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 of 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 linear 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 independence of Delta alpha on impurity content for two more concentrated solutions below 7 K. An explanation of the peculiarities mentioned is given. The comparison of the results obtained with the theoretical predictions has been made.