BaTi0.5SC0.5O3 - delta was prepared via solid state reaction route and final sintering at 1550 degrees C. High resolution X-ray powder diffraction on the as-prepared material reveals a cubic perovskite structure with a unit cell parameter, a = 4.1343(1) angstrom. Thermogravimetric analysis revealed the presence of significant levels of protons in the as-prepared material and 74% of the theoretically achievable protonation through filling of oxide ion vacancies was attained on exposure to a humid environment at 185 degrees C. Infrared spectroscopy revealed a broad O-H stretching band confirming the presence of OHo center dot defects. Electrical conductivity was measured with variable frequency AC impedance methods in oxygen, argon, and hydrogen under dry, hydrated (H2O) and heavy water (D2O) conditions. In the temperature range of 150-550 degrees C in a wet gas atmosphere the conductivity is significantly higher than that observed for dry conditions, indicating that protons are the dominant charge carriers. Conductivity is also found to be higher in dry oxygen in comparison with dry argon over the whole temperature range of 150-1000 degrees C, characteristic of contribution from p-type charge carriers under oxidising atmospheres. At 550 C the proton conductivity was estimated to be 2.89 x 10(-4) S cm(-1) in wet Ar. Fitting of conductivity data provides a hydration enthalpy change (Delta H-hydr(0)) of -100 +/- 5 kJ/mol and hydration entropy change (Delta S-hydr(0)) of -160 +/- 10 J/mol K. (C) 2013 Elsevier B.V. All rights reserved.