The data for binary and ternary systems Cs-Na, K-Na, Cs-K, Cs-K-Na, Ba-Cs, Be-Ba, Be-Sr, Be-Ca, Be-Mg, Ca-Sr, Ca-Ba. Sr-Ba, Mg-Ba, Mg-Ca and so Cs-F and Lili (lithium hydride) were obtained with the above parameters [8,9,11], The functions for binary alkali-metal systems from liquidus line up to 1200K are demonstrated on Figure l(a,b,c) Discussion Model theories were used for the interpretation of the experimental data and were the basis of their adequate approximation. For the enthalpy of formation ,a quasichemical model was proposed by Guggenheim[10], Developed for these liquid-metal alloys [11] it takes into account the alteration of short-range order structure compared to the random distribution, as well as the concentration and temperature dependencies of the energies of all kinds of pair-wise inter-particle interactions (e.g. three kinds for binary systems). For the entropy of formation (obtained from the difference between experimental values of the enthalpy of formation and the Gibbs energy of formation) the hard-sphere model with a little dependence of hard-sphere diameters on concentration [12 ] as fitting parameter of theory can be used. The long-wave limit of the concentration correlation function was computed for the range of temperatures and concentrations with help of obtained thermodynamic data (for binary systems of alkali metals up to 1200K see Figure 2). These results were compared with available data from the literature (T=400 K) for diffraction experiments (Scc(0) is obtained via the static structure factor S(0)) [14,15 ], as well for some thermodynamic experiments [1-6] and calculations [4,12], There was agreement concerning the magnitude and coordinate of the maximum of the function: It corroborates the existence of long-range fluctuations of concentration in some liquid-metal systems, i.e. micro-non-homogeneous (cluster) structure of the liquid alloy and therefore the decreasing of thermodynamic stability of the system as a homogeneous liquid phase. This fact correlates with phase diagrams, e.g. for the Cs-Na system liquidus line in the named concentration range is practically horizontal. This means that increasing concentration fluctuations show a tendency for phase stratification [3, 4]. Some peculiarities of behavior of the thermodynamic
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