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The hydrothermal synthesis of SrTiO3 in a Sr­(OH)2/NaOH solution by reaction of four different single crystalline titanium precursors (anatase, rutile, sodium titanate, and hydrogen titanate) having the same nanowire morphology was investigated under stagnant fluid conditions. Owing to the low solubility and dissolution rate of the parent phases, the reaction mainly occurs in a thin interfacial fluid layer. The new phase only grows on the substrate surface, and the morphology evolution is largely controlled by the interface through the coupling of substrate dissolution and SrTiO3 crystallization. The pseudomorphic replacement of the precursor by the product occurs if complete surface coverage is attained. Depending on the crystallographic matching, the parent crystal can either transform in a mesocrystal as happens with anatase via a topochemical transformation or in a polycrystalline product as observed with sodium titanate. In contrast, if the product grows in the form of isolated particles or with dendritic morphology, as in the case of hydrogen titanate and, to a lesser extent rutile, the new compound will not inherit the precursor morphology. When well-defined interfaces are missing, as happens when amorphous titanium hydroxide gel suspensions are used as precursors, the crystallization of SrTiO3 occurs by a completely different pathway, i.e., oriented self-assembly of nanocrystals in mesocrystals.

BaSnxTi1−xO3 solid solutions with compositions in the range x = 0–0.20 were studied by combining analysis of the field-induced dielectric and ferroelectric properties with Raman spectroscopic investigations. By combining techniques, the detection of specific features related to the ferroelectric-to-relaxor crossover with increasing Sn content is possible. Detailed tunability analysis of the x = 0.05 composition indicated that multiple components contribute to the dc-field induced permittivity response; these components are active in different temperature and field ranges and could be assigned to a few polarization mechanisms. First order reversal curves (FORC) for the material clearly show a transition from ferroelectric-to-relaxor behavior with increasing x, confirming the conclusions from the Raman and dielectric studies. This was evidenced by the shift of the FORC distribution over coercivities toward zero field values. Raman measurements allow the identification of the separate phases with varying Sn content and temperature, indicating large regions of phase coexistence. The composition x = 0.20 is in a predominantly relaxor state. This is ascribed to a large range of phase coexistence and to the presence of polar nanoregions promoted by Sn substitution on the B site of the perovskite unit cell ABO3.

The grain size influence on the dielectric relaxation and nonlinear dielectric properties of BaTiO 3 ceramics with grain size in the range of (92Ä936) nm densified by Spark Plasma Sintering (SPS) from ultrafine powders were investigated. The progressive reduction of the Curie temperature and of the effective permittivity results from a combination of intrinsic size effects and low-permittivity grain boundary layer. A model of dielectric cylindrical cavities was employed in order to calculate intrinsic effective permittivity values in GHz range. An interesting feature is the presence of a thermally activated Debyelike relaxation in the ferroelectric state of ceramics with grain size above 300 nm, with activation energies of 0.45-0.49 eV, which seems to be related to the domain walls forced motion under the applied field. By diminishing grain size, a progressive reduction of the ferroelectric nonlinear character was obtained, reaching a macroscopic non-switching character and a linear permittivity versus field dependence for the finest ceramics (grain size of 90-100 nm) until very high values of the applied field. The observed behavior supports the idea of frozen polarization induced by pinning centers as due to a large number of grain boundaries and charged defects in the fine structures.

In this work, an improved version of the radio frequency magnetron sputtering (RF-MS) technique was used to prepare highly adherent B-type carbonated hydroxylapatite (B-CHA) thin films. Fourier transform infrared spectroscopy (FTIR) and grazing incidence X-ray diffraction studies proved that the coatings maintained the composition and revealed the polycrystalline structure of HA. Scanning electron microscopy analysis showed that the CHA films are rough and exhibit a homogeneous microstructure. Energy-dispersive X-ray spectroscopy (EDX) mapping demonstrated a uniform distribution of the Ca and P cations while a Ca/P ratio of 1.8 was found. In addition, the FTIR experiments showed a remarkable reproducibility of the nanostructures. Human mesenchymal stem cells (hMSCs), in vitro differentiated osteoblasts, and explanted bone cells were grown over the surface of CHA coatings for periods between a few hours and 21 days. Osteoprogenitor cells maintained viability and characteristic morphology after adhesion on CHA coatings. Ki67-positive osteoblasts were the evidence of cell proliferation events. Cells showed positive staining for markers of osteoblast phenotype such as collagen type I, bone sialoprotein and osteonectin. Our data showed the formation of mineralized foci by differentiation of hMSCs to human primary osteoblasts after cultivation in osteogenic media on RF-sputtered films. The results demonstrate the capacity of B-type CHA coating to support MSCs adhesion and osteogenic differentiation ability.