Standard values of Gibbs free energy, entropy, and enthalpy of Na2Ti6O13 and Na2Ti3O7 were determined by evaluating emf-measurements of thermodynamically defined solid state electrochemical cells based on a Na-beta"-alumina electrolyte. The central part of the anodic half cell consisted of Na2CO3, while two appropriate coexisting phases of the ternary system Na-Ti-O are used as cathodic materials. The cell was placed in an atmosphere containing CO2 and O-2. By combining the results of emf-measurements in the temperature range of 573 less than or equal to T/K less than or equal to 1023 and of adiabatic calorimetric measurements of the heat capacities in the low-temperature region 15 less than or equal to T/K less than or equal to 300, the thermodynamic data were determined for a wide temperature range of 15 less than or equal to T/K less than or equal to 1100. The standard molar enthalpy of formation and standard molar entropy at T = 298.15 K as determined by emf-measurements are Delta(f)H(m)(0) (-6277.9 +/- 6.5) kJ (.) mol(-1) and S-m(0) = (404.6 +/- 5.3) J (.) mol(-1 .) K-1 for Na2Ti6O13 and Delta(f)H(m)(0) = (-3459.2 +/- 3.8) kJ mol(-1) and S-m(0) = (227.8 +/- 3.7) J (.) mol(-1) K-1 for Na2Ti3O7. The standard molar entropy at T = 298.15 K obtained from low-temperature calorimetry is S-m(0) = 399.7 J . mol(-1) (.) K-1 and S-m(0) = 229.4 J (.) mol(-1) (.) K-1 for Na2Ti6O13 and Na2Ti3O7, respectively. The phase widths with respect to Na2O content were studied by using a Na2O-titration technique. (C) 2003 Elsevier Ltd. All rights reserved.