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

Abstract

X-ray small-angle scattering experiments were performed on nine melts of the Cd-Ga system at different temperatures up to 440°C. Evaluation of the data follows the Ornstein-Zernike theory of critical scattering, thus yielding correlation lengths £ of concentration fluctuations and the long-wavelength limit Sec (0) of the Bhatia-Thornton structure factor. Studies of the concentration and temperature dependence of £ and Sec (0) indicate that the critical point occurs at cc = 50.0 ± 1-0 at % Ga and Tc -295.2 ± 0-1° C. For a melt with the critical concentration, Sec (0) increases up to 3500 times the ideal $cc (0)=CACB-This indicates a strong segregation tendency. In the vicinity of the critical point of the Cd-Ga system, experimental correlation lengths | > 100 A were obtained. The critical-point exponents v and y were determined. It follows that the behaviour of a critical Cd-Ga melt satisfies the prediction of the classical mean-field theory for higher temperatures, whereas, within experimental accuracy, the lattice-gas predictions are satisfied upon approaching the critical temperature.

Anomalous behaviours of the electrical resistivity of the melt of a typical III-V Ga-Sb system

“…In [11], dρ/dT seems to be more sensitive to concentration fluctuations than ρ itself. The existences of such anomalies derived from concentration fluctuations have been revealed for liquid alloys with critical mixing by means of measurements of the heat capacity [13,14], ultrasonic absorption [15], viscosity [16], thermoelectric power [17], and small-angle scattering of neutrons or x-rays [18][19][20][21][22]. Recently, experimental studies of ρ for some liquid alloys with two-liquid-phase separation were performed in detail both under gravity and under microgravity, and the temperature coefficient, dρ/dT , is found to be a good indicator of concentration fluctuations in the homogeneous liquid phase [23,24].…”

The critical behaviour under microgravity of liquid alloys with mutual immiscibility

“…Bi-Ga NS [9] 69 at% Ga ASV [24] 67 at% Ga Present (ER) 70 at% Ga 534.9 ± 0.1 0.348 ± 0.03 1.9 × 10 −4 -7.5 × −2 Cd-Ga XS [11] 50…”

“…The critical behaviour of liquid alloys with immiscibility has been studied by small angle neutron scattering (SANS) for liquid Li-Na [5][6][7], liquid Bi-Ga [8], liquid Bi-Zn and Pb-Ga [8,9] and small angle x-ray scattering (SAXS) for liquid Cd-Ga [10,11]. The temperature dependence of liquid structures at the critical composition, X c , has been summarized by the following power law formulae:…”