Calorimetric and x-ray diffraction studies of alpha-to-beta structural phase transitions in HfW2O8 and ZrW2O8 - art. no. 184109

A powder x-ray diffraction experiment was performed on cubic HfW2O8 and ZrW 2O8 from 90 to 560 K. The lattice parameter and absolute negative thermal e xpansion coefficient of HfW2O8 are smaller than those of ZrW2O8. The heat c apacity of HfW2O8 was measured from 340 to 520 K using an adiabatic scannin g calorimeter. An anomaly in heat capacity of HfW2O8 corresponding to the a lpha -to-beta structural phase transition was clearly detected around 463 K . The phase transition temperature of HfW2O8 by the calorimeter is 26 K hig her than that of ZrW2O8. The entropy of transition of HfW2O8 is the same ma gnitude as that of ZrW2O8, indicating that the mechanism of the phase trans ition of HfW2O8 and ZrW2O8 is the same.