INFLUENCE OF ROTATIONAL MOTION OF NITROGEN MOLECULES ON THE THERMAL-EXPANSION OF SOLID-SOLUTIONS OF AR-N-2 - A NEW EFFECT

The thermal expansion coefficient of solid Ar and of solid solutions o f N-14(2) in Ar (0.51; 2.24; 4.89 mol.% N-14(2)) has been investigated in the temperature range 1-16 K. Two new effects have been discovered for the behaviour of the impurity contribution Delta alpha to the lin ear expansion coefficient, i.e., negative values of Delta alpha at T < 4.3 K for the solution with a nitrogen concentration of 0.51%, and in dependence of Delta alpha on impurity content for two more concentrate d solutions below 7 K. An explanation of the peculiarities mentioned i s given. The comparison of the results obtained with the theoretical p redictions has been made.