The structural and mechanical properties of Gd and Nd substituted double layered LaCaMnO7 ceramics

We report the results of a detailed study for the structural, microstructural and mechanical properties of Gd and Nd substituted LaCaMnO₇ samples by using XRD, SEM, EDX and dynamic Vickers micro-hardness measurements. The lattice parameters, impurity phases and crystallite sizes are determined from the XRD analysis while the surface morphology and microstructure examinations are carried out from the SEM analysis. While XRD results indicate that neither Gd- nor Nd-substitution changes the lattice parameters significantly, SEM micrographs display quite different average grain sizes of 1.40 and 0.84 μm for Gd- and Nd-substituted samples, respectively. From the Vickers micro-hardness measurements, the values of the contact depth and the area of the indent imprint, the creep, the stiffness, the apparent micro-hardness, the reduced elastic modules and the elastic recovery ratios are computed for both samples. It is observed that these mechanical properties depend on the load and the substitutional specie. The indentation induced cracking model is used to analyze the measured hardness and the true micro-hardness values of 2.58 GPa and 2.91 GPa are found for the Gd- and Nd-substituted samples, respectively. The possible mechanism for the observed changes in microstructural and mechanical properties due to Gd and Nd substitution with La are, also, discussed.