Nanoscale Piezoelectric Properties and Phase Separation in Pure and La-Doped BiFeO3 Films Prepared by Sol-Gel Method.

Pure BiFeO3 (BFO) and doped Bi0.9La0.1FeO3 (BLFO) thin films were prepared on Pt/TiO2/SiO2/Si substrates by a modified sol-gel technique using a separate hydrolysis procedure. The effects of final crystallization temperature and La doping on the phase structure, film morphology, and nanoscale piezoelectric properties were investigated. La doping and higher crystallization temperature lead to an increase in the grain size and preferred (102) texture of the films. Simultaneously, a decrease in the average effective piezoelectric coefficient (about 2 times in La-doped films) and an increase in the area of surface non-polar phase (up to 60%) are observed. Phase separation on the films' surface is attributed to either a second phase or to a non-polar perovskite phase at the surface. As compared with undoped BFO, La-doping leads to an increase in the average grain size and self-polarization that is important for future piezoelectric applications. It is shown that piezoelectric activity is directly related to the films' microstructructure, thus emphasizing the role of annealing conditions and La-doping that is frequently used to decrease the leakage current in BFO-based materials.

Mn-Doped BaTiO3Ceramics: Thermal and Electrical Properties for Multicaloric Applications.

Multiferroic materialsare widely used in microelectronics because they are sensitive to elastic, magnetic, and electric fields and there is an intrinsic coupling between them. In particular, transition metal-doped BaTiO3 is consideredas a viable multiferroic because of the simultaneous presence of ferroelectricity and magnetism.In this work, we study the electrical and thermal properties of Mn-doped BaTiO3 ceramics that can be used for multicaloric applications. We found that Mn doping leads to the broadening and shifting of the phase transition accompanied with simultaneous decrease of latent heat and entropy. Mn doping causes a decrease in the bulk resistivity while contact resistance remains intact. Doped ceramics can withstand high electric fields(up to 40 kV/cm) and exhibit linear I-V characteristics followed by the Schottkylimited current in contrast to earlier observations. As such, these ceramics are promising for multicaloric applications.

Low-Frequency Vibration Energy Harvesting With Bidomain LiNbO3 Single Crystals.

Low-frequency vibration energy harvesting is becoming increasingly important for environmentally friendly and biomedical applications in order to power various wearable and implanted devices. In this paper, we propose the use of piezoelectric congruent LiNbO3 (LN) single crystals, with an engineered bidomain structure, as an alternative to the widely employed lead-based PZT. We thus compared experimentally the pure vibration energy scavenging performance of square-shaped bidomain and single-domain Y+128°-cut LN crystals and a conventional bimorph soft PZT ceramic bonded to long spring-steel cantilevers as a function of the frequency, load resistance, and tip proof mass. At a low bending resonance frequency of ca. 32.2 Hz, the bidomain LN yielded an open-circuit voltage of 1.54 kV/g, almost one order of magnitude larger than that observed in PZT. The maximum extractable average power was found to be of 9.2 mW/g2 in the bidomain LN, 6.2 mW/g2 in the single-domain LN, and 1.8 mW/g2 in the PZT piezo-elastic cantilevers. With five times higher output power density of up to 11.0 mW/(cm [Formula: see text]) under resonance conditions, bidomain LN was thus shown to be a reliable lead-free and high-temperature alternative to PZT, thanks to its considerably larger quality factor and electromechanical conversion efficiency.

An atomic force microscopy mode for nondestructive electromechanical studies and its application to diphenylalanine peptide nanotubes.

Nondestructive scanning probe microscopy of fragile nanoscale objects is currently in increasing need. In this paper, we report a novel atomic force microscopy mode, HybriD Piezoresponse Force Microscopy (HD-PFM), for simultaneous nondestructive analysis of piezoresponse as well as of mechanical and dielectric properties of nanoscale objects. We demonstrate this mode in application to self-assembled diphenylalanine peptide micro- and nanotubes formed on a gold-covered substrate. Nondestructive in- and out-of-plane piezoresponse measurements of tubes of less than 100 nm in diameter are demonstrated for the first time. High-resolution maps of tube elastic properties were obtained simultaneously with HD-PFM. Analysis of the measurement data combined with the finite-elements simulations allowed quantification of tube Young's modulus. The obtained value of 29 ±â€¯1 GPa agrees well with the data obtained with other methods and reported in the literature.

AN69 hollow fiber membrane will reduce but not abolish the risk of transmission of porcine endogenous retroviruses.

As the risk of porcine endogenous retrovirus (PERV) infection is a major obstacle to the xenotransplantation of porcine tissue, we investigated whether an AN69 hollow fibre membrane, used for islets of Langerhans transplantation, could prevent the transfer of PERVs and thus reduce the risk of PERV infection. PK15 cells were used as a PERV source. A specific and highly sensitive RCR was used for detection of a PERV provirus DNA (gag region) and a porcine mtDNA. Human U293 cells were incubated in vitro with encapsulated PK15 cells, concentrated encapsulated PK15 supernatant, or concentrated PK15 supernatant as a control. CD1 mice were implanted in vivo with encapsulated PK15 cells or injected with PK15 supernatant. We found no infection in human cells incubated with either encapsulated PK15 supernatant or in 10 out of 11 samples after coincubation with encapsulated PK15 cells. Infection of human cells was, however, detected in 1 out of 11 samples after coincubation with encapsulated PK15 cells. The presence of PERV provirus DNA and porcine mtDNA was detected in all the investigated tissues of the mice injected with PK15 supematant and in various tissues of the mice implanted with encapsulated PK15 cells. Four weeks after the last injection of PK15 supernatant or a fiber explantation, no mouse showed any presence of PERV provirus DNA or porcine mtDNA. Our results demonstrate that AN69 hollow fiber membrane will reduce but not abolish the risk of PERV infection. Because the real risk of PERV infection still remains unknown, it is necessary to investigate further the real protection that could be provided by hollow fibers to ensure the safety of clinical xenotransplantation.

Insulin treatment of mice recipients preserves beta-cell function in porcine islet transplantation.

Encapsulation of islets of Langerhans confers protection against cell-mediated immune destruction and so should allow the transplantation of islets without immunosuppression. Xenotransplantation of encapsulated islets of Langerhans might therefore help overcome problems of human organ donor shortage. Given that islets exposed to sustained hyperglycemia show impaired beta-cell function, we set out to determine whether recipient treatment with insulin could improve transplantation success rate. Islets of Langerhans were obtained from Specific Germ-Free (SPF) pig pancreas and cultured overnight. Islets were encapsulated in AN69 fibers and implanted into the peritoneal cavity of diabetic mice. A group of implanted mice was treated with exogenous insulin from day 3 to day 7 after grafting. Islet implantation depressed plasma glucose in all the mice, both insulin treated and untreated. Glycemia slowly increased in the non-insulin-treated mice, whereas the decrease observed in the insulin-treated mice was maintained until day 29 of follow-up. We found significant differences between the two groups (p < 0.05 at day 18 and day 20, p < 0.001 at day 23 and day 29). No improvement of hyperglycemia was observed in diabetic mice implanted with empty fibers. When islet-containing fibers were removed from the peritoneal cavity of mice 1 month after the graft plasma glucose increased markedly. We demonstrate that treatment of recipients with exogenous insulin in the immediate posttransplantation period has a positive effect on beta-cell function in transplanted macroencapsulated porcine islets.