Linear Thermal Expansion of Lead-Free Piezoelectric K0.5Na0.5NbO3 Ceramics in a Wide Temperature Range

Abstract

The objective of this work was to examine linear thermal expansion of K 0.5 Na 0.5 NbO 3 ceramics between room temperature and 790°C by contact dilatometry. The material was single phase with 95.5% relative density and with a uniform microstructure. Three distinct regions of thermal expansion could be discerned, corresponding to the three phases of K 0.5 Na 0.5 NbO 3 : monoclinic (assuming a single perovskite unit cell), tetragonal, and cubic, separated by discontinuities as typical for the first-order phase transitions. The linear coefficient of thermal expansion between 30°and 195°C is 2.96 3 10 À6 K À1 , between 208°and 364°C is 4.35 3 10 À6 K À1 , and between 434°and 790°C is 7.52 3 10 À6 K À1 . †

Lead‐Free Ferroelectric Potassium Sodium Niobate Thin Films from Solution: Composition and Structure

“…As compared to the XRD pattern of the powder with the cell parameters a , b , c , and β 0.40046 nm, 0.39446 nm, 0.40020 nm, and 90.333°, respectively, the intensities of the (( h 00) + (00 l )) in relation to (0 k 0) are inversed, meaning that most of the unit cells in the 10K‐ and even more in the 10Na‐KNN thin films are b ‐axis‐oriented. The b ‐axis orientation is the consequence of the tensile stresses which develop in the film after heating, due to thermal expansion coefficient mismatch of the substrate and the thin film, which we relate to the considerably lower thermal expansion coefficient of silicon than that of KNN …”

Strain-Mediated Substrate Effect on the Dielectric and Ferroelectric Response of Potassium Sodium Niobate Thin Films

“…According to the supplier information, CTE of Pt/TiO 2 /SiO 2 /Si substrates is 2.3 × 10 −6 K −1 , while that of SrTiO 3 is 9 × 10 −6 K −1 . Comparing with the average CTE of 4.72 × 10 −6 K −1 reported for KNN [27], a tensile thermal stress of 252 MPa is expected to occur at RT in KNN films deposited on Si substrates at 750 • C, while a compressive thermal stress of −445 MPa should be induced on SrTiO 3 substrates. These values are also shown in Table 2, revealing a complete agreement with the measured residual stress values.…”

(K,Na)NbO3‐Based Lead‐Free Piezoceramics: Fundamental Aspects, Processing Technologies, and Remaining Challenges

“…As mentioned previously, the room‐temperature piezoelectric properties in KNN‐based ceramics can be largely improved by proper chemical modifications, which are actually due to the tetragonal–orthorhombic PPT point ( T O–T ) shifting downward from around 200°C toward room temperature, namely PPT effect. Although sharing similarities with MPB in terms of property enhancement due to two‐phase coexistence, the PPT effect cannot help but suffer from problems of temperature instability . For example, Zhang et al .…”