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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]

Powder aerosol deposited (PAD) ceramic thick films are a promising candidate for applications in energy storage and energy harvesting. The room-temperature deposition process allows for integration of ceramic films on low-melting substrates, such as stainless steel and polymers, without sintering. Despite this, the dielectric and electromechanical properties vastly differ from bulk ceramics due to internal residual stresses, oxygen defects, and the nano-grained microstructure associated with the deposition process. Although thermal annealing can improve macroscopic properties, precise control of the thermal expansion mismatch between the film and the substrate is required to avoid delamination and film cracking. In this study, we present a method to determine the actual thermal expansion of the film based on the fabrication of freestanding PAD films. Utilizing freestanding films, we demonstrate that dopants and processing conditions such as the carrier gas species directly influence oxygen defects thus modulating the unit cell volume and the conductivity of the oxide film. This is found to be crucial to attain improved dielectric properties within a moderate temperature environment (500 °C) preserving the benefits of the room-temperature deposition process. Additional densification mechanisms are investigated with transmission electron microscopy, scanning electron microscopy, and X-ray microtomography. [ABSTRACT FROM AUTHOR]

Sintering conditions govern the optimized functional properties of ceramics. However, solid-state processing of Bi1/2K1/2TiO3 (BKT), an important end member for lead-free piezoelectric solid solutions suitable for higher temperature (≤ 300 °C) transducer applications, is challenging due to the low melting temperature (≈1070 °C). In this work, the sintering temperature (1030 °C, 1050 °C, and 1060 °C) and dwell time (10 h, 20 h, and 40 h)-dependent functional properties of solid-state processed BKT were investigated, where the sintering condition-dependent dielectric and electromechanical properties were correlated with the variations in crystal structure and microstructure. Although X-ray diffraction data revealed a single-phase tetragonal structure of BKT at room temperature for all sintering conditions, significant changes in both the tetragonal distortion and spontaneous relaxor-ferroelectric transition were observed, which were directly related to the optimized functional properties. In addition, Rayleigh behavior of the piezoelectric coefficient was characterized between −150 °C and 400 °C, demonstrating that the electromechanical response is dominated by the intrinsic contribution, which can be explained by large tetragonal distortion and associated suppression of non-180° domain wall motion. [ABSTRACT FROM AUTHOR]

The room temperature aerosol deposition method is especially promising for the rapid deposition of ceramic thick films, making it interesting for functional components in energy, mobility, and telecommunications applications. Despite this, a number of challenges remain, such as an enhanced electrical conductivity and internal residual stresses in as-deposited films. In this work, a novel technique that integrates a sacrificial water-soluble buffer layer was used to fabricate freestanding ceramic thick films, which allows for direct observation of the film without influence of the substrate or prior thermal treatment. Here, the temperature-dependent chemical and structural relaxation phenomena in freestanding BaTiO3 films were directly investigated by characterizing the thermal expansion properties and temperature-dependent crystal structure as a function of oxygen partial pressure, where a clear nonlinear, hysteretic contraction was observed during heating, which is understood to be influenced by lattice defects. As such, aliovalent doping and atmosphere-dependent annealing experiments were used to demonstrate the influence of local chemical redistribution and oxygen vacancies on the thermal expansion, leading to insight into the origin of the high room temperature conductivity of as-deposited films as well as greater insight into the influence of the induced chemical, structural, and microstructural changes in room temperature deposited functional ceramic thick films. [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]

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]

Aerosol deposition is a feasible method of fabricating dense ceramic films at room temperature by the impact consolidation of submicron‐sized particles on ceramic, metal, glass, and polymer substrates at a rapid rate. Despite the potential usefulness of the aerosol deposition process, there are issues, such as deposition mechanisms and structure of the film‐substrate interface, that are not well understood. We have used complementary structural and microstructural analysis to capture the state of the substrate surface after the aerosol deposition process. The results reveal that modification of the substrate surface by the ejected submicron‐sized particles is essential for the formation of anchoring layer, thereby, a change in internal residual stress state and surface free energy of the substrate is required to deposit film using AD process. Our analysis also suggests that the adhesion between the metal substrate and ceramic particles is possibly contributed by both physical bonding and mechanical interlocking. [ABSTRACT FROM AUTHOR]

This work demonstrates the successful deposition of bioactive glass (BG) 45S5 coatings on various metallic and ceramic substrates at room temperature under low vacuum condition by using aerosol deposition (AD). This room temperature and particle impact consolidation-based deposition method enabled us to deposit well-adhered and dense BG coatings directly on metallic and ceramic substrates. In vitro tests with human osteoblast-like cells on substrates with a 45S5 BG coating demonstrated high cell activity on the surfaces. All tested materials exhibited high in vitro biocompatibility as no inhibition in cell proliferation could be observed. The utilization of AD process for achieving non-crystalline BG coatings is promising for practical bio-medical applications, e.g. , bioactive coatings on bioinert metallic and ceramic substrates. [ABSTRACT FROM AUTHOR]

