Heat capacity and order-disorder phase transition in negative thermal expansion compound ZrW2O8

Abstract

Heat capacity of ZrW2O8 was measured in the (1.8 to 483) K temperature range by using two adiabatic and a commercial relaxation calorimeters. Standard thermodynamic functions of ZrW2O8 were estimated from the measured molar heat capacity. A large λ-type anomaly of heat capacity due to an order-disorder phase transition was observed at T = (440 ± 0.5) K. The enthalpy and entropy of phase transition were determined to be (1.56 ± 0.01) kJ · mol-1 and (4.09 ± 0.03) J · K-1 · mol-1, respectively. The magnitude of the entropy of transition supports the order-disorder mechanism previously suggested by the present authors. © 2004 Elsevier Ltd. All rights reserved.