Xiaojing Cheng

Lead-free Piezoelectrics Based on Potassium–Sodium Niobate with Giant d33

High-performance lead-free piezoelectrics (d33 > 400 pC/N) based on 0.96(K0.5Na0.5)0.95Li0.05Nb1-xSbxO3-0.04BaZrO3 with the rhombohedral-tetragonal (R-T) phase boundary have been designed and prepared. The R-T phase boundary lies the composition range of 0.04 ≤ x ≤ 0.07, and the dielectric and piezoelectric properties of the ceramics with the compositions near the phase boundary are significantly enhanced. In addition, the ceramic with x = 0.07 has a giant d33 of ~425 pC/N, which is comparable to that (~416 pC/N) of textured KNN-based ceramics (Saito, Y.; Takao, H.; Tani, T.; Nonoyama, T.; Takatori, K.; Homma, T.; Nagaya, T.; Nakamura, M. Nature 2004, 432, 84). The underlying physical mechanisms for enhanced piezoelectric properties are addressed. We believe that the material system is the most promising lead-free piezoelectric candidates for the practical applications.

Giant d33 in (K,Na)(Nb,Sb)O3-(Bi,Na,K, Li)ZrO3 based lead-free piezoelectrics with high Tc

In this work, a lead-free piezoelectric system based on (1−x)(K0.48Na0.52)(Nb0.95Sb0.05)O3-xBi0.5(Na0.7K0.2Li0.1)0.5ZrO3 [(1−x)KNNS-xBNKLZ] is developed, and a rhombohedral-tetragonal phase boundary is constructed in this system. The relationship between the phase boundary and the piezoelectric properties of the (1−x)KNNS-xBNKLZ ceramics is illuminated. The coexistence of a tetragonal phase and a rhombohedral phase is identified in the composition range of 0.03   300 pC/N) of ∼210 °C. We believe that the (1−x)KNNS-xBNKLZ system is very promising for lead-free piezoelectric applications.

Colossal permittivity in ceramics of TiO2 Co-doped with niobium and trivalent cation

The appearance of colossal permittivity (CP) materials broadens the choice of materials for energy-storage applications. Here we report colossal permittivity in ceramics of TiO2 co-doped with niobium and trivalent cation {i.e., (A0.5Nb0.5)xTi1−xO2, A = Bi, Pr, Dy, Sm, Gd, Yb, Ga, Al or Sc}, in particular in the (Bi0.5Nb0.5)xTi1−xO2 ceramic system that was selected as a candidate material. A very large dielectric constant (er ∼ 4.2 × 104) and a low dielectric loss (tan δ ∼ 8.3%) were observed for (Bi0.5Nb0.5)xTi1−xO2 ceramics when measured at 1 kHz. Moreover, the addition of Bi and Nb can enhance the temperature stability (between −125–200 °C) and frequency stability (between 102 to 106 Hz) of er and tan δ. The electron-pinned defect-dipoles are considered to be responsible for both their high er and low tan δ, which is consistent with changes of valence states determined by X-ray photoelectron spectroscopy. We believe that the TiO2 ceramics as a CP material constitute one of the most promising candidates for high-energy-density storage applications.

Large d33 in (K,Na)(Nb,Ta,Sb)O3-(Bi,Na,K)ZrO3 lead-free ceramics

To protect the environment and human health, it is necessary to develop high-performance lead-free piezoceramics to replace the lead-based ones in some electronic devices. Here we report first a large piezoelectricity in (K,Na)NbO3-based lead-free piezoceramics prepared by the conventional solid-state method. The rhombohedral–tetragonal phase boundary is observed in the ceramics with a composition of 0.04 ≤ x ≤ 0.06. Those ceramics with 0.01 ≤ x ≤ 0.06 possess a good comprehensive performance of d33 (380–460 pC N−1) and TC (170–287 °C). Moreover importantly, a peak d33 of ∼460 pC N−1 is shown in the ceramic with x = 0.04, which is superior to all other reported results of KNN-based ceramics, including the reported results by Saito et al. (Nature, 2004, 432, 84). We believe that such a material system is a very promising candidate for potassium–sodium niobate piezoceramics.

New Potassium–Sodium Niobate Ceramics with a Giant d33

For potassium-sodium niobate, poor piezoelectric properties always perplex most researchers, and then it becomes important to attain a giant piezoelectricity. Here we reported a giant piezoelectric constant in (1-x)(K0.48Na0.52)(Nb0.95Sb0.05)O3-xBi0.5Ag0.5ZrO3 lead-free ceramics. The rhombohedral-tetragonal phase boundary was shown in the ceramics with 0.04<x≤0.05, and then the ceramic with x=0.0425 possesses a giant d33 of ∼490 pC/N. We also discussed the physical mechanisms of enhanced piezoelectricity. As a result, such a research can benefit the sustainable development of (K,Na)NbO3 materials.

