Xianlin Dong

Thermal depoling of high Curie point Aurivillius phase ferroelectric ceramics

The thermal depoling behavior of several different Aurivillius phase ferroelectric ceramics has been studied. This includes two-layer (CaBi2Nb2O9,Ca0.9Ba0.1Bi2Nb2O9,Bi3NbTiO9,Bi3Nb1.2Ti0.8O9), three-layer (Bi4Ti3O12), and four-layer [CaBi4Ti4O15,Ca0.94(Na,Ce)0.03Bi4Ti4O15] compounds. All of them have a high Curie point (Tc⩾675°C). The orthorhombic structured materials show good resistance to thermal depoling up to temperatures close to their Curie points. However, Bi4Ti3O12, which has a monoclinic structure, shows a significant reduction in d33 well before its Curie point. The monoclinic distortion produces more non-180° ferroelectric domain structures, and it is the thermal instability of these that accounts for their thermal depoling behaviour. Excess Nb doping of Bi3NbTiO9 produces a significant reduction in its resistance to thermal depoling, suggesting that the doping produces a lowering of the crystallographic symmetry.

Dielectric properties of Ba0.6Sr0.4TiO3∕Mg2SiO4∕MgO composite ceramics

The dielectric properties of BSTO∕Mg2SiO4∕MgO composite ceramics have been investigated systematically. The dielectric properties of BSTO composites under a dc bias field can be interpreted by the “soft-mode” theory near the phase transition and Johnson’s phenomenological equation far above the transition temperature. Compared with most of the other BSTO composite ceramics, BSTO∕Mg2SiO4∕MgO not only can be sintered at a lower temperature but also keep a higher dielectric tunability versus a lower dielectric constant. For example, BSTO∕35wt.%Mg2SiO4∕15wt.%MgO has a dielectric tunability ∼13.18% (under 2kV∕mm biasing) versus a dielectric constant er(0)∼118.40 at 25°C. It suggests that the dielectric properties are influenced to a great extent by the microstructure, and the dielectric tunability is enhanced when more continuous BSTO phase is obtained.

Wake-up effects in Si-doped hafnium oxide ferroelectric thin films

Hafnium oxide based ferroelectric thin films have shown potential as a promising alternative material for non-volatile memory applications. This work reports the switching stability of a Si-doped HfO2 film under bipolar pulsed-field operation. High field cycling causes a “wake-up” in virgin “pinched” polarization hysteresis loops, demonstrated by an enhancement in remanent polarization and a shift of negative coercive voltage. The rate of wake-up is accelerated by either reducing the frequency or increasing the amplitude of the cycling field. We suggest de-pinning of domains due to reduction of the defect concentration at bottom electrode interface as origin of the wake-up.

Charge-discharge properties of lead zirconate stannate titanate ceramics

The charge-discharge properties of lanthanum- and niobium-doped lead zirconate stannate titanate ceramics were investigated by directly measuring the hysteresis loops, dielectric constants under a dc bias field, and pulse discharge current-time curves after varying charge-discharge circulations. It was found that there was no significant effect of the charge-discharge circulation on these properties. The first pulse current peak reached 1.8 kA at 40 kV/cm, and most of the stored charge was released in 500 ns. These results show that the obtained slanted ceramics with high energy density can withstand hundreds of charge-discharge circulations and are very promising for pulse capacitor applications.

Temperature-dependent stability of energy storage properties of Pb0.97La0.02(Zr0.58Sn0.335Ti0.085)O3 antiferroelectric ceramics for pulse power capacitors

The dielectric properties and electrical hysteresis behaviors of Pb0.97La0.02(Zr0.58Sn0.335Ti0.085)O3 antiferroelectric (AFE) ceramics were investigated in this work with an emphasis on energy storage properties. Three phase transition points can be detected as temperature increases. AFE and paraelectric phases are found to coexist from 100 °C to 170 °C. The room temperature recoverable energy density is 1.37 J/cm3 at 8.6 kV/mm. With increasing temperature (from 20 °C to 100 °C) and frequency (from 0.01 to 100 Hz) under 8.6 kV/mm, the variation of recoverable energy density was less than 15%, all higher than 1.2 J/cm3. All the corresponding energy efficiencies were no less than 75%. The high energy density, high energy efficiency, and their weak dependence on temperature and frequency during a wide scope indicate that these antiferroelectric ceramics are quite promising to be used for pulse power capacitors applications.

