Résumé
The present paper reports on the synthesis, structure and electrical properties of the La1.85Ca0.15CuO3.5 compound. The topotactic reduction of the tetragonal oxide T-La1.85Ca0.15CuO4-delta with CaH2 results in the formation of La1.85Ca0.15CuO3.5. The powder X-ray diffraction data have shown that La1.85Ca0.15CuO3.5 adopts a face-centered monoclinic crystal structure (A 2/m, a = 8.6224(6), b = 3.8446(2) angstrom, c = 13.0179(10) and beta = 109.690(5)degrees) with anion vacancies located within the CuO2 (CuO1.5 square(0.5), where square represents an anion vacancy) layer of the phase. The topotactic reduction of the complex transition metal La1.85Ca0.15CuO4-delta may lead to the preparation of novel anion-deficient phases with unique transition metal-oxygen sublattices which cannot be prepared via the reduction of all-oxide substrates. The structural and chemical selectivity of the reduction process by anion de-intercalation and oxidation by anion insertion are reviewed. The oxidative monoclinic (La1.85Ca0.15CuO3.5) to tetragonal (T'-La1.85Ca0.15CuO4-delta) transition occurs at 380 degrees C. The structural determination combined with accurate compositional and electrical characterization indicates a change in the charge-compensating mechanism with phase transition. (C) 2016 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University.