Ultrahigh Piezoelectric Properties in Textured (K,Na)NbO 3 ‐Based Lead‐Free Ceramics

Particularly, unipolar strain and its temperature stability comparable to those of soft PZT-4 ceramics were reported in textured (K 0.44 Na 0.52 Li 0.04 )(Nb 0.84 Ta 0.10 Sb 0.06 )O 3 (LF4T) ceramics synthesized by the reactive template grain growth (RTGG) method. [6] Subsequent investigations focused on the improvement of both unipolar strain and its temperature stability using conventional sintering method due to high cost of RTGG. Vast studies strongly proved that phase boundary is an effective way to improve strain properties of KNN-based ceramics. [1] Particularly, the construction of new phase boundary by simultaneously shifting the rhombohedral-orthorhombic and orthorhombic-tetragonal phase transition temperature (e.g., T R-O and T O-T ) toward room temperature proved to enhance the piezoelectric properties of KNN-based ceramics. [1,7] Although the improved piezoelectricity can be guaranteed by means of phase boundaries, the related electrical properties still exhibited the strong temperature dependence due to the nature of polymorphic phase boundary that is different from the morphotropic phase boundary in PZT-based ceramics. [1,2,4,5] More importantly, the systematical investigations on how the phase boundaries affected the strain and its temperature stability is still missing, which could further promote the understanding of KNNbased ceramics.Recently, the temperature-insensitive dielectric properties were reported in SrZrO 3 -modified KNN-based ceramics, accompanying with small permittivity variation of ±15% (−65 to 201 °C). [8] Here, (0.99-x)(K 0.5 Na 0.5 )(Nb 0.965 Sb 0.035 )O 3 -0.01SrZrO 3 -x(Bi 0.5 Na 0.5 )ZrO 3 (x = 0-0.05) ceramics were chosen as an example to illustrate the effects of phase boundaries on the strain and its temperature stability. Through the study of temperature-dependent unipolar strain at different phase boundaries and similar phase boundary with different locations, effects of phase boundaries on strain and its temperature stability were illustrated. More importantly, the improved temperature stability of unipolar strain (S uni ) was observed in the ceramics (x = 0.03), e.g., high retention (≈95%) of S uni at T = 180 °C and low variation of 24% at T = 20-180 °C. The related physical mechanisms were discussed in detail. Results and DiscussionA typical perovskite structure without any other secondary phases was found in all samples ( Figure S1, Supporting Information).

Section: Wwwadvelectronicmatdesupporting

confidence: 80%

Section: Wwwadvelectronicmatdementioning

confidence: 68%

Section: Wwwadvelectronicmatdementioning

confidence: 99%

See 1 more Smart Citation

Modifying Temperature Stability of (K,Na)NbO₃ Ceramics through Phase Boundary

Xiao

et al. 2018

“…Figure 7a,b and Figure 7c,d show the high-magnification bright field TEM images of domain morphologies for 0.76-µm-sized and 3.31-µm-sized samples, respectively. [41] Therefore, the strip-like nanodomains can give rise to the enhanced piezoelectricity of the coarse-grained samples. Compared to fine-grained samples, typical strip-like nanodomains in the size range of 20-100 nm can be obviously observed in the coarse-grained sample, as presented in Figure 7c,d.…”

Section: Resultsmentioning

confidence: 99%

A Study on the Relationship Between Grain Size and Electrical Properties in (K,Na)NbO₃‐Based Lead‐Free Piezoelectric Ceramics

