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The influence of stress on the small‐signal dielectric permittivity and piezoelectric coefficient of polycrystalline lead‐free perovskite 0.92(Na1/2K1/2)NbO3–(0.08 − x)Bi1/2Li1/2TiO3–xBaZrO3 (x = 0, 0.02, 0.04, 0.06, and 0.07) was characterized under different constant uniaxial stress up to −200 MPa within a temperature range of −150 to 450°C, revealing stress‐induced suppression of the electromechanical response as well as shifts in the phase boundaries. For all compositions, the interferroelectric and ferroelectric–paraelectric phase transitions were shifted to higher temperatures under the uniaxial compressive stress. Interestingly, the sensitivity to the applied stress was found to increase with increasing BZ/BLT ratio in the system. The origin of a different extent of stress‐sensitivity with BZ/BLT ratio is suggested to be related to the change in the crystal structure. Additionally, at temperatures below −50°C, the relative permittivity showed a significant increase under applied compressive stress. [ABSTRACT FROM AUTHOR]

Aerosol deposition (AD) is a room‐temperature film deposition method for the fabrication of scalable ferroelectric ceramic films on different substrates, which is particularly appealing for thick film energy storage applications. However, the electrical and mechanical properties of AD ferroelectric films are not yet satisfactorily understood. Here, we report the dielectric, energy storage, and mechanical properties of aerosol‐deposited BaTiO3 (AD‐BT) thick films with nanosized grains by combining macroscopic electric measurements with indentation tests. We find that thermal annealing is an effective way to improve dielectric permittivity and polarization of the AD‐BT film, as well as to increase the hardness and Young's modulus of the film. However, crack formation in the annealed AD‐BT film is promoted in comparison to the as‐processed sample, suggesting that the interplay between the nanosized grains and release of the internal stress during annealing may have major consequences for the mechanical properties and hence should be taken into consideration in application. [ABSTRACT FROM AUTHOR]

External thermal, electrical, and mechanical fields can induce structural phase transitions in lead‐free Li‐modified Na0.5K0.5NbO3 ferroelectrics, which significantly influence the macroscopic electromechanical response. In particular, the relative stability of the polar monoclinic (or orthorhombic) and tetragonal phases under temperature and stress is critical to realize the ferroelectric and piezoelectric response. In this study, the effect of mechanical and thermal fields on the local structure in the vicinity of the monoclinic‐tetragonal (M‐T) phase boundary was investigated using a novel in situ combined uniaxial compressive stress‐ and temperature‐dependent Raman spectroscopy experimental arrangement. Experiments were performed up to 300°C and −200 MPa, clearly demonstrating stress‐induced M‐T phase transition in Li‐modified Na0.5K0.5NbO3. A stress‐temperature phase diagram has been established based on the change in vibrational modes. It was possible to correlate the relative permittivity singularities previously observed to a given stage of the M‐T phase transition using ratio between characteristic Raman band areas. In addition, the measurement method reported here can be applied to other functional ceramics to investigate the influence of mechanical fields on local structure. [ABSTRACT FROM AUTHOR]

External thermal, electrical, and mechanical fields can induce structural phase transitions in lead‐free Li‐modified Na0.5K0.5NbO3 ferroelectrics, which significantly influence the macroscopic electromechanical response. In particular, the relative stability of the polar monoclinic (or orthorhombic) and tetragonal phases under temperature and stress is critical to realize the ferroelectric and piezoelectric response. In this study, the effect of mechanical and thermal fields on the local structure in the vicinity of the monoclinic‐tetragonal (M‐T) phase boundary was investigated using a novel in situ combined uniaxial compressive stress‐ and temperature‐dependent Raman spectroscopy experimental arrangement. Experiments were performed up to 300°C and −200 MPa, clearly demonstrating stress‐induced M‐T phase transition in Li‐modified Na0.5K0.5NbO3. A stress‐temperature phase diagram has been established based on the change in vibrational modes. It was possible to correlate the relative permittivity singularities previously observed to a given stage of the M‐T phase transition using ratio between characteristic Raman band areas. In addition, the measurement method reported here can be applied to other functional ceramics to investigate the influence of mechanical fields on local structure. [ABSTRACT FROM AUTHOR]

Aerosol deposition (AD) is a dynamic loading process that can be envisioned as a shock wave loading, necessitating the consideration of the elastic/plastic response of solid materials. Due to the dynamic nature of this process, however, experimental determination of the local pressures during the deposition process is difficult. This work addresses this by investigating the compression and subsequent structure modification of a silicate glass after room‐temperature AD on a silicate glass substrate with Raman spectroscopy. Clear structural changes in the short‐ and middle‐range order of the silicate glass were observed, both as intertetrahedral angle distribution and as ring statistic. Therefore, the AD induced permanent densification of the glass, equivalent, in a hydrostatic approximation, to a minimal pressure of 10.5 ± 1.5 GPa during the film deposition process. Furthermore, the analysis of the Nd3+ photoluminescence of the 4F3/2 − 4I9/2 transition provided complementary information on the glass network modifications occurring during film formation. More than a pure hydrostatic densification, the AD seems to present a very intense shear deformation. This work opens up the perspective of evaluating the mechanical response of film‐substrate and of the particles themselves, and provides critical information on the mechanisms responsible for the AD film formation. [ABSTRACT FROM AUTHOR]

A novel technique for the rapid room‐temperature deposition of porous ceramic, glass, or metal thick films using the aerosol deposition (AD) method is presented. The process is based on the co‐deposition of the desired film material and a second water‐soluble constituent, resulting in a ceramic‐ceramic composite. Following the subsequent removal of water‐soluble end member, a network of pores is retained. To demonstrate the process, porous BaTiO3 thick films were fabricated through co‐deposition with NaCl. Microstructural images show the clear development of a porous structure, which was found to enhance the dielectric properties over dense thick films, possibly related to the lower extent of internal residual stress. This simple but highly effective porous structure fabrication can be applied to any film and substrate material stable in water and is promising for the application of AD‐processed films in gas sensors, solid oxide fuel cells, and humidity sensors. [ABSTRACT FROM AUTHOR]