Abstract The residual stress through the thickness of a BaTiO 3 ceramic film deposited on steel substrate at room temperature with aerosol deposition has been analyzed using synchrotron x-ray microdiffraction. A gradient in stress distribution was evident through the film and the maximum biaxial compressive stress of −800 MPa was observed at the film-substrate interface. Heat-treatment was found to relax the internal compressive stress, due to thermal expansion mismatch between the film and substrate. Variation in ferroelectric response was correlated to the change in stress state by thermal treatment. This analysis is crucial for development of micro-and nanoelectronic devices with AD films. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

In various practical applications, such as high power actuators, high sensitivity sensors, and energy harvesting devices, polycrystalline piezoelectric films of 1–100 µm thickness and sizes ranging from several µm 2 to several cm 2 are required. With conventional film deposition processes, such as sol-gel, sputtering, chemical vapor deposition, or pulsed laser deposition, it is difficult to fabricate films with higher thickness due to their low deposition rate and high interfacial stress. The aerosol deposition method (AD), a relatively new deposition technique, can be used to fabricate highly dense thick films at room temperature by the consolidation of submicrometer-sized ceramic particles on various ceramic, metal, glass, and polymer substrates. Ferroelectric BaTiO 3 ceramic films of different thicknesses ranging from 1 to 30 µm were fabricated on a low-cost metallic substrate at room temperature using the AD method. Surface morphology and adhesion of the film were analyzed. Analysis of internal residual stresses revealed an equibiaxial compressive stress state in the as-processed film. Electrical characterization of films annealed at 500 °C shows an enhanced polarization value of ~ 14 µC/cm 2 over that of the as-processed film. This improved property is related to the decreasing internal residual stress. In addition, the BT films prepared in this work were found to withstand electric fields greater than 100 kV/mm, which is possibly related to the inherent relatively defect-free structure of AD films. [ABSTRACT FROM AUTHOR]

During constrained drying of binder-assisted colloidal coatings on rigid substrates, drying stress-induced defects such as cracks and warpage can often be observed due to the lateral confinement of the film by the substrate. The purpose of the current work is to understand the origin of these drying defects and to develop strategies for their avoidance by the adjustment of slurry composition or processing parameters. In this paper, the time-dependent drying behavior of colloidal ceramic coatings was studied in situ by observation of mass loss, drying shrinkage and drying stress by different methods, such as transparent substrate deflection and beam deflection methods. The stress development and the critical moment, at which cracks form, were investigated in films of different compositions with respect to solvent, particle size, binder and plasticizer. The origins of the measured differences in drying shrinkage, crack formation as well as residual stresses after drying were discussed. [ABSTRACT FROM AUTHOR]

The influence of uniaxial compressive stress on small-signal relative permittivity and direct piezoelectric coefficient of polycrystalline Li-modified (K0.5Na0.5)NbO3 (0, 2, and 4 mol. % Li) was characterized as a function of temperature from 25 to 450 °C. These data reveal corresponding anomalies in both the dielectric and piezoelectric properties near the well-known structural phase transitions in (KxNa1 − x)NbO3. In particular, increasing stress was found to shift the orthorhombic–tetragonal (T O − T ) and tetragonal–cubic (T C) phase boundaries to higher temperatures, thereby stabilizing the lower symmetry phases. Experimental results also show that stress up to a critical value flattens the piezoelectric response below T O − T , above which a monotonic decrease is observed. In contrast, permittivity is increased below T O − T with increasing stress. These results are used to construct a stress–temperature phase diagram of Li-modified (K0.5Na0.5)NbO3. [ABSTRACT FROM AUTHOR]

The macroscopic ferroelastic response of polycrystalline AgNbO 3 was investigated under the uniaxial compressive stress of up to -300 MPa from -150 °C to 450 °C, covering weak ferroelectric, antiferroelectric, and paraelectric phase regions. It is found that AgNbO 3 exhibits ferroelasticity in the weak ferroelectric (M 1), antiferroelectric (M 2 , M 3), as well as the paraelectric regions (O and T), i.e. displaying ferroelastic hysteresis and remnant strain. The changes in mechanical parameters such as coercive stress, back switching strain, and remnant strain values reflect the specific crystal symmetry features at different phase regions together with the influence of temperature on domain wall motion. With stress removed and cooled down to room temperature, X-ray diffraction showed that the sample (at M 1 state) exhibited different degrees of remnant domain textures and lattice strains, depending on its phase state when being compressed. Additionally, in situ stress- and temperature-dependent Raman spectroscopy measurements revealed that uniaxial compressive stress could induce changes in NbO 6 octahedra and cation displacement, especially for high-temperature phases. Overall, the ferroelasticity, effects of stress on the structure and phase transitions offer opportunities for property engineering of AgNbO 3 in capacitor applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Piezoelectric ceramics are envisioned as cell stimulating materials for in-vivo , load-bearing applications. To compensate for their brittle nature developing ceramic films on medically accredited metals is a promising approach. However, high temperature consolidation is often required to achieve highly dense ceramics with suitable functional properties, which can compromise the metal substrate integrity. With aerosol deposition highly dense thick films can be produced at room temperature. Still, an annealing step is required to enhance the functional properties of piezoelectric ceramics. Thermal annealing of dense, aerosol deposited BaTiO 3 thick films on 304SUS stainless steel gave a clear enhancement of the dielectric properties. An increase in saturation polarization and the adoption of ferroelectric hysteresis at 750 °C coincided with a significant reduction in mechanical properties. The simultaneous appearance of grain growth and diffusion of chromium from the substrate at 750 °C suggests that chromium acts as a sintering aid. [Display omitted] • Thermal annealing results in transition from dielectric to ferroelectric polarization hysteresis behavior. • Thermal expansion coefficient mismatch between film and substrate influence quality of annealed film. • Correlation between grain-growth and chromium diffusion from substrate into thick film. [ABSTRACT FROM AUTHOR]

