orientational glass

In solid-state physics, an orientational glass{{cite journal | last=Loidl | first=A. | title=Orientational Glasses | journal=Annual Review of Physical Chemistry | publisher=Annual Reviews | volume=40 | issue=1 | year=1989 | issn=0066-426X | doi=10.1146/annurev.pc.40.100189.000333 | pages=29–60| bibcode=1989ARPC...40...29L }} is a molecular solid in which crystalline long-range order coexists with quenched disorder in some rotational degree of freedom.

An orientational glass is either obtained by quenching a plastic crystal, (e.g. cyclohexane, levoglucosan{{cite journal | last1=Moura Ramos | first1=Joaquim J. | last2=Diogo | first2=Hermínio P. | title=Orientational glass, orientationally disordered crystal and crystalline polymorphism: A further study on the thermal behavior and molecular mobility in levoglucosan | journal=Journal of Molecular Liquids | publisher=Elsevier BV | volume=286 | year=2019 | issn=0167-7322 | doi=10.1016/j.molliq.2019.110914 | page=110914| s2cid=164662415 }}), or it is a mixed crystal in which positional disorder causes additional disorder of molecular orientations, e.g. CN orientations in KCN:KBr.{{cite journal | last=Knorr | first=K | title=The Glasslike State of the Mixed Alkali Halide-Alkali Cyanides | journal=Physica Scripta | publisher=IOP Publishing | volume=T19B | date=1987-01-01 | issn=0031-8949 | doi=10.1088/0031-8949/1987/t19b/034 | pages=531–536| bibcode=1987PhST...19..531K }}