Ba-2(In1 - xMx)(2)O5-y/2(OH)(y)square(1) (-) (y/2) (y <= 2; M = Sc3+ 0 <= x < 0.5 and M = Y3+ 0 <= x < 0.35) Compounds were prepared by reacting Ba-2(In1 - xMx)(2)O-5 Phases with water vapor. This reaction is reversible. Analyses of the hydration process by TG and XRD studies show that the thermal stability of hydrated phases increases when x increases and that the incorporation of water is not a single-phase reaction inducing either a crystal system or space group modification. Fully hydrated (y = 2) and dehydrated (y = 0) samples have been stabilized at room temperature and characterized for all compositions. In wet air, all phases show a proton contribution to the total conductivity at temperatures between 350 and 600 (C degrees). At a given temperature, proton conductivity increases with the substitution ratio and reaches at 350 degrees C, 5.4 10(-3) S cm(-1) for Ba-2(In0.65Sc0.35)(2)O-4.2 square(0.2)(OH)(1.6). (C) 2009 Elsevier B.V. All rights reserved.