X.G. Tang

Electromechanical and ferroelectric properties of (Bi1∕2Na1∕2)TiO3–(Bi1∕2K1∕2)TiO3–BaTiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (0.95−x)(Bi1∕2Na1∕2)TiO3–x(Bi1∕2K1∕2)TiO3–0.05BaTiO3 (abbreviated as BNT–BKT–BT100x, with x ranged from 0 to 20mol%) have been studied. Effects of amount of BKT on the electrical properties and crystal structure were examined. BNT–BKT–BT5 ceramics give good performances with piezoelectric constant d33=148pC∕N, electromechanical coupling factor kp=34%, kt=49.2%, free permittivity e33T∕e0=700, and dissipation factor tanδ=2% at 1kHz. Accordingly, the sample shows larger remanent polarization and lower coercive field than 0.95BNT–0.05BT ceramics. X-ray diffraction analysis shows that incorporated BKT diffuses into the BNT–BT lattice to form a solid solution during sintering, but changes the crystal structure from rhombohedral to tetragonal symmetry at higher BKT amounts.

Synthesis and piezoresponse of highly ordered Pb(Zr0.53Ti0.47)O3 nanowire arrays

We report the synthesis and characterization of ferroelectric lead zirconate titanate PbsZr0.53Ti0.47dO3 (PZT) nanowires. The PZT nanowires, with diameters of about 45 nm and lengths of about 6 mm, were fabricated by means of a sol-gel method utilizing nanochannel alumina templates. After postannealing at 700 ° C, the PZT nanowires exhibit a polycrystalline microstructure, and x-ray diffraction and transmission electron microscopy study revealed their perovskite crystal structure. The piezoelectric characteristics of individual PZT nanowires were demonstrated by piezoresponse force microscopy.

Effect of grain size on the electrical properties of (Ba,Ca)(Zr,Ti)O3 relaxor ferroelectric ceramics

(Ba0.90Ca0.10)(Zr0.25Ti0.75)O3 (BCZT) relaxor ferroelectric ceramics with grain sizes of 0.85, 2.5, 15, and 30μm were prepared from powders synthesized using a sol-gel process. The effects of grain size and dc field on the dielectric properties and tunabilities of BCZT ceramics were investigated. As the grain size decreased, the maximum dielectric constant decreased and the transition temperature increased. The BCZT ceramics with various grain sizes showed a typical relaxor ferroelectric behavior. The dielectric relaxation rate follows the Vogel–Fulcher relation. The dielectric constant is greatly suppressed and the low loss is obtained under a dc electric field. At room temperature (300K) and 20kV∕cm, the tunabilities and figures of merit are 42% and 62, 51% and 98, 56% and 193, and 51% and 182, respectively, for the BCZT ceramics with grain sizes of 0.85, 2.5, 15, and 30μm.

Dielectric behavior and microstructure of (Bi1∕2Na1∕2)TiO3–(Bi1∕2K1∕2)TiO3–BaTiO3 lead-free piezoelectric ceramics

(0.95−x)(Bi1∕2Na1∕2)TiO3–x(Bi1∕2K1∕2)TiO3–0.05BaTiO3 lead-free piezoelectric ceramics (abbreviated as BNT–BKT–BT100x with x varying from 0 to 20 mol %) are prepared by a solid-state reaction process. Variation of the dielectric properties and microstructure of BNT–BKT–BT100x ceramics with BKT content is studied. The results indicate that the relative permittivity er and loss tangent tanδ vary with the BKT amount. Scanning electron microscope observation also indicates that BKT in high amount affects the microstructure. X-ray diffraction analysis shows that the incorporated BKT diffuses into the BNT–BT lattice to form a solid solution during sintering.

Dielectric tunability of (Ba0.90Ca0.10)(Ti0.75Zr0.25)O3 ceramics

We have performed a study on the dielectric properties of (Ba0.90Ca0.10)(Ti0.75Zr0.25)O3 bulk ceramics prepared by a sol–gel technique in the cooling temperature range from 400to213K. The ceramics are found to exhibit an interesting dielectric response under the presence of a dc bias field. The field dependence of dielectric constant is stronger at T≈Tm (Tm is the temperature of dielectric maximum) and the field-induced variation of dielectric constant Δe is nonzero for T−Tm<150K. One striking feature of these ceramics is that they possess a broad optimum value of figure of merit (as high as 200 at 30kV∕cm) between the temperature range from 295 and 330K. At room temperature, the high tunability (K=60%), low-loss tangent (≈0.003), and large figure of merit (200), clearly indicate that these ceramics are suitable candidates for microwave applications.

