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Ferroelectric materials with Bi-layered structure such as SrBi2Ta2O9 and SrBi2Nb2O9 are now intensively investigated in view of their applications in nonvolatile computer memories and high-temperature piezoelectric transducers. When Sr2+ is substituted with Ba2+, a significant disorder is induced and the material exhibits broadening of the phase transition. Such broadening is essential for applications since it allows achieving smooth temperature characteristics while maintaining high dielectric and piezoelectric properties. In this work, stoichiometric dense BaBi2Nb2O9 (BBN) ceramics are sintered using a mixed oxide route. Dielectric and ferroelectric properties are investigated in a broad range of temperatures and frequencies. Strong dispersion of the complex relative dielectric permittivity is observed including typical relaxor features such as shift of the permittivity maximum with frequency and broadening of the relaxation time spectrum with decreasing temperature. The dielectric relaxation obeys the Vögel–Fulcher relationship with anomalously low freezing temperature (Tf≈100 K), which is much lower than the permittivity maximum in the radio-frequency range. Polarization hysteresis loops testify linear properties of BBN at all temperatures above Tf. The properties of BBN ceramics are compared to conventional relaxor systems such as Pb(Mg, Nb)O3 and (Pb, La)(Zr, Ti)O3.

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The relationship between charge transport, defects and ferroelectric response is established for K0.5Na0.5NbO3 (KNN) and Mn-doped KNN ceramics. At room temperature the conduction in KNN is associated with hole transport and can be suppressed by Mn doping. Because of that a less leaky ferroelectric hysteresis loop is obtained for Mn-doped KNN. At high temperatures the conduction is dominated by the motion of ionized oxygen vacancies, the concentration of which increases with Mn doping. This work adds relevant information on KNN and leverages its potential application.

Hydroxyapatite (Hap) is a calcium phosphate with a chemical formula that closely resembles that of the mineral constituents found in hard tissues, thereby explaining its natural biocompatibility and wide biomedical use. Nanostructured Hap materials appear to present a good performance in bone tissue applications because of their ability to mimic the dimensions of bone components. However, bone cell response to individual nanoparticles and/or nanoparticle aggregates lost from these materials is largely unknown and shows great variability. This work addresses the preparation and characterization of two different Hap nanoparticles and their interaction with osteoblastic cells. Hap particles were produced by a wet chemical synthesis (WCS) at 378C and by hydrothermal synthesis (HS) at 1808C. As the ultimate in vivo applications require a sterilization step, the synthesized particles were characterized 'as prepared' and after sterilization (autoclaving, 1208C, 20 min). WCS and HS particles differ in their morphological (size and shape) and physicochemical properties. The sterilization modified markedly the shape, size and aggregation state of WCS nanoparticles. Both particles were readily internalized by osteoblastic cells by endocytosis, and showed a low intracellular dissolution rate. Concentrations of WCS and HS particles less than 500 mg ml 21 did not affect cell proliferation, F-actin cytoskeleton organization and apoptosis rate and increased the gene expression of alkaline phosphatase and BMP-2. The two particles presented some differences in the elicited cell response. In conclusion, WCS and HS particles might exhibit an interesting profile for bone tissue applications. Results suggest the relevance of a proper particle characterization, and the interest of an individual nanoparticle targeted research.