Evolution of (La1-yPry)(0.7)Ca0.3MnO3 crystal structure with A-cation size, temperature, and oxygen isotope substitution

The atomic structure of (La1-yPry)(0.7)Ca0.3MnO3 compound with 0.5 less tha n or equal to y less than or equal to 1 has been systematically studied by neutron powder diffraction in the temperature range from 15 to 293 K. For c omposition with y = 0.75, the structural analysis was performed on two samp les, one containing the natural mixture of oxygen isotopes and the other on e 75% enriched by O-18. The room temperature structural characteristics of the series, including cell volume, average Mn-O bond distance, and average Mn-O-Mn bond angle, are the linear functions of the [r(A)] Temperature depe ndencies of these parameters are quite smooth, except for the point T = T-F M, where a jump like changes occur. The isotope enriched samples have been found identical in crystal and magnetic structure down to the temperature o f transition of the sample with O-16 into the metallic ferromagnetic phase. It confirms that different transport and magnetic properties of the sample s with O-16 and O-18 at low temperature are driven by the different oxygen atoms dynamics solely. Temperature dependencies of the CO and AFM diffracti on peak intensities and of the peak widths for compositions close to the me tal-insulator boundary (y approximate to 0.75) indicate the macroscopically phase separated AFM-dielectric + PM-metallic state below T-FM.