Dielectric relaxation and electrical properties of 0.94Pb(Fe1∕2Nb1∕2)O3–0.06PbTiO3 single crystals

Dielectric response and electrical conduction properties of 0.94Pb(Fe1∕2Nb1∕2)O3–0.06PbTiO3 single crystals grown by the Bridgman method were studied. It was found that the single crystals did not show any sign of the presence of Curie temperature between room temperature and 300 °C. However, they exhibited very high dielectric constant at a frequency lower than 100 kHz, in the order of 105. Relaxation occurred at higher frequencies with a large decrease in dielectric constant, to about 1500. The thermal activation energy for relaxation was found to be ∼0.17eV, which is quite close to that for ac conductivity. It followed that the relaxation was attributed to the carriers hopping conduction, which is related to the possible jump motion of additional 3d electron between the equivalent positions of Fe ions.

Effect of CaRuO3 interlayer on the dielectric properties of Ba(Zr,Ti)O3 thin films prepared by pulsed laser deposition

Ba(Zr0.2Ti0.8)O3 (BZT) thin films on Pt(111)∕Ti∕SiO2∕Si(100) substrates without and with CaRuO3 (CRO) buffer layer were fabricated at 650°C in situ by pulsed laser deposition. The BZT thin films showed a dense morphology, many clusters are found on the surface images of BZT/Pt films, which are composed by nanosized grains of 25–35nm; the average grain size of BZT/CRO films is about 80nm, which lager than that of BZT/Pt thin film. The dielectric constants and dissipation factors of BZT/Pt and BZT/CRO thin films were 392 and 0.019 and 479 and 0.021 at 1MHz, respectively. The dielectric constant of BZT/Pt and BZT/CRO thin films changes significantly with applied dc bias field and has high tunabilities and figures of merit of ∼70% and 37 and 75% and 36, respectively, under an applied field of 400kV∕cm. The possible microstructural background responsible for the high dielectric constant and tunability was discussed.

Leakage current and relaxation characteristics of highly (111)-oriented lead calcium titanate thin films

Highly (111)-oriented (Pb0.76Ca0.24)TiO3 (PCT) thin films were grown on Pt/Ti/SiO2/Si substrates by a sol–gel process. The Au/PCT/Pt metal–insulator–metal film capacitor showed well-saturated hysteresis loops at an applied field of 800 kV/cm with remanent polarization (Pr) and coercive electric field (Ec) values of 18.2 μC/cm2 and 210 kV/cm, respectively. The leakage current depended on the voltage polarity. At low electrical field and with Pt electrode biased negatively, the Pt/PCT interface exhibits a Schottky emission characteristics. The Au/PCT interface forms an ohmic contact. The conduction current when the Au electrode is biased negatively shows a space-charge-limited behavior. The dielectric relaxation current behavior of Au/PCT/Pt capacitor obeys the well-known Curie–von Schweidler law at low electric field. At higher fields, the currents have contributions to both dielectric relaxation current and leakage current.

Effects of Ca doping on the Curie temperature, structural, dielectric, and elastic properties of Ba0.4Sr0.6−xCaxTiO3 (0⩽x⩽0.3) perovskites

The effects of Ca doping on the Curie temperature, structural, dielectric, and elastic properties of Ba0.4Sr0.6−xCaxTiO3 (0⩽x⩽0.3) has been studied. Powder x-ray diffraction revealed that the cubic lattice constant a decreases linearly with increasing x from 0 to 0.15, while showing an anomalous expansion between x=0.15 and x=0.18. This, together with the anomalies in the dielectric constants, Curie temperature TC, and elastic constants observed for 0.15 0.15, TC increases persistently up to x=0.25 and thereafter shows a decrease. These variations of TC with x have been interpreted in terms of Ca-doping-induced A-site cation size variance, a substitution of a small amount of Ca ions for Ti ions, and structural phase separation. Upon cooling the longitudinal elastic constant CL shows drastic sof...

Dielectric properties of (100)-oriented Ba(Zr, Ti)O3/La0.7Ca0.3MnO3 heterostructure thin films prepared by pulsed laser deposition

Highly (100)-oriented Ba(Zr0.2Ti0.8)O3/La0.7Ca0.3MnO3 (BZT/LCMO) heterostructure thin films have been grown on Si(100) and Pt(111)/Ti/SiO2/Si(100) substrates prepared by pulsed laser deposition. The structure and surface morphology of the films have been characterized by x-ray diffraction and atomic force microscopy. The dielectric constant of the films changes significantly with applied dc bias field and the films have high tuneability of 59.1%, 52% and 59.4% at an applied field of 400 kV cm−1, respectively, for the BZT film on Pt/Ti/SiO2/Si and the BZT/LCMO heterostructure films on Si and Pt/Ti/SiO2/Si substrates. The tuneability of the BZT/LCMO thin films on Pt-coated Si substrate was higher than that of the BZT thin films on Pt/Ti/SiO2/Si and LCMO/Si substrates. The high tuneability has been attributed to the (100) texture of the films and larger grain sizes. The BZT thin film is an attractive candidate for tuneable microwave device applications.