Modification of strain and piezoelectricity in (K,Na)NbO3–(Bi,Na)HfO3 lead-free ceramics with high Curie temperature

Abstract

a b s t r a c tIn this work, the (1-x)K 0.45 Na 0.55 NbO 3 -xBi 0.5 Na 0.5 HfO 3 lead-free ceramics with a high Curie temperature were prepared by the normal sintering, and the enhancement in strain and piezoelectricity can be attained by tailoring the corresponding compositions. The orthorhombic-tetragonal (OeT) phase coexistence was observed in the ceramics with 0.03 < x < 0.055, and then such a phase boundary was reasonably identified by X-ray diffraction patterns as well as temperature -dependent Raman spectra and dielectric constant. A large piezoelectric constant (d 33 ) of~385 pC/N and a high Curie temperature (T C ) of 315 C can be simultaneously induced in the ceramics with x ¼ 0.05. More interestingly, a high unipolar strain of~0.187% was shown in the ceramics with x ¼ 0.04. It was found that the enhanced piezoelectric properties should be attributed to the two phase coexistence as well as enhanced dielectric and ferroelectric properties. We believe that this material is one of the most promising candidates in the field of high-temperature piezoelectrics.

Electrocaloric effect and pyroelectric performance in (K,Na)NbO3‐based lead‐free ceramics

“…However, the true evolution of phase structure is further confirmed via the measurement of phase transition temperature, which causes the abnormal variations of the dielectric constant (ε r ). [33][34][35][36][37][38][39] To investigate the effects of BNZ content on the Curie temperature (T C ), the T-ε r curves of the KNN-xBNZ ceramics are measured at 1, 10 and 100 kHz from 25°C to 400°C, as displayed in Figure 4A-D. Obviously, the composition dependence of phase structure for all ceramics is clearly observed in this work.…”

“…These results are in agreement with the previous works. [33][34][35][36][37][38][39] To investigate the effects of BNZ content on the Curie temperature (T C ), the T-ε r curves of the KNN-xBNZ ceramics are measured at 1, 10 and 100 kHz from 25°C to 400°C, as displayed in Figure 4A-D. The peak of phase transition from O phase to T phase, and the one from T phase to C phase can be clearly seen for x = 0.03 and x = 0.04 in Figure 4A,B, while only the single permittivity peak, corresponding to T C , is found for x = 0.05 and x = 0.06 in Figure 4C,D due to the R-T phase transition is suppressed.…”

Structural and piezoelectric properties of textured NLKNS‐CZ thick films and their application in planar piezoactuator

“…NKN‐related piezoceramics with the O‐R multi‐structure exhibited a relatively small d 33 value ranging between 200 pC/N and 260 pC/N 17–21 . However, NKN‐related piezoceramics with T‐O, T‐R, and T‐O‐R multi‐structures exhibited large d 33 values 6,22–25 . Specifically, a large d 33 of 650 ± 20 pC/N was observed from the NKN‐related piezoceramic with the T‐O‐R multi‐structure 26 …”

Properties and structures of nonstoichiometric (K, Na)NbO3‐based lead‐free ceramics

“…However, a pure KNN ceramic prepared by solid‐state reaction method is difficult to prepare dense samples and obtain good properties for the volatilization of alkalis at high temperature and narrow temperature range of sintering . In order to solve these problems to obtain well‐sintered and dense KNN ceramics with enhanced piezoelectric properties, some ways have been proposed and examined, such as ion substitutions, sintering aids, preparation methods and construction the phase boundaries near room temperature . And it is well‐known that a dramatic enhancement of piezoelectricity can be achieved through the construction of phase boundaries near room temperature, which become the hotspot in KNN‐based ceramics …”