X-RAY-DIFFRACTION STUDY OF THE CRYSTAL-STRUCTURES AND ORIENTATIONAL GLASS STATE OF AR1-X(N2)X SOLID-SOLUTIONS

Solid solutions of Ar1-x(N2)x have been investigated by x-ray powder diffraction in the range 0.5<x<1.0, 8<T<60 K, and under hydrostatic pressures up to 2200 bars. The structural hcp-cubic (Pa3) phase transition is identified as a martensitic transformation with a wide transformation hysteresis. For x<0.8 and T<30 K the solid solutions show the orientational glass state, which is characterized by a superposition of inhomogeneous and homogeneous lattice strains. The inhomogeneous component is described by the random-field model. The homogeneous component corresponds to an orthorhombic distortion of the hcp lattice. Two products of the Pa3 phase have been detected: an orientationally disordered fcc state and the high-pressure modification. It is concluded that the Pa3 phase and its products have no direct relevance to the orientational glass state. The analogies to the glasslike state of the mixed cyanides and of ortho-para-H2 are worked out. © 1990 The American Physical Society.