This is a repository copy of Spark plasma texturing: A strategy to enhance the electromechanical properties of lead-free potassium sodium niobate ceramics.

reported by Shiraishi et al.,13,14 and 4 to 6 mm thick lms have good ferroelectric and piezoelectric properties (d 33 ¼ 68 pm V À1 ). Lusiola et al. reported the fabrication of NaNbO 3 -K 0.5 Na 0.5 NbO 3 (NN-KNN) thick lms using a low temperature molten salt powder synthesis combined with a hybrid powder/sol gel ink lm.15 These lms have a piezoelectric coefficient and relative permittivity around 18 pC N À1 and 250 to 800 (depending on the poling conditions), respectively. However, with chemical solution deposition methods, a repeated number of depositions are required to achieve a thick layer, increasing drastically the amount of defects in the nal lm, besides being a lengthy and costly process. Of all techniques for the fabrication of thick lms, electrophoretic deposition (EPD) stands out due its high exibility, low cost and simplicity of application. 23 Although that paper proves the feasibility of getting KNN thick lms by EPD, processing studies, dielectric characterization and relations between processing conditions and properties have not been reported.Within this context, in the present work K 0.5 Na 0.5 NbO 3 (KNN) thick lms are deposited on Pt foils by EPD and sintered at 1100 C for 2 h. We investigate the key parameters, and establish the relationships between suspension media, EPD process conditions, microstructure of the deposits, and resulting electrical properties of KNN lms. This work is also a part of a wide ranging study on the EPD processing of electroceramics that we have been carrying out. The use of EPD is well documented in the area of solid-state fuel cells and biomaterials. 16However, improved knowledge of EPD for dielectrics, piezoelectrics, ferroelectrics and related materials is still required. In our previous papers we have reported EPD of different electroceramic systems: piezoelectrics such as PZT, incipient ferroelectrics such as SrTiO 3 , low loss dielectrics such as BNT, and more recently low sintering temperature such as Tellurium based compounds. 19 22 Among these results, we demonstrated that the selection of the medium, the stability of the suspensions, and the control of the particle zeta potentials, critical for a good deposition, need to be established for each new electroceramic material being processed by EPD. The current study on KNN thick lms has not been reported before, and it is of interest for the fabrication of KNN thick lms and exploitation of KNN assets for the electroceramics community. ExperimentalK 0.5 Na 0.5 NbO 3 (KNN) powders were synthesised by a solid-state reaction method starting from Na 2 CO 3 (Chempur, purity 99.5%), K 2 CO 3 (Merck, purity 99.0%) and Nb 2 O 5 (BDH Chemicals, purity 99.5%). Due to their hygroscopic nature, the carbonates Na 2 CO 3 and K 2 CO 3 were heated to 150 C immediately prior to weighing. The powders were weighed according to the 1 : 1 : 2 stoichiometry, and ball milled in Teon jars containing absolute ethanol as a media and zirconia balls. The ball milling was performed for 5 h at 200 rpm. Aer drying the stoich...

A current challenge for the fabrication of functional oxide-based devices is related with the need of environmental and sustainable materials and processes. By considering both lead-free ferroelectrics of potassium sodium niobate (K0.5Na0.5NbO3, KNN) and aqueous-based electrophoretic deposition here we demonstrate that an eco-friendly aqueous solution-based process can be used to produce KNN thick coatings with improved electromechanical performance. KNN thick films on platinum substrates with thickness varying between 10 and 15 μm have a dielectric permittivity of 495, dielectric losses of 0.08 at 1 MHz, and a piezoelectric coefficient d33 of ∼70 pC/N. At TC these films display a relative permittivity of 2166 and loss tangent of 0.11 at 1 MHz. A comparison of the physical properties between these films and their bulk ceramics counterparts demonstrates the impact of the aqueous-based electrophoretic deposition (EPD) technique for the preparation of lead-free ferroelectric thick films. This opens the door to the possible development of high-performance, lead-free piezoelectric thick films by a sustainable low-cost process, expanding the applicability of lead-free piezoelectrics.

Direct ink writing (DIW) has become a widespread additive manufacturing technique for material engineering, but its application in lead‐free Ba0.85Ca0.15Zr0.1Ti0.9O3 piezoelectric ceramics from aqueous systems has not been reported so far to our knowledge. The main obstacle is the high extent of hydrolysis reactions undergone by the starting powders when dispersed in water, hindering the attainment of stable water‐based colloidal suspensions. This paper reports on the preparation of stable aqueous inks from a deagglomerated and surface‐treated powder synthesized by solid‐state reaction and on DIW of macroporous lead‐free piezoelectrics. Based on zeta potential and rheological measurements, the optimal amounts of processing additives (dispersant, binder, and coagulating agent) were selected to transform the initial fluid suspension to a viscoelastic paste with sufficient stiffness and stability for the printing process. Dielectric and piezoelectric properties of samples sintered under different temperatures were also investigated.

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