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 Teon jars containing absolute ethanol as a media and zirconia balls. The ball milling was performed for 5 h at 200 rpm. Aer drying the stoich...
