Environment protection and human health concern is the driving force to eliminate the lead from commercial piezoelectric materials. In 2004, Saito et al. [ Saito et al., Nature , 2004 , 432 , 84 . ] developed an alkali niobate-based perovskite solid solution with a peak piezoelectric constant d33 of 416 pC/N when prepared in the textured polycrystalline form, intriguing the enthusiasm of developing high-performance lead-free piezoceramics. Although much attention has been paid on the alkali niobate-based system in the past ten years, no significant breakthrough in its d33 has yet been attained. Here, we report an alkali niobate-based lead-free piezoceramic with the largest d33 of ∼490 pC/N ever reported so far using conventional solid-state method. In addition, this material system also exhibits excellent integrated performance with d33∼390-490 pC/N and TC∼217-304 °C by optimizing the compositions. This giant d33 of the alkali niobate-based lead-free piezoceramics is ascribed to not only the construction of a new rhombohedral-tetragonal phase boundary but also enhanced dielectric and ferroelectric properties. Our finding may pave the way for "lead-free at last".

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.

The appearance of colossal permittivity (CP) materials broadens the choice of materials for energy-storage applications. Here we report colossal permittivity in ceramics of TiO 2 co-doped with niobium and trivalent cation {i.e., (A 0.5 Nb 0.5 ) x Ti 1Àx O 2 , A ¼ Bi, Pr, Dy, Sm, Gd, Yb, Ga, Al or Sc}, in particular in the (Bi 0.5 Nb 0.5 ) x Ti 1Àx O 2 ceramic system that was selected as a candidate material. A very large dielectric constant (3 r $ 4.2 Â 10 4 ) and a low dielectric loss (tan d $ 8.3%) were observed for (Bi 0.5 Nb 0.5 ) x Ti 1Àx O 2 ceramics when measured at 1 kHz. Moreover, the addition of Bi and Nb can enhance the temperature stability (between À125-200 C) and frequency stability (between 10 2 to 10 6 Hz) of 3 r and tan d. The electron-pinned defect-dipoles are considered to be responsible for both their high 3 r and low tan d, which is consistent with changes of valence states determined by X-ray photoelectron spectroscopy. We believe that the TiO 2 ceramics as a CP material constitute one of the most promising candidates for high-energydensity storage applications.

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

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 < x < 0.05. For such composition, the ceramics show giant d33 of ∼380 pC/N, high Tc of ∼290 °C, and a good thermal-depolarization behavior (d33 > 300 pC/N) of ∼210 °C. We believe that the (1−x)KNNS-xBNKLZ system is very promising for lead-free piezoelectric applications.