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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]

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 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 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]