Anomalous lattice heat capacity of orientationally glassy crystal of p-chloronitrobenzene at low temperatures

Heat capacities of the ordered and disordered crystalline p-chloronitrobenzene, of which the latter is in glassy state below 245 K, were measured down to 0.3 K. The heat capacity of the disordered state exceeds five times that of the ordered phase at 1 K. The temperature dependence of the heat capacity of the disordered state is weaker than that expected by the Debye model. No hump in Cp/T3 was observed for the disordered phase. The behavior is discussed in relation to low-energy excitation in amorphous materials.