRO.In this paper the SRO and its temperature varia tion of the segregating system LiNa is studied. In segregation systems, long-wavelength fluctuations yield strong scattering effects at small wave vectors, and in addition to the usual high-angle scattering experiments special small-angle scattering investiga tions with another instrument become necessary. Because the angular ranges of the two experiments did not overlap, the small-angle region was extrapo lated by means of an Ornstein-Zernike (OZ) plot, and the gap was closed by a smooth interpolation. = 0.397 and r/Li = 0.404. The results of the calculations depend very strongly on the value of the hard sphere diameter chosen for lithium. The value oLi = 2.43 A together which oNa = 3.26 A gave satisfactory quantitative agreement with experiment. According to Schürmann and Parks 5 the effects of the order parameter fluctua tions on the resistivity itself are surprisingly small, but dR/dT rises if the miscibility loop is approached from higher temperatures, and it has a sharp peak at the critical point. This behavior, which the authors call "paraconductivity", cannot be derived from the long-wavelength fluctuations which are related to the small-angle scattering, and on the basis of the dis cussion by Fisher and Langer 10 it is expected to be due to short-wavelength fluctuations. No direct ex perimental information about the amount and the temperature variation of such fluctuations in liquid Unauthenticated Download Date | 5/12/18 12:38 PM

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Following the procedure suggested by May, Ibel & Haas [J. Appl. Cryst. (1982), 15, 15-19] for the correlation of transmission data with the level of neutrons scattered incoherently into the full solid angle 4n measurements have been made of the transmission and incoherent scattering intensities of aqueous buffers of different HEO/D20 ratios at temperatures between 280 and 343 K. That it is possible to extend the proposed calibration procedure to absorbing-ions-containing buffers is also shown.

Small‐angle neutron scattering experiments have been performed with aqueous dispersions of binary lipid mixtures. One component was protonated, the other was partly deuterated. By varying the mole fraction of the deuterated species the mean scattering‐length density of the lipid lamellas and hence the contrast between liposomes and the solvent was changed. It is shown that this inverse contrast variation has the advantage of (i) a simpler data analysis, (ii) an increased resolution of homogeneous and heterogenous lipid distributions and (iii) a considerably increased sensitivity for the evaluation of phase diagrams in segregated lipid mixtures. Phase boundaries can now be determined to an accuracy of better than 1 mol%.