Several PbZr 1−x Ti x O 3 (PZT) compositions in the proximity of the morphotropic phase boundary (MPB) were examined by means of Raman spectroscopy in the 15-800 K temperature range. Previous studies performed by other researchers using various techniques evidenced that, in the phase diagram of PZT, areas with rhombohedral/monoclinic and tetragonal/monoclinic phases coexist across the MPB. For these compositions, either long-range or short-range symmetry ordering of the monoclinic phase should be considered, so that no true rhombohedral-monoclinic-tetragonal phase boundary exists. In addition, the onset of antiferrodistortive phase transitions between high-T and low-T perovskite phases has been predicted by ab initio calculations and experimentally reported. In the present work, low-T and high-T Raman scattering spectra were collected on undoped PbZr 1−x Ti x O 3 with compositions x = 0.42, 0.45, 0.465, 0.48 and 0.53 in an attempt to clarify the current open issues on the phase diagram of PZT. Spectra clearly belonging to the respective phases were observed in the rhombohedral, monoclinic and tetragonal areas, thus confirming that monoclinic ordering is long-range only for a narrow range of compositions. Raman measurements at cryogenic temperatures allowed detecting all predicted low-T phases, including the tetragonal one. These results are in good agreement with both ab initio calculations and experimental results obtained by other authors on the same compositions.

BiFeO 3 is a multiferroic material showing antiferromagnetic ordering and ferroelectric behavior simultaneously. Here, Mn-doped BiFeO 3 nanoparticles were synthesized up to 10% of Mn composition by a sol-gel process. The samples showed high crystallinity with no secondary phase up to 2% of Mn doping. A phonon peak at 1250 cm −1 in undoped BiFeO 3 showed anomalous intensity enhancement in the magnetically ordered phase below T N = 643 K due to a spin-phonon coupling. This behavior was less pronounced in the Mn-doped samples, suggesting a suppression of magnetic ordering between Fe 3+ spins by Mn doping.

Ho(3)Fe(5)O(12) crystallizes in a body-centered cubic lattice and shows no ferroelectricity because of its highly symmetric (centrosymmetric) crystal structure. However, in heteroepitaxially grown thin films, Ho(3)Fe(5)O(12) may exhibit ferroelectricity because of lattice strains induced by the substrate. In this work, heteroepitaxial films of Ho(3)Fe(5)O(12) were grown with different thicknesses of 50-160 nm and studied by x-ray diffraction and Raman scattering. The results were compared with those of bulk polycrystals to characterize residual strains. At room temperature, Raman spectra of films revealed a phonon frequency shift from those of bulk samples, showing lattice distortion. There was a difference in the lattice distortion scheme between the thinner and thicker films. Results of x-ray diffraction were well correlated with the Raman data. Raman measurements at 300-800 K showed the existence of lattice strain up to ∼650 K. This suggests a remanent-polarization character of Ho(3)Fe(5)O(12) films up to this temperature. Closeness between the magnetic ordering temperature T(N) = 567 K and T(C)∼650 K may bring us the ideal multiferroic material with an enhanced magnetoelectric effect at room temperature.