The standard Gibbs free energy of formation of NiTiO3 from its component oxides NiO with rock salt structure and TiO2, with rutile structure Delta(f)G((ox))(o) (NiTiO3) has been measured over a wide temperature range (900 to 1700) K employing the solid-state electrochemical cell: Pt vertical bar Ni + NiTiO3 +TiO2 parallel to(Y2O3)ZrO2 parallel to Ni+NiO vertical bar Pt The measured EMF, which is directly related to the Gibbs free energy of formation of NiTiO3 from component oxides, can be represented by two linear segments; E +/- 0.38/(mV) = 63.48 - 0.01264 (T/K), in the range T = (900 to 1565) K, and E +/- 0.35/(mV) = -16.21 - 0.03831 (T/K), in the range T = (1565 to 1700) K. The change in slope at T = 1565 K is related to the transition from ordered ilmenite structure of NiTiO3 with space group R (3) over bar to a kind of disordered corundum structure with space group R (3) over barc, involving essentially an order-disorder transition on the cationic sublattice. The new measurements help to resolve discrepancies in thermodynamic data on NiTiO3 reported in the literature. (c) 2006 Elsevier Ltd. All rights reserved.