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

Abstract

We show how sintering in different atmospheres affects the structural, microstructural, and functional properties of ~30 μm thick films of K0.5Na0.5NbO3 (KNN) modified with 0.38 mol% K5.4Cu1.3Ta10O29 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 kt 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.

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

“…The intensities of the (100) and (010) peaks at 2 Theta ~22 degrees and the intensities of the (−101), (101), and (110) peaks at 2 Theta ~32 degrees did not match the intensities for the bulk ceramics (Figure 6b,c). It has been reported that the KNN-based thick films on alumina have a preferential crystallographic orientation in the [100] and [−101] directions, which is related to the stresses developed in the thick films due to the mismatch between the thermal expansion of the KNN and the alumina substrate and the phase transition of the KNN [15,16,28]. Alumina has a thermal expansion coefficient (TEC) of 8 × 10 −6 K −1 , while the TEC of KNN is lower, namely, 7.5 × 10 −6 K −1 , 4.35 × 10 −6 K −1 , and 2.96 × 10 −6 K −1 for the cubic, tetragonal, and monoclinic phases, respectively [29].…”