Yang

et al. 2019

Self Cite

The 0.5 wt% MnO2‐doped 0.95(K0.5Na0.5)(Nb0.965Sb0.035)O3‐0.01CaZrO3‐0.04(Bi0.5K0.5)(Hf0.98Ti0.02)O3 (95KNNS‐1CZ‐4BKHT) lead‐free ceramics with grain size from 0.31 to 3.83 µm are fabricated by hot‐press sintering (HPS), microwave sintering (MS), conventional sintering (CS), two‐step sintering (TSS), and a combination of two of the above‐mentioned methods. Then, the grain size effects on the phase transition, electrical properties, domain structure, and temperature stability of the ceramics are investigated. The phase structure evolves from single rhombohedral (R) phase to coexisted rhombohedral‐tetragonal (R‐T) phases around 1 µm. The electromechanical properties are strongly grain size dependent. The values of piezoelectric coefficient (d33) and planar electromechanical coupling factor (kp) first rise sharply when the grain size is less than 1 µm, and then increase mildly in the grain size range from 2.55 to 3.04 µm and finally almost remain a constant (≈450 pC N−1 and 54%) when the grain size is larger than 3.31 µm. The R‐T phase coexistence and strip‐like nanodomain structure characterized by an easier switching feature contribute to the high piezoelectric and electromechanical properties of coarse‐grained samples. This work not only clarifies the relationship between grain size and electrical properties in KNN‐based ceramics, but also provides a novel strategy for developing high‐performance lead‐free piezoceramics.

“…Subsequently, the direct observation of spontaneous polarization and its inversion under an external electric field was performed using the piezoresponse force microscopy (PFM). [23,24] The local ferroelectric loops were further investigated on the same α-In 2 Se 3 nanoflake and the results are shown in Figure 2e. First, the OOP spontaneous polarization switching behaviors were investigated using the high-resolution PFM ( Figure S4, Supporting Information).…”

Section: Ferroelectricity Characterizationsmentioning

confidence: 99%

Intrinsic Dipole Coupling in 2D van der Waals Ferroelectrics for Gate‐Controlled Switchable Rectifier

Dai

Wang

et al. 2019

OOP) and in-plane (IP) ferroelectricity could be easily achieved in some atomically thin vdWs 2D ferroelectric films, such as SnTe, CuInP 2 S 6 , LiAlTe 2 , and In 2 Se 3 . [8][9][10][11][12][13][14] Particularly, different from ultrathin SnTe and CuInP 2 S 6 , whose polarization only involves either pure IP or OOP orientations, atomically thin 2D In 2 Se 3 shows both IP and OOP ferroelectricity in its ground state of the α phase. [12] And the IP and OOP polarizations of 2D α-In 2 Se 3 have strong interrelated coupling. [15][16][17][18] In the previous work, we found that the OOP dipole in trilayer In 2 Se 3 is locked by the IP lattice asymmetry and its switching is related to the inversion of IP lattice orientation. [18] Up to date, there are few reports in the literature regarding ultimate miniature switchable rectifiers made of these atomically thin 2D ferroelectrics by utilizing the dipole polarization coupling. [19] Here, we report the fabrication of a gate-controlled switchable ferroelectric diode based on the single crystal of α-In 2 Se 3 by utilizing the interrelated coupling effect of OOP and IP polarizations (Figure 1). This ferroelectric diode can be inversed effectively by switching the gate bias between the negative (Figure 1a) and the positive configurations (Figure 1b). With a good rectification property of the ferroelectric diode, a switchable dynamic half-wave rectifier was realized. This kind of 2D ferroelectric diode has the advantages of simplicity in fabrication compatibility with complementary Miniaturization of device elements, such as ferroelectric diodes, depends on the downscaling of ferroelectric film, which is also crucial for developing high-density information storage technologies of ferroelectric random access memories (FeRAMs). Recently emerged ferroelectric two-dimensional (2D) van der Waals (vdWs) layered materials bring an additional opportunity to further increase the density of FeRAMs. A lateral, switchable rectifier is designed and fabricated based on atomically thin 2D α-In 2 Se 3 ferroelectric diodes, thus breaking the thickness limitation of conventional ferroelectric films and achieving an unprecedented level of miniaturization. This is realized through the interrelated coupling between out-of-plane and in-plane dipoles at room temperature; that is, horizontal polarization reversal can be effectively controlled through a vertical electric field. Being further explored as a switchable rectifier, the obtained maximum value of rectification ratio for the α-In 2 Se 3 based ferroelectric diode can reach up to 2.5 × 10 3 . These results indicate that 2D ferroelectric semiconductors can offer a pathway to develop next-generation multifunctional electronics. www.advelectronicmat.de metal-oxide-semiconductor (CMOS) technology, and superior electrical rectifying characteristics, showing great potential for future integrated electronic applications.