Pressure effects on the dynamics of a plastic crystal, adamantane

Adamantane was one of the first "plastic" (orientationally disordered) molecular crystals to have its structure studied by QENS in the 1970s and 80s. Recently, such materials have attracted renewed interest because the large entropy change across their order-disorder phase transitions can be exploited in environmentally friendly barocaloric refrigeration. However, the experimental capability to measure a good QENS signal under pressure has only recently been developed. We recently used a new TaV pressure cell on OSIRIS to study a molecular-ionic barocaloric, ammonium sulfate (AS), and here propose to study dynamic disorder in the molecular system adamantane under pressure in the same way. Our results will be the first reported studies of a well known material under pressure, and in comparison with AS will provide two model systems that differ in important physical respects.