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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]

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]

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]

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]

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 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]