EFFECTS OF PRESSURE AND OF THERMAL HISTORY ON THE STRUCTURAL PHASE-TRANSITION OF KCN

The cubic-noncubic structural phase transition of a KCN single crystal is studied as a function of thermal history and of hydrostatic pressure up to 2 kbar. The standard sequence of phases is cubic-monoclinic-orthorhombic on cooling and orthorhombic-cubic on heating. The monoclinic phase is also absent in first cooling runs at low pressures (p less-than-or-equal-to 250 bar). The width of the monoclinic field in p, Tphase diagram is increased in second cooling runs. The effects are discussed in terms of a martensitic transformation behaviour and random strain fields.