The specific heat studies of (NH3CH3)5Bi2Br11: Evidence for the critical end-point in crystals

The specific heat, C-p, of (NH3CH3)(5)Bi2Br11 was measured by adiabatic calorimetry in the temperature range 30-350 K. The "peculiar" character of C-p(T) anomaly (from residual to giant effect) observed in the region 70-100 K in different measurement runs, was interpreted in terms of the critical end-point existence on the temperature-stress, phase diagram. For the first time, a full set of possible C-p(T) curves predicted by theory was registered for near-critical behaviour and for the crystal with a given stoichiometry.