Electrical conductivity relaxation experiments were performed on thin specimens of (x = 0.1, 0.4) at oxygen partial pressures in the temperature range 923 to 1223 K. The transient response of the electrical conductivity after a sudden change of the ambient oxygen partial pressure was analyzed in the frequency domain. The latter procedure allowed diffusion‐limited and surface exchange‐limited kinetics of re‐equilibration to be distinguished. The response of specimens with thicknesses of 350 to 460 μm indicated diffusion‐controlled kinetics at . The chemical diffusion coefficients, D̃, were found invariant with oxygen pressure. At 1073 K the absolute values were for x = 0.1 and for x = 0.4, with activation energies of about 80 kJ/mol. The equilibration process was governed by surface exchange at . The surface exchange coefficient, k _O, was proportional to , where n = 0.65 to 0.85. This pressure dependency was interpreted in terms of a slow surface process involving an oxygen molecule and a surface oxygen vacancy, and causes the observed sharp transition from diffusion‐ to exchange‐controlled kinetics. The activation energy of k _O was estimated at 110 to 135 kJ/mol.

A highly hydrothermally stable microporous network material has been developed that can be applied in energy-efficient molecular sieving. The material was synthesized by employing organically bridged monomers in acid-catalysed sol–gel hydrolysis and condensation, and is composed of covalently bonded organic and inorganic moieties. Due to its hybrid nature, it withstands higher temperatures than organic polymers and exhibits high solvolytical and acid stability. A thin film membrane that was prepared with the hybrid material was found to be stable in the dehydration of n-butanol at 150 °C for almost two years. This membrane is the first that combines a high resistance against water at elevated temperatures with a high separation factor and permeance. It therefore has high potential for energy-efficient molecular separation under industrial conditions, including the dehydration of organic solvents. The organically bridged monomers induce increased toughness in the thin film layer. This suppresses hydrolysis of Si–O–Si network bonds and results in a high resistance towards stress-induced cracking. The large non-hydrolysable units thus remain well incorporated in the surrounding matrix such that the material combines high (pore) structural and mechanical stability. The sol mean particle size was found to be a viable parameter to tune the thickness of the membrane layer and thus optimize the separation performance. We anticipate that other hybrid organosilicas can be made in a similar fashion, to yield a whole new class of materials with superior molecular sieving properties and high hydrothermal stability.