Mediating the contradiction of d33 and TC in potassium-sodium niobate lead-free piezoceramics.

For potassium-sodium niobate, the piezoelectric constant (d33) was usually improved by sacrificing the Curie temperature (TC). In this work, a material system of 0.992(K0.46Na0.54)0.965Li0.035Nb(1-x)Sb(x)O3-0.008BiScO3 has been designed and prepared with the aim of achieving both a large d33 and a high TC at the same time. The chemical compositions are found to be homogeneously distributed in the ceramics. The introduction of Sc is found to be responsible for different grain sizes. The rhombohedral-tetragonal phase coexistence zone lies in the composition range of 0.02<x ≤ 0.06. The ceramic is thermally stable in terms of ferroelectric properties. The change in the domain-wall activities induced by the configuration variation of defect dipoles upon annealing is believed to be responsible for the variation in the d33 at different temperatures. The ceramic with x = 0.025 shows a good comprehensive performance of d33 ≈ 325 pC/N and k(p) ≈ 48%, together with a high T(C) of ~358 °C, demonstrating that this material system is a promising candidate for high-temperature piezoelectric applications.

New potassium-sodium niobate lead-free piezoceramic: Giant-d33 vs. sintering temperature

The objective of this work is to achieve a giant piezoelectric constant in (K,Na)NbO3-based lead-free ceramics, and then 0.96K0.46Na0.54Nb0.95Sb0.05O3-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 lead-free piezoceramics were designed and prepared by optimizing the sintering temperature (TS). The rhombohedral-tetragonal phase boundary is found in the ceramics sintered at 1070 ∼ 1105 °C and is suppressed when sintered at low TS of 1060 ∼ 1065 °C. The threshold for TS is 1070 °C in terms of their ferroelectric and piezoelectric properties owing to the difference in the phase boundary and the microstructure, and a large d33 of 388 ∼ 465 pC/N could be attained in a wide TS range of 1070 ∼ 1105 °C, benefiting their practical applications because of broad TS. More interestingly, the ceramic sintered at 1075 °C has a giant d33 of ∼465 pC/N. We think that such a giant d33 of this material system can benefit the development of (K,Na)NbO3-based piezoceramics.

Rhombohedral–tetragonal phase boundary and electrical properties of new K0.48Na0.52Nb0.98Sb0.02O3-Bi0.5Na0.5ZrO3 lead-free piezoceramics

(1 − x)K0.48Na0.52Nb0.98Sb0.02O3-xBi0.5Na0.5ZrO3 lead-free piezoceramics were prepared by using the conventional solid-state method. In this material system, (Bi0.5Na0.5)2+ and Zr4+ can decrease the orthorhombic-tetragonal phase temperature and increase the rhombohedral–orthorhombic phase temperature. The rhombohedral–tetragonal phase coexistence is identified in the ceramics with the compositional range of 0.03 < x < 0.05. The ceramic with x = 0.04 has an enhanced piezoelectric behaviour of d33 ~ 257 pC N−1 and kp ~ 41%, which is three times higher than that of a pure KNN ceramic. In addition, the enhanced stability of piezoelectric and ferroelectric properties is also observed in such a ceramic. These results show that such a new lead-free material system is a promising candidate for piezoelectric devices.

Lead-free piezoelectric ceramics based on (0.97 − x)K0.48Na0.52NbO3-0.03Bi0.5(Na0.7K0.2Li0.1)0.5ZrO3-xB0.5Na0.5TiO3 ternary system

In this work, the ternary system of potassium-sodium niobate has been designed to enhance the piezoelectric properties without sacrificing the Curie temperature greatly, and (0.97 − x)K0.48Na0.52NbO3-0.03Bi0.5(Na0.7K0.2Li0.1)0.5ZrO3-xB0.5Na0.5TiO3 ceramics have been prepared by the conventional solid-state method. The effect of B0.5Na0.5TiO3 content on the microstructure and electrical properties of the ceramics is studied. The phase diagram shows a phase boundary of the rhombohedral-tetragonal (R-T) phase coexistence in the composition range of 0.5% < x < 1.5%, and then an enhanced dielectric, ferroelectric, and piezoelectric behavior is obtained at such a phase boundary zone. The ceramic with x = 0.01 has an optimum electrical behavior of d33 ∼ 285 pC/N, kp ∼ 0.40, er ∼ 1235, tan δ ∼ 0.031, Pr ∼ 14.9 μC/cm2, and Ec ∼ 15.2 kV/cm, together with a high Curie temperature of ∼347 °C. The large d33 in such a ternary system is due to a composition-induced R-T phase transition and a higher ɛrPr, and the thermal...