Neutron powder diffraction was used in operando to determine the macroscopic strain and piezoelectric coefficient as a function of applied electric field in a technically relevant actuator material. We were able to individually investigate the two coexisting phases in the material and reveal the origin of maximized strain at phase boundaries. Insight into the strain mechanisms with unprecedented detail gives evidence that, on average, the classic inverse piezoelectric effect does not apply for polycrystalline materials.

Piezoelectric thin films are of current interest in science and industry for highly integrated nano-electro-mechanical-systems and sensor devices. In this study, the dependence of the piezoelectric properties on the doping concentration in Si:HfO2 thin films and their crystallographic origin are investigated. The Si:HfO2 films with a thickness of 20 nm and various Si doping concentrations in the range of 2.7–5.6 cat.% were examined. The relationship between the piezoelectric displacement and remanent polarization is studied during wake-up from the antiferroelectric-like pristine state until the cycled ferroelectric state, which reveals an application-dependent optimal doping concentration. Furthermore, the piezoelectric and ferroelectric properties, as well as the relative permittivity, were measured over wake-up, thus giving a glimpse at the underlying mechanism of the transition from a pristine antiferroelectric-like behavior to a ferroelectric/piezoelectric one, revealing a pre-existing polar phase that is reorienting during wake-up. The studied samples show a strong displacement and polarization dependence on the doping concentration. Hence, the stoichiometry is an excellent parameter for the application-specific adjustment of complementary metal–oxide–semiconductor compatible piezoelectric thin films.

The in‐plane piezoelectric response of 20 nm thick Si‐doped HfO2 is examined by exploiting thermal expansion of the substrate upon rapid temperature cycling. The sample is heated locally by a deposited metal film, and the subsequently registered pyroelectric current is found to be frequency dependent in the observed range of 5 Hz to 35 kHz. While the intrinsic response remains constant, the secondary contribution can be switched off in the high‐frequency limit due to substrate clamping. As this secondary response is generated by thermal expansion and the piezoelectric effect, this allows for extraction of the corresponding in‐plane response. By comparing pyroelectric measurements in low‐ and high‐frequency limits, a piezoelectric coefficient d31 of −11.5 pm V −1 is obtained, which is more than five times larger than that of AlN. The magnitude of piezoelectric response increases upon electric field cycling, which is associated with a transition from antiferroelectric‐like behavior to a purely ferroelectric polarization hysteresis. The hafnium oxide material system is proposed as a promising candidate for future CMOS compatible piezoelectric micro‐ and nano‐electromechanical systems (MEMS and NEMS).

The accurate determination of electrocaloric coefficients in nanometer-thin, polycrystalline doped HfO2 is challenging and has led to very different values reported in the literature. Here, we apply two different methods in order to compare and analyze reversible and irreversible or metastable contributions to the electrocaloric effect. The indirect method is based on temperature-dependent ferroelectric hysteresis characteristics. Furthermore, we apply a direct method, where electrocaloric temperature variations are observed using a specialized test structure. A comparison of both methods reveals that the indirect method dramatically overestimates the response due to thermal fatigue effects, which are caused by the migration of charged defects to the electrode interfaces. The partial transition to the antiferroelectric-like tetragonal phase is not immediately reversed to the polar Pca21 phase upon cooling. An electrocaloric coefficient of −107 μC m−2 K−1 is determined for a 20 nm thick Si-doped HfO2 film with the direct method, which corresponds to a ΔT of 4.4 K.

Advanced, costeffective and series compatible manufacturing of active structural components demands for short production times and complex multi-material designs. Highest efficiency is achieved when integrating the poling process of the piezoceramic that activates the piezoelectric effect into the manufacturing chain. The present paper reports on first results of the systematic evaluation of parameters governing the poling regime of commercial lead zirconate titanate (PZT) ceramics. It aims to find the conditions for efficient poling of the active material as an integrated technology step in mass production. In the present investigation, the influence of poling field strength and temperature on the obtained remanent polarization is considered by varying the temperature from -175 °C to 150 °C and the electric poling field strength from 1.0 to 2.0 kV/mm. Six commercially available piezoceramic materials, primarily used in actuator applications, were investigated. From the findings, it was possible to deduce technological parameters for an efficient poling process