Abstract
Transitions into the magnetically ordered state in function of the average A-cation radius, 〈 r A〉, have been studied by neutron powder diffraction for (La 1− y Pr y ) 0.7Ca 0.3MnO 3 perovskites (LPCM- y×100) with various oxygen isotopes [natural, p( 16O)∼99.7%, and substituted, p( 18O)∼75%]. Comparing both series of samples, qualitatively the same type of phase diagrams (PD) are found for Pr concentrations in the range 0.25⩽ y⩽1.0. This includes the homogeneous regions for small (FM metallic) and large (AFM insulating) y values and the phase-separated state between them. The most important difference is the shift in the PD of the 18O-samples towards the higher 〈 r A〉 (smaller y) border. This means that isotope substitution in LPCM causes a strong redistribution of the energy balance between the charge-ordered insulating and ferromagnetic metallic states.
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