Negative Thermal Expansion of ZrW2O8 and HfW2O8: Contradiction to a   Thermodynamic Relation
  It has been shown that the dependence of negative thermal expansion coefficient of ZrW2O8 and HfW2O8 on the temperature found by many authors contradicts to an important thermodynamic relation. 
I. A. Stepanov (University of Freiburg, Freiburg, Germany)