Two-component systems of isomorphous orientationally disordered crystals. Part 1 Packing of the mixed crystals

Abstract

Five experimental two-component phase diagrams between orientationally disordered crystals (ODICs) have been established from the low-temperature phase to the liquid state using thermal analysis and X-ray powder diffraction techniques. The high-temperature orientationally disordered phases for the pure components, which belong to the series (CH ₃ ) _4–n1 C(CH ₂ OH) _n1 (n ₁ =1,2,3) and (NO ₂ )(CH ₃ ) _3–n2 C(CH ₂ OH) _n2 (n ₂ =0,1) are all face centered cubic. Continuous disordered mixed crystals in the whole range of concentration have been found, which indicates the existence of an isomorphism relationship. The intermolecular interactions in the ODIC state of these systems and other related two-component systems are discussed using the evolution of the packing coefficient as a function of the composition.