Chemical Solution Deposition of Barium Titanate Thin Films with Ethylene Glycol as Solvent for Barium Acetate

Chemical solution deposition (CSD) of BaTiO3 (BT) or BT-based thin films relies on using a carboxylic acid and alcohol as the solvents for alkaline-earth carboxylate and transition-metal alkoxide, respectively; however, the esterification reaction of the solvents may lead to in-situ water formation and precipitation. To avoid such an uncontrolled reaction, we developed a route in which ethylene glycol (EG) is used as the solvent for Ba-acetate. The EG-based BT coating solutions are stable for at least a few months. The thermal decomposition of the BT xerogel obtained by drying the EG-based solutions depends on the choice of the solvent for the Ti-alkoxide as well: in the case of EG and 2-methoxyethanol solvents carbon residues are removed at only about 1100 °C, while in the case of ethanol it is concluded at about 700 °C. About 100 nm thick BT films derived from the EG-ethanol solution deposited on platinized silicon reveal dense, crack-free columnar microstructure. They exhibit local ferro- and piezoelectric properties. The macroscopic polarization-electric field loops were obtained up to a quite high electric field of about 2.4 MV/cm. The EG-ethanol based CSD route is a viable alternative to the established acetic acid–alcohol route for BT and BT-based films

Evaluation of the homogeneity in Pb(Zr,Ti)O3–zirconia composites prepared by the hetero-agglomeration of precursors using the Voronoi-diagram approach

Hetero-agglomeration of precursor particles was employed to achieve a homogeneous distribution of tetragonal zirconia (TZ) grains within a lead zirconate titanate (PZT) ceramic matrix. The surface charge of the zirconia particles in the aqueous suspension was modified by the addition of citric acid. At pH 5, the citric-acid-modified TZ particles were negatively charged, while the PZT particles were positively charged, which led to the agglomeration of the two types of particles. The homogeneity of the TZ distribution in the PZT–TZ ceramic composites prepared from the hetero-agglomerated particles was evaluated using Voronoi-diagram analyses. The results showed that the homogeneity of the composites prepared using the citric-acid-modified TZ particles was higher than in the case where the TZ particles were not modified. The curves for the crack-growth resistance were also determined in order to investigate the impact of particle homogeneity on the fracture behavior

Compositional Dependence of R-curve Behavior in Soft Pb(Zr1−xTix)O3 Ceramics

The compositional dependent fracture behavior of soft PZT (Pb0.99Ba0.01(Zr1−xTix)0.98Nb0.02O3) ceramics in the vicinity of the morphotropic phase boundary was characterized using compact-tension specimens. The compositions with 0.40 ≤ x ≤ 0.55 displayed an increasing fracture resistance with crack extension (R-curve behavior). It was observed that the rhombohedral composition and the compositions near the morphotropic phase boundary showed the largest toughness enhancement. R-curve behavior was found to be influenced by the ferroelastic coercive stress, saturated remanent strain, and elastic modulus, which were experimentally measured for each composition. X-ray diffraction measurements were performed and compared to the fracture results to investigate the impact of phase and lattice distortion on ferroelastic toughening behavior

Sintering of Lead-Free Piezoelectric Sodium Potassium Niobate Ceramics

The potassium sodium niobate, K0.5Na0.5NbO3, solid solution (KNN) is considered as one of the most promising, environment-friendly, lead-free candidates to replace highly efficient,lead-based piezoelectrics. Since the first reports of KNN, it has been recognized that obtaining phase-pure materials with a high density and a uniform, fine-grained microstructure is a major challenge. For this reason the present paper reviews the different methods for consolidating KNN ceramics. The difficulties involved in the solid-state synthesis of KNN powder, i.e., obtaining phase purity, the stoichiometry of the perovskite phase, and the chemical homogeneity, are discussed. The solid-state sintering of stoichiometric KNN is characterized by poor densification and an extremely narrow sintering-temperature range, which is close to the solidus temperature. A study of the initial sintering stage revealed that coarsening of the microstructure without densification contributes to a reduction of the driving force for sintering. The influences of the (K + Na)/Nb molar ratio, the presence of a liquid phase, chemical modifications (doping, complex solid solutions) and different atmospheres (i.e., defect chemistry) on the sintering are discussed. Special sintering techniques, such as pressure-assisted sintering and spark-plasma sintering, can be effective methods for enhancing the density of KNN ceramics. The sintering behavior of KNN is compared to that of a representative piezoelectric lead zirconate titanate (PZT)

Simultaneous Enhancement of Fracture Toughness and Unipolar Strain in Pb(Zr,Ti)O3-ZrO2Composites Through Composition Adjustment

The influence of second phase zirconia particles on the electrical properties and fracture behavior of various polycrystalline soft Pb(Zr1−xTix)O3 (PZT) compositions was investigated. PZT composites with yttria-stabilized tetragonal zirconia particles exhibited enhanced crack resistance in comparison to monolithic compositions, regardless of the PZT composition. The addition of zirconia, however, was found to change the PZT composition through the diffusion of zirconium, resulting in variations in the observed piezoelectric and ferroelectric responses. Through the tailoring of the PZT matrix composition, the large electromechanical response and enhanced fracture toughness could be retained. The variation in both small and large signal properties is contrasted to fracture results and crystal structure changes, as determined by X-ray diffraction

Atomic-Level Response of the Domain Walls in Bismuth Ferrite in a Subcoercive-Field Regime

The atomic-level response of zigzag ferroelectric domain walls (DWs) was investigated with in situ bias scanning transmission electron microscopy (STEM) in a subcoercive-field regime. Atomic-level movement of a single DW was observed. Unexpectedly, the change in the position of the DW, determined from the atomic displacement, did not follow the position of the strain field when the electric field was applied. This can be explained as low mobility defect segregation at the initial DW position, such as ordered clusters of oxygen vacancies. Further, the triangular apex of the zigzag wall is pinned, but it changes its shape and becomes asymmetric under electrical stimuli. This phenomenon is accompanied by strain and bound charge redistribution. We report on unique atomic-scale phenomena at the DW level and show that in situ STEM studies with atomic resolution are very relevant as they complement, and sometimes challenge, the knowledge gained from lower resolution studies

R-curves in transformation toughened lead zirconate titanate

Composites from lead zirconate titanate (PZT) and yttria stabilized zirconia were manufactured to assess cracking and R-curve behavior in compact tension specimens. Additions of zirconia led to a reduction in PZT grain size and shifted the fracture behavior from intergranular fracture to intragranular fracture. The R-curves exhibited higher starting values, a steeper slope and a higher plateau value with increasing content of zirconia, albeit the effects on the toughness values were not more than 20%. The results are rationalized through increased crack tip toughness, reduced ferroelastic toughening and enhanced transformation toughening