Abstract
A series of (La 1− y Pr y ) 0.7Ca 0.3MnO 3 samples with y=0.5, 0.6, 0.7 and 0.75 has been systematically studied by neutron powder diffraction. The analysis shows that their basic structural parameters including the temperature of metal–insulator-phase transition are the linear functions of an average A-cation radius. For composition with y=0.75 the structural analysis was performed on two samples, one containing the natural mixture of oxygen isotopes (99.7% 16 O , metallic and ferromagnetic at T⩽ T FM≈110 K), and the other one enriched by 18 O in 75% (insulating in the whole temperature range and with collinear antiferromagnetic order at T⩽ T AFM≈150 K). These two samples have been found to be identical in crystal and magnetic structure down to transition of the sample with 16 O into the metallic ferromagnetic phase. This means that their quite different transport and magnetic properties at T⩽110 K are driven solely by the different oxygen atoms dynamics. Evidences of low-temperature two-phase state: AFM-dielectric+FM-metallic have been obtained for the samples with y⩾0.6.
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