Synthesis of Several Tungsten (VI) Complex Perovskites, Ba(B III 2/3 W 1/3 )O 3 (B = In, Y, Dy, Gd, Sm) by the Polymeric
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Synthesis of Several Tungsten (VI) Complex Perovskites, Ba(BIII2/3W1/3)O3 (B = In, Y, Dy, Gd, Sm) by the Polymeric Precursors Method Antonio F. Fuentes, Guillermo Mendoza-Suarez, J. Iván Escalante-García, Ulises Amador1 and Khalid Boulahya2 CINVESTAV-IPN Unidad Saltillo, Apartado Postal 663, 25000 Saltillo, Coahuila, Mexico. 1 Departamento de CC. Químicas, Facultad de Ciencias Experimentales y de la Salud, Universidad San Pablo-CEU, Urbanización Montepríncipe, 28668-Boadilla del Monte, Madrid, Spain. 2 Departamento de Química Inorgánica, Facultad de Ciencias Químicas, Universidad Complutense, 28040-Madrid, Spain ABSTRACT We show in this work the usefulness of the polymeric precursors method to obtain several Ba(BIII2/3W1/3)O3 (B = In, Y, Dy, Gd, Sm) complex perovskites. Solid resins obtained from solution were treated at different temperatures and characterized by XRD and thermal analysis. BaCO3 and Ba(NO3)2 were the only crystalline species found below 500°C. Tungstates with different stoichiometry evolve from the powdered precursors as the temperature is raised. Formation of perovskite-like phases is evident in all five cases, above 1000°C. XRD results suggest also that trivalent ions do not participate in chemical reactions below that temperature since the presence of any binary phase containing them could be confirmed. INTRODUCTION Complex perovskites have attracted the interest of many research groups worldwide in different areas of materials science because of their frequently, unusual physical properties and wide range of applications [1-3]. Since it is the B octahedrally coordinated cation in ABO3 perovskites the one that generally determines their physical properties, complex perovskites where two different ions simultaneously share this B-site, such as A(B’1/2B’’1/2)O3 or A(B’2/3B’’1/3)O3, display a variety of interesting electrical and magnetic properties. Although many papers can be found in literature dealing with A(B’1/2W1/2)O3 complex perovskites, where B’ is a divalent ion [4, 5], not much information is available about similar A(B’2/3W1/3)O3 perovskites [6, 7]. We have recently engaged ourselves in the study of this type of compounds where the combination of W(VI) with trivalent elements such as In, Y or Ln3+ in a perovskite framework, could yield compounds with interesting electrical and optical properties. The processing method selected to prepare the title compounds was the complex polymeric precursors method [8]. This method was selected because starting from solution, it leads to a more homogeneous mixing and higher reactivity of the starting reagents minimizing phase segregation compare to the traditional solid state reaction. EXPERIMENTAL Starting reagents used were: barium carbonate (BaCO3, 99.98%), hydrated metal nitrates (99.9%) and ammonium tungsten oxide [(NH4)10W12O41.5H2O, 99.999%]. Chemical reagents
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were weighed in the appropriate stoichiometric ratio to obtain Ba(BIII2/3W1/3)O3 and dissolved in an aqueous citric acid solution (CA) under constant stirring. After
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