Hydration and Proton Transport in BaCaхLa1 − хInO4 − 0.5х (х = 0.1 and 0.2) Phases with Layered Structure

Resumo

Phases of BaCa_0.2La_0.8InO_3.9 and BaCa_0.2La_0.8InO_3.9 compositions are obtained for the first time by means of solid-phase synthesis based on compound BaLaInO₄ with a block (layered) structure from the Ruddlesden–Popper series. According to results from thermogravimetry, these phases (orthorhombic syngony) are capable of reversible (according to XRD data) dissociative absorption of water from the gas phase with the formation of phases of the BaCa_0.1La_0.9InO_3.95 · 0.66Н₂О and BaCa_0.2La_0.8InO_3.9 · 0.92Н₂О compositions (monoclinic syngony). The resulting energetically nonequivalent OH^– groups are characterized by different thermal stability, so the release of H₂O occurs in multiple steps starting at 250°C and is complete above 800°C. Electrical conductivity measurements at 400–900°С show an increase in total conductivity (σ ≈ 10⁻⁴ S/cm at 600°C) by about 1.5 orders of magnitude, relative to the undoped BaLaInO₄ phase. An increase in humidity raises the conductivity by up to 2 orders of magnitude as a result of the transfer of protons (σ ≈ 10⁻⁴ S/cm at 500°C). Transport numbers measured by means of EMF confirm proton transfer and its dominance below 500°C when t(H) ≈ 0.8.