H. RUPPERSBERG et al. : Non-Linear Surface-Stress Fields o,,(z) and uyy(z) 68 1 phys. stat. sol. (a) 116, 681 (1989) Subject classification: 62.20 and 68.25; S1.2 For single-phase polycrystalline materials the relation is discussed between the elastic strain ~( y , p) obtained from X-ray diffract'ion experiments and the polynomial expansion of the stress components oJo) and O~+ Q O ( Z ) with respect to the distance z from the external surface of the specimen. -1 universal plot is proposed for F(y, to, (hkl)) = +(c(p) + ~( p + 90)) curves measured for different penetration depths t o of the radiation and for different reflecting lattice planes. This expression also allows absolute scaling of the E values. The formalism is applied for discussing s(y, p, to, (hkl)) curves obtained with synchrotron radiation from a cold-rolled nickel plate. They indicate strongly non-linear variations of stress in a surface layer about two pm thick. F u r einphasige vielkristalline Werkstoffe wird der Zusammenhang zwischen rontgenographisch ermittelten Dehnungen ~( y , p) und den nach dem Xbstand z von der Grenzflache in Reihe entwikkelten Spannungskomponenten oB(z) und O~+ Q O ( Z ) erortert. Es wird eine universelle Auftragung fur E(y, to, (hkl)) = -;-(e(p) + ~( p + 90))-Kurven vorgeschlagen, die fur beliebige Eindringtiefen t o und reflektierende Netzebenen ermittelt werden. Es ergibt sich daraus auch die Moglichkeit, E absolut zu bestimmen. Der Formalismus wird auf c ( y , p, to, (hk2))-Kurven angewendet, die mittels Synchrotronstrahlung fur ein kaltgewalztes Pu'ickelblech erhalten wurden. Es ergeben sich stark nichtlineare Spannungsanderungen in einer etwa 2 pm dicker, Oberflachenschicht.

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The aim of the present paper is to state differences in the spatial distribution of valency electrons for free metal atoms and for molten metals. The element lithium was chosen since both its inner and outer electrons play an important role, so that when a precise X-ray and a precise neutron-diffraction experiment have been carried out a difference, if it exists at all. should be recognizable. The correction of the X-ray data for inelastic, i.e. Compton scattering was done on the basis of an inelastic measurement performed on a spectrometer equipped with a position sensitive detector. The structure factors S (q) calculated from the X-ray and neutron diffraction data show very good coincidence within the whole q-range. Slight deviations for 0 ≦ q ≦ 1.7 Å-1 are discussed but yield no hint at all on electron correlations independent of the nuclei.

The neutron diffraction patterns of liquid lithium lead alloys containing 0, 17, 34, 48, 61, 80, and 100 at.% 7Li were measured. The long-wavelength limit of the partial structure factors aij(k) and of the concentration–concentration correlation function SCC(k) is calculated. These values agree well with the values calculated from activity data. For the 80 at.% alloy the total SCC(k) function was measured. It shows a pronounced first peak at the k value of a prepeak observed with x rays. The Fourier tranform of SCC(k) is related to the short-range order-size coefficients which have been introduced by Warren et al. (Ref. 19) to describe the local order of solid solutions. The data for the liquid Li–Pb alloys indicate a preference for unlike nearest neighbors and a reduction of the distance between unlike nearest neighbors as compared with the mean distance of the pure components. This short-range order is probably due to a partially saltlike bonding between lithium and lead ions. The over-all structure of the liquid alloys is similar to the structure of a hard sphere system.

The density and the velocity of sound of liquid Li-Pb alloys have been measured in the composition ranges 0 -17, 30 -100 at % Pb and 0-10, 40 -100 at % Pb, respectively. The temperature dependence of these properties has been determined for each sample in a temperature range of at least 130 K. The excess volume is negative and has a minimum at about 20at%Pb, where the volume per atom at 800 °C is about 19% smaller than the volume of an ideal solution. The absolute value of the excess volume rises with the temperature, as does the absolute value of the deviation of the adiabatic compressibility from the mean compressibility.

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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

X2b2SNN(q) oscillates around 1. It is equal to S(q) for bl = b2. Its Fourier Transform (FT) is related to the global structure of the alloy 191. S (q) oscil-NC lates around 0. It is identical to zero for identical global surroundings of the 1 and 2 particles.Article published online by EDP Sciences and available at http://dx.