Thermogravimetric analysis showed a very low level of oxygen deficiency (delta) in CaFe2O4-delta, varying in the range 0.003-0.006 at oxygen partial pressures from 10(-5) to 0.2I arm and 295-1223 K, in agreement with Mossbauer spectroscopy. This results in substantial dimensional stability on reducing p(O-2) as revealed by the controlled-atmosphere dilatometry, but also in low concentrations of the ionic and electronic charge carriers. The steady-state oxygen permeability of dense CaFe2O4-delta ceramics is determined by both bulk ionic conduction and surface exchange kinetics. The oxygen-ion transference numbers calculated from the faradaic efficiency and permeation data, are (0.2-7.2) x 10(-4) at 1123-1273 K, increasing with temperature. The atomistic computer simulations indicate a significant energetic affinity for the defect cluster formation involving oxygen vacancies and Fe2+ cations, and unfavorable vacancy location in the oxygen sites forming one-dimensional pathways with minimum migration energy. As a consequence, the partial oxygen-ionic conductivity of CaFe2O4-delta is as low as 3-210 mu S/cm at 1123-1273 K in air. The average thermal expansion coefficients of calcium ferrite ceramics lie in the range (12.0-13.9) X 10(-6) K-1. (c) 2007 Elsevier B.V. All rights reserved.