LOW-TEMPERATURE HEAT-CAPACITIES OF ORTHORHOMBIC AND CUBIC PBF2

Heat capacities of orthorhombic (±) and cubic (2) lead fluoride (PbF2) have been measured between 3 and 22 K. For both structures the data can be well fitted to the sum of a Debye term and an Einstein term with exponential temperature dependence. The latter may be attributed to the existence of low-lying vibrational modes in the paraelectric compound. The observed Einstein frequency of 35 cm-1 for the orthorhombic structure agrees with that of a Raman-active mode in PbCl2 and PbBr2 of the same structure, which involves the movement of Pb atoms only. © 1979 The American Physical Society.