Room temperature structural and microstructural study for the magneto-conducting La5/8-xPrxCa3/8MnO3 (0≤x≤5/8) series

Las(5/8-x)Pr(x)Ca(3/8)MnO(3) (x = 0, 0.1, 0.2, 0.25, 0.3, 0.35, 0.375, 0.4, 0.412, 0.425, 0.45, 0.5, 5/8) series has been synthesized by the ceramic method. All manganites are single phase crystallizing in the Pnma space group. The evolution of cell parameters along the series indicates that the orthorhombic perovskite superstructure distortion subtype switches from O" (x = 0; c > a > b/root2) to O' (x = 5/8; a > c > b/root2). This change is not abrupt and there is a wide compositional range (0.25 less than or equal to x less than or equal to 0.35) where the distortion subtype cannot be defined. We report high-resolution RT synchrotron and neutron powder diffraction data for four selected compositions (x = 0, 0.2, 0.35, and 5/8). Atomic parameters determined from the joint Rietveld refinement indicate that the tilting scheme slightly changes along the series. The tilting angle of the MnO6 octahedra around the b long-axis is larger than that around [101] for the O" subtype but is smaller than that for the O' subtype. For the x = 0.35 sample, where phase separation has been observed at low temperatures, the average tilting angles are the same within the small errors of the measurements. The microstructures of the samples have been investigated through Williamson-Hall plots for the synchrotron patterns. The sample broadening is markedly anisotropic and strongly dominated by microstrains with average values of the Deltad/d term of about 10 x 10(-4). The sample broadening for Pr5/8Ca3/8MnO3 is larger than that for La5/8Ca3/8MnO3 although the Pr3+ radius is more similar to that of Ca2+. This indicates that other factors, in addition to A-cation radii mismatch and variance, such as distortion type, are important to justify the broadening commonly observed in manganites. The monotonic evolution in cell parameters, the magnetization, and resistivity curves indicate the good quality of the samples.