Chemical Disorder Effect On Orthorhombic-Rhombohedral Structural Transition In La0.7ca0.3mno3

High temperature X-ray powder diffraction technique was employed to study the orthorhombic to rhombohedral (O-R) structural transition (ST) in single crystal and ceramics of La0.7Ca0.3MnO3. The data obtained evidence that such ST in both samples occurs in the vicinity of temperature T similar to 700K and demonstrates O and R phases coexistence within the T-intervals of about 20K in crystal and similar to 60K in ceramics. This first order transition is hysteretic on heating and cooling procedures and it is shifted on Delta T similar to 10K to higher temperatures in crystal as compared to the ceramics of the same composition. We have described these features in the terms of the difference between "technologically driven" chemical disorder characteristic for considered samples. Thus, it seems that spatial (up to the micron size scale) fluctuations of the Ca-dopant content in crystal and "mesoscopic scale disorder" within grain boundary regions in ceramics are responsible for both: above noted difference of ST parameters and reported earlier difference in magnetic ordering of these samples. (C) 2013 AIP Publishing LLC.