Enthalpy of formation of Ba₃SrNb₂O₉

Ba₃SrNb₂O₉ is a quaternary fission product oxide. It is also a technologically important compound due to its excellent intrinsic properties, such as ferroelectric-piezoelectricity, electro-optics properties etc. Thermodynamics plays an important role in predicting long term stability of these materials under different reactive conditions. The present paper describes determination of molar enthalpy of formation of Ba₃SrNb₂O₉ (s) compound employing a high temperature solution calorimeter. The reaction enthalpies of MCO₃ (where M= Ba/Sr), Nb₂O₅(s) and Ba₃SrNb₂O₉ (s) in liquid PbO + B₂O₃ solvent (2:1 molar ratios) at 966K were measured. The value of Δ_fH°₂₉₈ of Ba₃SrNb₂O₉(s) at 298K was found to be -622±5 kJ mol^-1. (author)