Integration of thin-film oxide piezoelectrics on glass is imperative for the next generation of transparent electronics to attain sensing and actuating functions. However, their crystallization temperature (above 650 °C) is incompatible with most glasses. We developed a flash lamp process for the growth of piezoelectric lead zirconate titanate films. The process enables crystallization on various types of glasses in a few seconds only. The functional properties of these films are comparable to the films processed with standard rapid thermal annealing at 700 °C. A surface haptic device was fabricated with a 1 μm-thick film (piezoelectric e_33,f of −5 C m⁻²). Its ultrasonic surface deflection reached 1.5 μm at 60 V, sufficient for its use in surface rendering applications. This flash lamp annealing process is compatible with large glass sheets and roll-to-roll processing and has the potential to significantly expand the applications of piezoelectric devices on glass.

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.

The energy of the valence band maximum of ${\mathrm{NaNbO}}_3$ is determined from the Schottky barrier heights at the contacts with low work function Sn-doped ${\mathrm{In}}_2{\mathrm{O}}_3$ and high work function ${\mathrm{RuO}}_2$ by means of x-ray photoelectron spectroscopy with in situ interface preparation. The measurements reveal a valence-band edge energy, which is comparable to that of ${\mathrm{SrTiO}}_3$ and ${\mathrm{BaTiO}}_3$. The energy gap of ${\mathrm{SrTiO}}_3$ and ${\mathrm{BaTiO}}_3$ is $3.2\mathrm{eV}$ and comparable to the values of $3.4\mathrm{eV}\mathrm{to}3.5\mathrm{eV}$, which are determined by means of optical and electron energy loss spectroscopy for ${\mathrm{NaNbO}}_3$. It is therefore expected that the conduction band minimum of ${\mathrm{NaNbO}}_3$ is also located at a similar energy as the conduction band minimum of ${\mathrm{SrTiO}}_3$ and ${\mathrm{BaTiO}}_3$. If this is the case, it can be expected that donor doping of ${\mathrm{NaNbO}}_3$ leads to an electrical conductivity, which is comparable to those of donor-doped ${\mathrm{SrTiO}}_3$ and ${\mathrm{BaTiO}}_3$ (up to $\sim$ $1\mathrm{S}/\mathrm{c}{\mathrm{m}}^{-1}$). In contrast, Sr- and Ca-doped ${\mathrm{NaNbO}}_3$ bulk ceramics exhibit a room temperature conductivity up to $10\times {10}^{-10}\mathrm{S}/\mathrm{c}{\mathrm{m}}^{-1}$, only slightly higher than that of ${\mathrm{NaNbO}}_3$. High-field conductivity measurements and impedance spectroscopy give no indication that the low conductivity is caused by insulating grain boundaries separating electrically conductive grains. It is therefore suggested that the energy gap of ${\mathrm{NaNbO}}_3$ is substantially higher than the gap of $3.4\mathrm{eV}\mathrm{to}3.5\mathrm{eV}$ determined from optical spectroscopy reported in literature and from electron energy loss spectroscopy within this paper, as also suggested from electronic structure calculations of ${\mathrm{LiNbO}}_3$ [ Phys. Rev. B 77, 035106 (2008)].

We report on a heterogeneity study, down to the atomic scale, on a representative multiple-element-modified ceramic based on potassium sodium niobate (KNN): 0.95(Na_0.49K_0.49Li_0.02)(Nb_0.8Ta_0.2)O₃–0.05CaZrO₃ with 2 wt % MnO₂. We show that different routes for incorporating the MnO₂ (either before or after the calcination step) affect the phase composition and finally the functionality of the material. According to X-ray diffraction and scanning electron microscopy analyses, the ceramics consist of orthorhombic and tetragonal perovskite phases together with a small amount of Mn-rich secondary phase. The addition of MnO₂ after the calcination results in better piezoelectric properties, corresponding to a ratio between the orthorhombic and tetragonal perovskite phases that is closer to unity. We also show, using microscopy techniques combined with analytical tools, that Zr-rich, Ta-rich and Mn-rich segregations are present on the nano and atomic levels. With this multi-scale analysis approach, we demonstrate that the functional properties are sensitive to minor modifications in the synthesis route, and consequently to different material properties on all scales. We believe that detecting and learning how to control these modifications will be a step forward in overcoming the irreproducibility problems with KNN-based materials.

Lead-free piezoelectric 0.95(Na_0.49K_0.49Li_0.02)(Nb_0.8Ta_0.2)O₃–0.05CaZrO₃ with 2 wt % MnO₂ addition was prepared using mechanochemically-assisted solid-state synthesis. Upon mechanochemical activation of the mixture of reagents partial amorphization occurs which contributes to a significantly lower temperature of completion of the solid-state reaction, ~600 °C as opposed to ~700 °C for the conventional solid-state synthesis as determined by thermal analysis. The ceramic specimens prepared by the mechanochemically-assisted route exhibit improved compositional homogeneity and slightly enhanced piezoelectric properties, achieved in a considerably shorter processing time compared to the conventional solid-state synthesis route, which was studied as a reference.

We show how sintering in different atmospheres affects the structural, microstructural, and functional properties of ~30 μm thick films of K_0.5Na_0.5NbO₃ (KNN) modified with 0.38 mol% K_5.4Cu_1.3Ta₁₀O₂₉ and 1 mol% CuO. The films were screen printed on platinized alumina substrates and sintered at 1100 °C in oxygen or in air with or without the packing powder (PP). The films have a preferential crystallographic orientation of the monoclinic perovskite phase in the [100] and [−101] directions. Sintering in the presence of PP contributes to obtaining phase-pure films, which is not the case for the films sintered without any PP notwithstanding the sintering atmosphere. The latter group is characterized by a slightly finer grain size, from 0.1 μm to ~2 μm, and lower porosity, ~6% compared with ~13%. Using piezoresponse force microscopy (PFM) and electron backscatter diffraction (EBSD) analysis of oxygen-sintered films, we found that the perovskite grains are composed of multiple domains which are preferentially oriented. Thick films sintered in oxygen exhibit a piezoelectric d₃₃ coefficient of 64 pm/V and an effective thickness coupling coefficient k_t of 43%, as well as very low mechanical losses of less than 0.5%, making them promising candidates for lead-free piezoelectric energy harvesting applications.