Microhardness of flux grown pure doped and mixed rare earth aluminates and orthochromites

Abstract

The results of microhardness measurements on flux-grown crystals of (i) single (pure) rare earth aluminates RAlO3 (R = Eu, Gd, Dy, Er) and rare earth orthochromites RCrO3 (R = Y, Gd, Yb), (ii) rare earth aluminates doped with neodymium, erbium, ytterbium and holmium, and (iii) mixed rare earth aluminate crystals of the type (La1−x) Pr(x)AlO3 (x=0, 0.25, 0.75 and 1.00) are presented. The variations in the microhardness value with load are non-linear in all cases. Kick's law fails to explain the observed variations. Instead, they are best explained by the application of the idea of materials resistance pressure in the modified law proposed by Hays and Kendall. The results indicate that the doping does not increase the hardness value of crystals in all cases. The hardness instead depends on the composition of the parent material as well as the dopant entering into the crystal lattice. Mixed rare earth aluminate crystals are shown to be harder than those of single rare earth aluminates.