Short Range Order in Liquid Lithium-Sodium Alloys

Abstract

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

Longitudinal collective modes in simple liquid binary alloys: A computer simulation study

“…11͒ nor the tendency to phase separation of Li-Na. 12 In particular, we have simulated the Li 0.7 Mg 0.3 alloy. To our knowledge there is no experimental information or MD results on the dynamic collective properties of this alloy.…”

Ordering potential in liquid Al–Ge alloys structure and thermodynamics

“…When the alloy presents a phase separation like Li-Na [17], then S CC (0) ! 1 on the miscibility gap.…”

Structure of Cd-Ga Melts Part 2: X-Ray Small-Angle Scattering

“…For molten Li-Na with a nearly critical concentration, aScc(O) «^32 was determined in [5] for a reduced temperature e«t;1.2 10~2. This value is comparable to Scc (0)^23.6, which was obtained from Fig.…”

“…Nevertheless, a comparison of the present exponents with the few data reported for metallic systems is of interest. For Bi-Ga, the classical exponents v = 0.5 and y -1.0 were reported [4], By means of neutron scattering, for Li-Na melts in [5], values of y = 0.57 and y -1.1 were evaluated for 1.2-10 -2 e ^ 1.7 • 10" 1 , whereas for 10~4 ^ e ^ 1.5 • 10~2 with the same system by means of X-ray scattering, v = 0.655 ± 0.03 and y-1.296 ± 0.061 are reported in [9]. Thus, the exponents obtained from Li-Na melts and from Bi-Ga melts are in good agreement with those obtained from Cd-Ga melts.…”

“…In binary melts with segregation tendency, the Until now, small-angle scattering has only been observed in melts of the following binary metallic systems: Ag-Ge [1], Au-Cs [2], Bi-Cu [3], Bi-Ga [4], Bi-Zn [4], Ga-Pb [4], and Li-Na [5] by neutron scattering and Al-In [6], Al-Sn [7], Cs-Na [8], and Li-Na [9] by X-ray scattering.…”