COMPARATIVE-STUDY OF HEAT PROPERTIES OF RARE-EARTH MOLYBDATES

The specific heat of two improper ferroelectric rare earth molybdates Tb-2(MoO4)(3) (TMO) and Gd-2(MoO4)(3) (GMO) was measured in the region 85-560 K by means of ac-and adiabatic calorimetry. Two anomalies were revealed after careful subtraction of the background specific heat fo r both crystals and were attributed to ferroelectric phase transitions (T-0 = 429.8 K and 431.4 K, respectively) and to a possible trace of an isomorphic phase transition (270K and 240K). The critical exponents for To were estimated taking into account the first-order nature of f erroelectric phase transition (alpha'=0.50+/-0.03, alpha=1.35+/-0.15).