Xiangjian Wang

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.

Potassium–sodium niobate lead-free ceramics: modified strain as well as piezoelectricity

The obvious conflicts between large piezoelectricity and high strain could be solved by developing new phase boundaries in potassium–sodium niobate materials. Here, we have solved this problem by extensive experimental researches and induced a larger strain as well as a higher piezoelectricity in (K, Na)NbO3. Large converse piezoelectric coefficient (d*33 = 599–1553 pm V−1) and high strain (0.18–0.46%) were achieved, which are the highest values reported to date in potassium–sodium niobate, suggesting that such a system is a promising lead-free candidate for electromechanical actuator applications. In addition, high d33 values of 400–490 pC N−1 have also been attained in the ceramic due to its rhombohedral–tetragonal phase boundary, as well as its composition.

Strong Piezoelectricity in (1 – x)(K0.4Na0.6)(Nb0.96Sb0.04)O3-xBi0.5K0.5Zr1–ySnyO3 Lead-Free Binary System: Identification and Role of Multiphase Coexistence

Here we report a strong piezoelectric activity in (1 - x)(K0.4Na0.6)(Nb0.96Sb0.04)O3-xBi0.5K0.5Zr1-ySnyO3 lead-free ceramics by designing different phase boundaries. The phase boundaries concerning rhombohedral-orthorhombic-tetragonal (R-O-T) and rhombohedral-tetragonal (R-T) multiphase coexistence were attained by changing BKZS and Sn contents and then were identified by the X-ray diffraction patterns as well as temperature-dependent permittivity and ν1 Raman modes associated with BO6 perovskite octahedron. A high strain (strain = 0.21-0.28% and d33* = 707-880 pm/V) and a strong piezoelectric coefficient (d33 = 415-460 pC/N) were shown in the ceramics located at the multiphase coexistence region. The reported results of this work are superior to that (d33* ∼ 570 pm/V and d33 ∼ 416 pC/N) of the textured (K,Na,Li)(Nb,Ta,Sb)O3 ceramics [Nature 2004, 432, 84]. We believe that the material system of this work will become one of the most promising candidates for piezoelectric actuators.

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.

He+O2+H2O plasmas as a source of reactive oxygen species

The effect of water in the chemistry of atmospheric-pressure He+O2 plasmas is studied by means of a comprehensive global model. Water enables the generation of reactive oxygen species (ROS) cocktails that are rich not only in O, O2∗, and O3 but also in OH and H2O2. Due to its polar nature, water also leads to cluster formation, possibly affecting the plasma dynamics. Since the lifetime of many of the ROS is short, the plasma chemistry plays two roles: (i) direct interaction with superficial cells and (ii) triggering of a secondary chemistry that propagates the plasma treatment to regions away from the plasma-surface interface.

Role of antimony in the phase structure and electrical properties of potassium–sodium niobate lead-free ceramics

In the past ten years, antimony has been reported to strongly affect the developments in the piezoelectric properties of (K,Na)NbO3 (KNN) lead-free ceramics, that is, its enhanced piezoelectric activity is closely related to the doped antimony as well its content. In this work, we clarified the role of Sb5+ in the construction of a phase structure and the enhancement of electrical properties of a pure KNN ceramic. Research has shown that doping with Sb5+ can simultaneously move their orthorhombic–tetragonal phase transition temperature (TO–T) and rhombohedral–orthorhombic phase transition temperature (TR–O) forward to room temperature, benefiting the formation of three types of phase boundaries. The coexistence of rhombohedral and orthorhombic phases was established in the Sb5+ composition range of 0.07–0.09 by this regulation. In addition, their grain sizes were determined by the Sb5+ content, that is, the optimum Sb5+ content (x ≤ 0.05) induces grain growth, and their grain sizes become considerably smaller when the compositions deviate from x > 0.05. More importantly, their electrical properties could be also tuned by changing the Sb5+ content. Their dielectric, ferroelectric, and piezoelectric properties are strongly dependent on the antimony content, whereas the strain behavior is mainly ascribed to the multi-phase transition region as well as the structural change of phase transitions. As a result, this work would help to further understand the underlying physical origin for enhanced electrical properties in alkali niobate ceramics.

Composition-Driven Phase Boundary and Piezoelectricity in Potassium–Sodium Niobate-Based Ceramics

The piezoelectricity of (K,Na)NbO3 ceramics strongly depends on the phase boundary types as well as the doped compositions. Here, we systematically studied the relationships between the compositions and phase boundary types in (K,Na) (Nb,Sb)O3-Bi0.5Na0.5AO3 (KNNS-BNA, A=Hf, Zr, Ti, Sn) ceramics; then their piezoelectricity can be readily modified. Their phase boundary types are determined by the doped elements. A rhombohedral-tetragonal (R-T) phase boundary can be driven in the compositions range of 0.035≤BNH≤0.040 and 0.035≤BNZ≤0.045; an orthorhombic-tetragonal (O-T) phase boundary is formed in the composition range of 0.005≤BNT≤0.02; and a pure O phase can be only observed regardless of BNS content (≤0.01). In addition, the phase boundary types strongly affect their corresponding piezoelectricities. A larger d33 (∼440-450 pC/N) and a higher d33* (∼742-834 pm/V) can be attained in KNNS-BNA (A=Zr and Hf) ceramics due to the involvement of R-T phase boundary, and unfortunately KNNS-BNA (A=Sn and Ti) ceramics possess a relatively poor piezoelectricity (d33≤200 and d33*<600 pm/V) due to the involvement of other phase structures (O-T or O). In addition, the underlying physical mechanisms for the relationships between piezoelectricity and phase boundary types were also discussed. We believe that comprehensive research can design more excellent ceramic systems concerning potassium-sodium niobate.

New (1 − x)K0.45Na0.55Nb0.96Sb0.04O3-xBi0.5Na0.5HfO3 lead-free ceramics: Phase boundary and their electrical properties

Here, we reported a high unipolar strain and large piezoelectricity in new (1 − x)K0.45Na0.55Nb0.96Sb0.04O3-xBi0.5Na0.5HfO3 ceramics. The rhombohedral-tetragonal (R-T) phase boundary was constructed in the ceramics with 0.03 < x ≤ 0.05, which shows a large d33 value of ∼419 pC/N. More importantly, a high unipolar strain of ∼0.31% was observed due to the multiphase coexistence. In addition, the piezoelectricity of the ceramics could be effectively enhanced if their compositions are located at the phase boundaries region, where a very low electric field of ∼1.2 kV/mm can readily rotate the R/T domains. We also noticed that the deviation from phase boundary induced by applying an external electric field results in the deterioration of piezoelectricity after the “second-poling” method. We believe that as a potassium-sodium-niobate based material, the ceramics developed in this work may find practical applications in lead-free piezoelectric devices such as actuators and fuel injectors in the future owing to th...

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.