Effects of Na/K ratio on the phase structure and electrical properties of Na x K1−x NbO3 lead-free piezoelectric ceramics

Abstract

Lead-free piezoelectric Na x K 1-x NbO 3 (x = 0.3-0.8) (NKN) ceramics were fabricated by normal sintering at 1060°C for 2 h. Microstructures and electrical properties of the ceramics were investigated with a special emphasis on the influence of Na content. The grain size of the produced dense ceramic was decreased by increasing Na content. A discontinuous change in the space distance was found at the composition close to Na 0.7 K 0.3 NbO 3 ceramic, which indicates the presence of a transitional composition between two different orthorhombic phases, which is similar to the behavior of morphotropic phase boundary (MPB) in Na x K 1−x NbO 3 ceramics. Such MPB-like behavior contributes to the enhanced piezoelectric coefficient d 33 of 122 pC/N, planar-mode electromechanical coupling coefficient k P of 28.6%, and dielectric constant ε r of 703, respectively for the Na 0.7 K 0.3 NbO 3 ceramic. Cubic temperature T C and the transitional temperature T O-T from orthorhombic to tetragonal phase are observed at around 420°C and 200°C, respectively.

Effect of heat treatment on the microstructure and corrosion behaviour of Mg–Zn alloys

“…Electrochemical parameters of as‐cast in comparison with heat treated specimens are presented in Table . The corrosion rate ( P i ) of samples obtained from the corrosion current density was calculated according to the following equation . According to Equation , Mg–3Zn and heat treated alloys showed similar corrosion rate in the range of 4.81–5.21 mm/year.…”

“…However, Yang et al indicated that corrosion behaviour of binary Mg–Dy alloys were less significantly affected by heat treatment. Zhang et al also suggested that the corrosion rate of Mg–15Y alloy considerably increased after heat treatment. Studies on the effect of heat treatment on the corrosion resistance of AZ91D, Mg–Y and Mg–Dy alloys had been widely reported .…”

“…Zhang et al also suggested that the corrosion rate of Mg–15Y alloy considerably increased after heat treatment. Studies on the effect of heat treatment on the corrosion resistance of AZ91D, Mg–Y and Mg–Dy alloys had been widely reported . However there is hardly any study on the microstructures and degradation behaviour of Mg–Zn alloys under various solid solution treatments.…”

Composition dependence of phase structure and electrical properties in lead-free (1-x)(K0.42Na0.585)(Nb1−Sb )O3-xBi0.5K0.5ZrO3 piezoceramics

“…Previously, it was found that the K/Na ratio and the Na contents can also affect electrical performance of KNN -based materials [14,15]. Table 1 lists the relationships between piezoelectric properties and phase boundary of KNN -based ceramics [6,[9][10][11][12][13][14][15]. It shows that the piezoelectric properties of KNN -based materials strongly depend on the type of phase boundaries, and the rhombohedral-tetragonal (R-T) phase boundary plays a dominant role on their piezoelectricity.…”

Ferroelectric KNNT Fibers by Thermoplastic Extrusion Process: Microstructure and Electromechanical Characterization

“…The higher Na-K ratio in the 300-µm fibers seen from EDX and XRD resulted in samples with lower deformation, as suggested by Zhao et al [32], though unlike Zhao et al, the effect observed with the grain size resembled that of Zhang et al, whereby with an increasing Na-K ratio, the grain size decreased [39], and the effect on Pr was more related to the effect seen in Du et al, where an optimum ratio of 54:46 of Na-K was found, after which any increase in the ratio led to a decrease in the Pr [40]. The differing hypotheses from the various groups suggest that the results improve to a certain optimum where the greatest amount of phases exist, i.e., MPT, and then decrease, as was seen in Du et al, as the alkali content moves away from the MPT.…”