1,720,992 research outputs found
Rietveld Refinement of the paraelectric and ferroelectric phases of PbFe0.5Nb0.5O3 by neutron and X-ray diffraction
No full textRietveld refinements of the paraelectric and ferroelectric structures of PbFe0.5Ta0.5O3
No full textThe high symmetry parent phase and the two derived low symmetry phases of the complex perovskite PbFe0.5Ta0.5O3 have been refined by the Rietveld method from neutron powder diffraction data. The analysed powders were obtained by grinding single crystals. Owing to the Very small distortions from the cubic structure, the lattice symmetry of the derived phases was determined by means of synchrotron radiation powder diffraction. At 350 K the cubic phase (which is known to be stable for T > 270 K) is characterized by positional disorder or anharmonic thermal motion of lead atoms, as happens in most Pb-based complex perovskites. It was refined in space group Pm (3) over bar m, with strongly anisotropic thermal motion of oxygen atoms. The synchrotron powder diffraction pattern of the intermediate phase (stable for 220 K < T < 270 K), collected at 230 K, agrees with a small tetragonal distortion. Neutron data at 230 K were refined in symmetry P4mm. Only oxygen atoms are significantly displaced from the cubic positions. The analysis of line broadening and splitting in the synchrotron radiation patterns collected at 130 K and 15 K indicate the low temperature symmetry to be monoclinic. Neutron data at 15 K were refined in space group Cm
Charge-Ordering and Magnetic Transitions in Nanocrystalline Half-Doped Rare Earth Manganite Ho0.5Ca0.5MnO3
Full text linkThis work investigates nanostructured Ho0.5Ca0.5MnO3, considered a model system of the Ln0.5Ca0.5MnO3 series of manganites with perovskite structures featuring small lanthanide (Ln) ions half-substituted by Ca ions. Here, we propose a modified hybrid sol–gel–solid-state approach to produce multiple samples with a single batch, obtaining very high crystalline quality and ensuring the same chemical composition, with an average particle size in the range 39–135 nm modulated on-demand by a controlled calcination process. Our findings evidence that, provided the crystalline structure is preserved, the charge-ordering transition can be observed even at the nanoscale. Additionally, this research explores the presence of glassy phenomena, which are commonly seen in this class of materials, to enhance our understanding beyond simplistic qualitative observations. Comprehensive characterization using DC and AC magnetometry, along with relaxation and aging measurements, reveals that the complex dynamics typical of glassy phenomena emerge only at the nanoscale and are not visible in the bulk counterpart. Nevertheless, the analysis confirms that even the sample with the smallest nanoparticles cannot be intrinsically classified as canonical spin glass
- …
