Vaporization studies over (NiO + Ni2Te3O8) in the Ni-Te-O system were carried out by transpiration thermogravimetry (TTG) and Knudsen effusion mass spectrometry (KEMS) in the temperature ranges of 960-1085 K and 850-960 K, respectively. Comparison of total pressures obtained by TTG with that deduced using partial pressures of vaporizing species from KEMS showed a good agreement providing reliable vapor pressures over this phase region. From vapor pressures, enthalpies of solid-gas and gas-phase equilibria were evaluated. Subsequently, enthalpy and Gibbs free energies of formation of Ni2Te3O8(s) were deduced at 298.15 K: Delta H-f(m)degrees = -1543 +/- 46 kJ mol(-1); Delta(f)G(m)degrees = 1294 +/- 46 kJ mol(-1). A thermochemical assessment was made to examine the possibility of formation of the ternary Ni2Te3O8(s) phase on stainless steel clad of mixed-oxide fuelled fast breeder nuclear reactors. (C) 2014 Elsevier B.V. All rights reserved.