Estructura cristalina y propiedades eléctricas de las soluciones sólidas Dy_1-xCa_xMnO₃

Abstract

Solid solutions corresponding to the Dy 1-x Ca X MnO 3 system, x=0.0 to 0.60 have been studied. The powders were prepared by solid state reaction of the corresponding oxides and carbonates. Sintered bodies were obtained by firing between 1250 and 1450ºC. All the compositions showed single-phased perovskite-type structure with orthorhombic symmetry and Space Group Pbnm. Increase of the CaO content leads to a monotonic decrease of the orthorhombicity factor b/a with the Ca 2+ concentration up to x=0.60. All the solid solutions crystallised with the same O'-type orthorhombic perovskite structure such as pure DyMnO 3 . Electrical measurements have shown semiconducting behaviour for all the solid solutions. The room temperature conductivity increases monotonically with the CaO content. The 60/40 Ca/Dy composition showed a high value of the electrical conductivity and a correlative very low value of the activation energy. Thermally activated small polaron hopping mechanism controls the conductivity of these perovskite ceramics.Keywords: Perovskites, manganites, Crystalline structure, electrical conductivity. Estructura cristalina y propiedades eléctricas de las soluciones sólidas Dy 1-x Ca x MnO 3Se han estudiado soluciones sólidas correspondientes al sistema Dy 1-x Ca x MnO 3 , x=0.0 a 0.60. Los polvos cerámicos fueron preparados por reacción en estado sólido de los correspondientes óxidos y carbonatos. Los materiales cerámicos se obtuvieron por sinterización entre 1250º y 1450ºC. Todas las composiciones fueron monofásicas y mostraron una estructura tipo perovskita, con simetría ortorrómbica y Grupo Espacial Pbnm. El aumento del contenido en CaO llevó a una disminución monóto-na del factor de ortorrombicidad, b/a. Todas las soluciones sólidas cristalizaron con el mismo tipo de estructura perovskita ortorrómbica O', como la del compuesto puro DyMnO 3 . Las medidas eléctricas mostraron comportamiento semiconductor en todas las soluciones sólidas. La conductividad a temperatura ambiente aumenta monótonamente con el contenido de CaO. La composición 60/40 mostró un elevado valor de conductividad y un correlativo bajo valor de la energía de activación. Un mecanismo de salto térmicamente activado de pequeño polarón controla la conductividad de las perovskitas.

Atomic distribution, local structure and cation size effect in o-R1−xCaxMnO3(R = Dy, Y, and Ho)

“…Although Ca 2+ is larger than all these rare-earth ions under consideration, the lattice shrinks upon the incorporation of dopants, indicating a change in the structural distortion. Our calculated results on the x-dependent lattice variation of o-R 1−x Ca x MnO 3 accord well with experimental data [32][33][34][35], thus further proving the validity of our potentials.…”

“…Therefore, the size effect can be neglected in our simulation. The robustness of the proposed potential sets are further checked through investigation of the Ca doping concentration dependence of the lattice parameters of o-R 1−x Ca x MnO 3 , and the comparison with experimental observations [32][33][34][35] is shown in figure 1. The potential and shell model parameters of CaMnO 3 used in this work are taken from our earlier study [36].…”