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We report a structural evolution analysis of the long-range and local order and disorder of lead scandium niobate (PSN) down to 10 K, using a combination of neutron and x-ray diffraction on powder and single crystals. The structure of PSN is discussed and compared with those of simple perovskite compounds and . In PSN the existence of a long-range but still disordered ferroelectric phase, different from those of simple perovskites, is evidenced. The disorder of lead and scandium/niobium atoms on short-, medium- and long-range scales is discussed in connection with the dielectric properties of these materials.

Low temperature properties of BaZrO3 are revealed by combining experimental techniques (X-ray diffraction, neutron scattering and dielectric measurements) with theoretical first-principles-based methods (total energy and linear response calculations within density functional theory, and effective Hamiltonian approaches incorporating/neglecting zero-point phonon vibrations). Unlike most of the perovskite systems, BaZrO3 does not undergo any (long-range-order) structural phase transition and thus remains cubic and paraelectric down to 2 K, even when neglecting zero-point phonon vibrations. On the other hand, these latter pure quantum effects lead to a negligible thermal dependency of the cubic lattice parameter below ≃ 40 K. They also affect the dielectricity of BaZrO3 by inducing an overall saturation of the real part of the dielectric response, for temperatures below ≃ 40 K. Two fine structures in the real part, as well as in the imaginary part, of dielectric response are further observed around 50-65 K and 15 K, respectively. Microscopic origins (e.g., unavoidable defects and oxygen octahedra rotation occurring at a local scale) of such anomalies are suggested. Finally, possible reasons for the facts that some of these dielectric anomalies have not been previously reported in the better studied KTaO3 and SrTiO3 incipient ferroelectrics are also discussed.

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International audienceWe report results of a high-pressure investigation by Raman spectroscopy of a classic relaxor ferroelectric (relaxor) PbMg_1/3Nb_2/3O₃ (PMN), which is considered to be a model system for the understanding of relaxor and relaxor-related materials. The observed pressure-dependent Raman spectra are very unusual, pointing to a relaxor-specific spectral signature. We further show that an external pressure of several GPa, as can be met in thin films, alters fundamentally the structural and polar properties of PMN, suggesting that intrinsic instabilities towards pressure play an important role in the reduction of dielectric properties in relaxor and relaxor-related thin films

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We report a neutron and x-ray Rietveld analysis of strontium titanate down to 1.5 K. The results do not show evidence for any supplementary structural phase transition or local frozen polar ordering. These results are a supplementary indication that at very low temperature strontium titanate should display only weak local modifications of the static tetragonal structure with no strong signature in the diffraction pattern.