The influence of stress on the phase boundaries of polycrystalline lead-free perovskite (1 − x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 (x = 0.4, 0.5, and 0.6) was characterized through the temperature- and stress-dependent small-signal dielectric and piezoelectric response from − 150 to 200 °C under uniaxial compressive stress up to − 75 MPa. For all three compositions, the phase transition temperatures separating the rhombohedral, orthorhombic, tetragonal, and cubic phases were shifted to higher temperatures with an increase in the uniaxial mechanical loading, corresponding to a significant decrease in the dielectric and piezoelectric responses. Additional stress-dependent relative permittivity measurements up to − 260 MPa were conducted at four different constant temperatures (− 10, 10, 25, and 40 °C), revealing significant increases in the dielectric response, making these materials interesting for tunable dielectric applications. Furthermore, the stress-induced shift in phase transition temperatures was confirmed by in situ combined temperature- and stress-dependent Raman spectroscopy measurements under different constant uniaxial loads within the temperature range from 30 to 130 °C. [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]

The production of advanced functional ceramics from dry raw powders through the solid-state reaction method is a highly industrially relevant process used by numerous researchers and industries around the world. Functional ceramics enable many cutting-edge applications and are, as such, a critical material class. Despite this, the development of high-throughput platforms for accelerated ceramics development from dry powders has not been intensively investigated and has lagged behind other combinatorial technologies, such as solution- and vapor-based systems, due to the complexity of automating the various steps in this powder synthesis route while maintaining the phase purity of resulting materials. As such, there are numerous important opportunities for the accelerated experimental synthesis and characterization of functional ceramics in a high-throughput platform that will allow for the production of large, homogeneous datasets required for machine learning, which will be discussed in this review. In addition, limitations and challenges of the various processing steps will also be presented. [ABSTRACT FROM AUTHOR]

The integration of functional ceramics with metals remains challenging due to the thermally activated processes and the incompatibilities that arise during the high-temperature ceramic sintering process. In order to overcome this, low-temperature processing methods can be employed. In this work, dense 0.9Pb(Mg 1/3 Nb 2/3)O 3 –0.1PbTiO 3 thick films were deposited on low-cost, stainless-steel substrates at room temperature using an aerosol-deposition method. The key material parameters for a successful aerosol deposition of the powder were identified and used in the process, which resulted in homogeneous 15-µm-thick films. The as-deposited films can withstand electric fields of 900 kV⋅cm−1 and exhibit promising room-temperature energy-storage properties: the recoverable energy density reaches 7.0 J⋅cm−3 with an energy-storage efficiency of ∼70%. A post-deposition stress relaxation by annealing at 500°C further improves the recoverable energy density, leading to 9.8 J⋅cm−3 at 900 kV⋅cm−1 with an energy-storage efficiency of ∼80%. The energy-storage performance exhibits excellent temperature stability up to 200°C and an electric-field cycling stability up to 16 million cycles. The low-temperature integration of energy-storage-efficient thick films onto stainless steel opens up possibilities for numerous new, pulsed-power and power-conditioning electronic applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Evolution of spectroscopic properties of a soda–lime silicate glass with different thermal history and under applied uniaxial stress was investigated using Raman and Brillouin spectroscopies as well as Nd3+ photoluminescence techniques. Samples of soda–lime silicate with a cooling rate from 6 × 10−4 to 650 K/min were prepared either by controlled cooling from the melt using a differential scanning calorimeter or by a conventional annealing procedure. Uniaxial stress effects in a range from 0 to −1.3 GPa were investigated in situ by compression of the glass cylinders. The spectroscopic observations of rearrangements in the network structure were related to the set cooling rates or the applied uniaxial stress to calculate an interrelated set of calibrations. Comparing the results from Raman and Brillouin spectroscopy with Nd3+ photoluminescence analysis, we find a linear dependence that can be used to identify uniaxial stress and cooling rate in any given combination concurrently. The interrelated calibrations and linear dependence models are established and evaluated, and equations relating the change of glass network due to effects of cooling rate or uniaxial stress are given. [ABSTRACT FROM AUTHOR]