Pietro Galizia

Elastic aging from coexistence and transformations of ferroelectric and antiferroelectric states in PZT

Materials undergoing antiferroelectric/ferroelectric (AFE/FE) transitions are studied for possible applications that exploit the large volume, charge, and entropy differences between the two states, such as electrocaloric cooling, energy storage, and electromechanical actuators. Though certain compositions of PbZr1−xTixO3 codoped with La and Sn may withstand millions of electrically induced AFE/FE cycles, in other cases few thermally induced cycles and room temperature aging may cause noticeable changes in the material properties. This is particularly evident in the elastic moduli, which at room temperature can become as much as four times softer. In order to get more insight into the mechanisms involved in such elastic aging and full recovering with mild annealing at 600–800 K, the effect of La doping on PbZr0.954Ti0.046O3 is studied with anelastic measurements. Complete suppression of the time dependent phenomena is found after the transformation of the intermediate FE phase into incommensurate AFE by 2...

On the thermal shock resistance and mechanical properties of novel unidirectional UHTCMCs for extreme environments

Aerospace provides a strong driving force for technological development. Recently a novel class of composites for harsh environments, based on ultra-high temperature ceramic composites reinforced with continuous fibers (UHTCMC), is being developed. The goal of this work is to overcome the current data patchwork about their microstructural optimization and structural behavior, by showing a consistent mechanical characterization of well-defined and developed UHTCMCs based on ZrB2-matrix. The obtained composites have a density of 3.7 g/cm3 and porosity of less than 10%. The flexural strength increased from 360 to 550 MPa from room temperature to 1500 °C, showing a non-brittle behaviour. The composites were able to sustain a thermal shock severity as high as 1500 °C. The maximum decrease of strength at 1400 °C was 16% of the initial value, indicating that the samples could be shocked at even higher temperature. Flexural strength, Young’s modulus and coefficient of thermal expansions (CTE) of the composites were measured both along transverse and longitudinal direction and correlated to the microstructural features. The presented microstructural and mechanical characterization well defines the potentiality of the UHTCMCs and can be used as reference for the design and development of novel thermal protection systems and other structural components for harsh environments.

Processing and characterization of screen printing Ba0.5Sr0.5Co0.8Fe0.2O3−δ inks

Oxygen-selective membranes based on thin layers of barium–strontium–cobalt ferrite Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) perovskite oxide were manufactured. Five BSCF inks prepared with different carriers and milling treatments were rheologically characterized, screen printed on three different porous alumina substrates and sintered at 1050 and 1150∘C. The resulting membranes were characterized. The data collected on the rheological properties of inks (flow curves, thixotropic behaviour, linear viscoelasticity), their processability by screen printing, and the quality of the layers obtained after sintering represents an important starting point to set up the next research activities.

Titania-cobalt ferrite ceramic composites for high frequency magnetic applications

New magneto-dielectric cobalt ferrite (CFO)- titania (TO) ceramic in situ composites were prepared by reactive sintering. Magnetic permeability was investigated and correlated to the microstructure of the sintered ceramic composite bodies. We have obtained highly densified ceramic composites with CFO dispersed in two different dielectric matrices. The formation of a new ternary compound Fe₂CoTi₃O₁₀ (FCTO) or a mixture of CoTiO₃ (CTO) and Fe₂O₃ (FO) as dielectric phases could be produced by varying the molar ratio of the TO and CFO starting mixture.

Electrophoretic deposition of bilayer based on sacrificial titanium dioxide and lead zirconate titanate on bare silicon wafer

Bilayer thick films of sacrificial titanium dioxide and Nb-doped lead zirconate titanate (PZTN) have been deposited on bare silicon wafers using electrophoretic deposition (EPD) technique. Deposition of such ceramic particles, dispersed ethanol-based suspensions, on semiconductor substrate has been made possible after preparation of alloyed junctions Al/Si characterized by ohmic behaviour. Sintering of green TiO2/PZTN films was performed at 900 °C for 1 h. The composition of the films, the thickness and relative density of the deposited materials have been analysed by EDS-SEM analysis. The lead diffusion through the silicon wafer has been reduced.