Electrophoretic deposition and properties of strontium-doped sodium potassium niobate thick films

Comparative analysis of bulk ceramics and thick film coatings for optimized energy storage technologies

The present investigation provides an easy and affordable strategy for fabrication of functional ceramics Bi0.5Na0.5TiO3-SrFe12O19 (BNT-SrF5) thick films on a flexible, inexpensive and electrically integrated substrate using electrophoretic deposition process (EPD). EPD is a widely accepted, environmentally friendly method for applying coatings from a colloidal suspension to conductive substrates. Lead-free ferroelectric BNT-SrF5 powder was synthesized by solid state method to fabricate bulk samples and thick films (30-160 μm) by EPD process. Thick films were deposited onto nickel substrate by applying EPD parameters, i.e. voltage (225-290 V) and coating time (30-180 s) to acetone based colloidal suspension without aid of any dispersing agent. In a comparative analysis, both thick films and bulk ceramics revealed significant densification with sintering temperature from 1025 to 1150 °C. Fourier transform Infrared (FTIR) and X-ray diffraction (XRD) analysis revealed presence of distorted perovskite structure following calcination and sintering processes. Scanning electron microscopy (SEM) provided the surface morphologies of BNT-SrF5 powder. The dielectric constant of film sample revealed more thermal stable response compared to the bulk ceramics. Impedance spectroscopy explained the electrically active regions and hopping conduction mechanism which witnessed NTCR behavior. The potential applications for the miniaturization of electronics are sensors, actuators and energy harvesting devices.

Lead-Free Sodium Potassium Niobate-Based Multilayer Structures for Ultrasound Transducer Applications

Thick films with nominal composition (K₀.₅Na₀.₅)₀.₉₉Sr₀.₀₀₅NbO₃ (KNNSr) on porous ceramics with identical nominal composition were investigated as potential candidates for environmentally benign ultrasonic transducers composed entirely of inorganic materials. In this paper, the processing of the multilayer structure, namely, the thick film by screen printing and the porous ceramic by sacrificial template method, is related to their phase composition, microstructure, electromechanical, and acoustic properties to understand the performance of the devices. The ceramic with a homogeneous distribution of 8 μm pores had a sufficiently high attenuation coefficient of 0.5 dB/mm/MHz and served as an effective backing. The KNNSr thick films sintered at 1100 °C exhibited a homogeneous microstructure and a relative density of 97%, contributing to a large dielectric permittivity and elastic constant and yielding a thickness coupling factor k_t of ~30%. The electroacoustic response of the multilayer structure in water provides a centre frequency of 15 MHz and a very large fractional bandwidth (BW) of 127% at -6 dB. The multilayer structure is a candidate for imaging applications operating above 15 MHz, especially by realising focused-beam structure through lenses to further increase the sensitivity in the focal zone.

Screen Printed Copper and Tantalum Modified Potassium Sodium Niobate Thick Films on Platinized Alumina Substrates

We show how sintering in different atmospheres affects the structural, microstructural, and functional properties of ~30 μm thick films of K_0.5Na_0.5NbO₃ (KNN) modified with 0.38 mol% K_5.4Cu_1.3Ta₁₀O₂₉ and 1 mol% CuO. The films were screen printed on platinized alumina substrates and sintered at 1100 °C in oxygen or in air with or without the packing powder (PP). The films have a preferential crystallographic orientation of the monoclinic perovskite phase in the [100] and [-101] directions. Sintering in the presence of PP contributes to obtaining phase-pure films, which is not the case for the films sintered without any PP notwithstanding the sintering atmosphere. The latter group is characterized by a slightly finer grain size, from 0.1 μm to ~2 μm, and lower porosity, ~6% compared with ~13%. Using piezoresponse force microscopy (PFM) and electron backscatter diffraction (EBSD) analysis of oxygen-sintered films, we found that the perovskite grains are composed of multiple domains which are preferentially oriented. Thick films sintered in oxygen exhibit a piezoelectric d₃₃ coefficient of 64 pm/V and an effective thickness coupling coefficient k_t of 43%, as well as very low mechanical losses of less than 0.5%, making them promising candidates for lead-free piezoelectric energy harvesting applications.

Investigations of ferroelectric polycrystalline bulks and thick films using piezoresponse force microscopy

In recent years, ferroelectric/piezoelectric polycrystalline bulks and thick films have been extensively studied for different applications, such as sensors, actuators, transducers and caloric devices. In the majority of these applications, the electric field is applied to the working element in order to induce an electromechanical response, which is a complex phenomenon with several origins. Among them is the field-induced movement of domain walls, which is nowadays extensively studied using piezoresponse force microscopy (PFM), a technique derived from atomic force microscopy. PFM is based on the detection of the local converse piezoelectric effect in the sample; it is one of the most frequently applied methods for the characterization of the ferroelectric domain structure due to the simplicity of the sample preparation, its non-destructive nature and its relatively high imaging resolution. In this review, we focus on the PFM analysis of ferroelectric bulk ceramics and thick films. The core of the paper is divided into four sections: (i) introduction; (ii) the preparation of the samples prior to the PFM investigation; (iii) this is followed by reviews of the domain structures in polycrystalline bulks; and (iv) thick films.