Thermally stable piezoelectric properties of (K, Na)NbO3-based lead-free perovskite with rhombohedral-tetragonal coexisting phase

Section: Resultsmentioning

confidence: 99%

Simultaneously enhanced piezoelectric response and piezoelectric voltage coefficient in textured KNN‐based ceramics

Liu

Shen

et al. 2017

“…17 For KNN-based ceramics, the main Raman vibrations stem from the NbO 6 octahedron. 17 For KNN-based ceramics, the main Raman vibrations stem from the NbO 6 octahedron.…”

Section: Resultsmentioning

confidence: 99%

Structural evolution of the R‐T phase boundary in KNN‐based ceramics

Xiao

et al. 2017

Self Cite

Although a rhombohedral‐tetragonal (R‐T) phase boundary is known to substantially enhance the piezoelectric properties of potassium‐sodium niobate ceramics, the structural evolution of the R‐T phase boundary itself is still unclear. In this work, the structural evolution of R‐T phase boundary from −150°C to 200°C is investigated in (0.99−x)K0.5Na0.5Nb1−ySbyO3–0.01CaSnO3–xBi0.5K0.5HfO3 (where x = 0‐0.05 with y = 0.035, and y = 0‐0.07 with x = 0.03) ceramics. Through temperature‐dependent powder X‐ray diffraction (XRD) patterns and Raman spectra, the structural evolution was determined to be Rhombohedral (R, <−125°C)→Rhombohedral + Orthorhombic (R + O, −125°C to 0°C)→Rhombohedral + Tetragonal (R + T, 0 °C to 150°C)→dominating Tetragonal (T, 200°C to Curie temperature (TC)) → Cubic (C, >TC). In addition, the enhanced electrical properties (e.g., a direct piezoelectric coefficient (d33) of ~450 ± 5 pC/N, a conversion piezoelectric coefficient (d33∗) of ~580 ± 5 pm/V, an electromechanical coupling factor (kp) of ~0.50 ± 0.02, and TC~250°C), fatigue‐free behavior, and good thermal stability were exhibited by the ceramics possessing the R‐T phase boundary. This work improves understanding of the physical mechanism behind the R‐T phase boundary in KNN‐based ceramics and is an important step toward their adoption in practical applications.

“…[8][9][10][11][12] Normally, the high ECE can be achieved in the vicinity of the Curie temperature (T C ) or the polymorphic phase transition (PPT) region with different ferroelectric phases in ferroelectric materials due to the large entropy change. [14][15][16][17][18][19][20][21][22] Recently, some investigations on ECE are also reported in the field of KNN-based materials. By contrast, the PPT region with different ferroelectric phases can be easily obtained near ambient temperature, offering immense potential in practical applications.…”

Section: Introductionmentioning

confidence: 99%

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

Yang

Hao

2019

The issue of how to achieve an electrocaloric effect (ECE) and pyroelectric effect in a material simultaneously remains to be a challenge for developing practical solid‐state cooling devices and RF‐detectors. Here, we structure a polymorphic phase transition (PPT) region by doping modification in KNN‐based ceramics, which are developed to achieve the ECE. The direct measured ECE and pyroelectric properties are investigated in lead‐free (1‐x)K0.5Na0.5NbO3‐xBi0.5Na0.5ZrO3 (KNN‐xBNZ) ceramics. The adiabatic temperature change (∆T) of 0.22 K at 100°C, 0.14 K at 70°C and 0.16 K at 30°C can be obtained under an electric field of 35 kV cm–1 for x = 0.03, 0.04 and 0.05, respectively. In addition, the temperature dependence of pyroelectric coefficient (p) is established for all compositions via the Byer‐Roundy method. A large p of 454.46 × 10–4 C m–2 K–1 is detected at Curie temperature (TC) in the ceramics with x = 0.03. Achieving electrocaloric effect and pyroelectric performance simultaneously may shed light and provide a feasible design scheme for developing practically useful electrocaloric and pyroelectric materials.