Abstract
By using neutron diffraction for the identification of phases, the temperature-pressure diagram was determined for solid 4,4'di-n-butyloxyazoxybenzene (4-OAOB), in the temperature range from room temperature to ca. + 115°C and the pressure range from atmospheric pressure to ca. 2 kbar. The possibility of a critical point terminating the coexistence curve of phases I and II is suggested. Undercooling phenomena, and spontaneous transitions from metastable to stable phases are observed and discussed.