Doping effects on the electrical conductivity of bismuth layered Bi3TiNbO9-based ceramics

Single phase Bi3TiNbO9 (BTNO)-based ceramics, with Sr2+ replacing Bi3+ as an acceptor dopant and Nb5+ and W6+ replacing Ti4+ as donor dopants, were prepared by conventional solid-state reaction method. The conductivity increased with acceptor dopant and decreased with donor dopant. These results indicate that the dominant conduction mechanism of pure BTNO is p type at low temperature range. Detailed investigations about the W6+ donor doped BTNO ceramics showed that when the doping amount x>0.01, the conductivity increases with increasing donor doping amount, suggesting that the extrinsic conductivity changes from p type to n type at the low temperature region. The extrinsic conductivity range extends to higher temperature with the increase of donor doping amount. At high temperature range the intrinsic electrical conductivity activation energy is about 1.8eV. This value is equal to half the band gap energy.

Reversible pyroelectric response in Pb0.955La0.03(Zr0.42Sn0.40Ti0.18)O3 ceramics near its phase transition

Phase transition and pyroelectric behaviors of Pb0.955La0.03(Zr0.42Sn0.40Ti0.18)O3 (PLZST) ceramics were investigated as functions of temperature and electric field. Pyroelectric coefficient about 160×10−8 C cm−2 K−1 is detected at the electric-field-induce ferroelectric (FEIN) to antiferroelectric phase transition for the poled samples. Reversible pyroelectric response with a pyroelectric coefficient maximum about 50×10−8 C cm−2 K−1 is obtained when a dc bias is applied on the depoled sample simultaneously.

Enhanced polarization switching and energy storage properties of Pb0.97La0.02(Zr0.95Ti0.05)O3 antiferroelectric thin films with LaNiO3 oxide top electrodes

Polarization switching and energy storage properties of highly (100) oriented antiferroelectric (AFE) (Pb,La)(Zr,Ti)O3 thin films (≤250 nm) deposited via a sol-gel process with both LaNiO3 and Pt top electrodes were investigated. By using LaNiO3 top electrodes, the energy density as well as energy efficiency can be enhanced by 4.6 J/cm3 and 11%, respectively. Furthermore, the films with LaNiO3 top electrodes are more capable of providing high energy density over a wide temperature regime above room temperature compared to Pt. This work clearly highlights that oxide top electrodes can greatly improve the energy storage performance of antiferroelectric thin film capacitors.

Microwave properties of epitaxial (111)-oriented Ba0.6Sr0.4TiO3 thin films on Al2O3(0001) up to 40 GHz

Perovskite Ba0.6Sr0.4TiO3 (BST) thin films have been grown on Al2O3(0001) substrates without/with inserting an ultrathin TiOx seeding layer by rf magnetron sputtering. X-ray diffraction and pole figure studies reveal that the film with the TiOx layer (12-A-thick) is highly oriented along the (111) direction and exhibits a good in-plane relationship of BST(111)∥Al2O3(0001). The high frequency dielectric measurements demonstrate that the complex permittivity (e=e′−je″) is well described by a Curie–von Scheidler dispersion with an exponent of 0.40. The resulting epitaxial BST films show high permittivity (∼428) and tunability (∼41%, at 300 kV/cm and 40 GHz) and their microwave properties (1–40 GHz) potentially could be made suitable for tunable devices.

Mechanical and electrical properties of small amount of oxides reinforced PZT ceramics

Abstract Piezoelectric PZT ceramics with small amount (0.1–1.0 wt.%) of oxides (Y 2 O 3 , MoO 3 , WO 3 ) were prepared by conventional sintering method. Small amount of second phase doped PZT ceramic with high fracture strength showed suitable piezoelectric properties for high power and high reliable actuator applications. Especially, the fracture strength of PZT/0.1 wt.% Y 2 O 3 composite was 1.5 times higher than that of monolithic PZT and the piezoelectric properties were also increased. When the second phase addition was up to 1.0 wt.%, the electrical properties were deteriorated due to the refinement of the microstructure of PZT ceramics.