J. G. Zhu

Enhanced dielectric and ferroelectric properties of Pb(Zr0.8Ti0.2)O3∕Pb(Zr0.2Ti0.8)O3 multilayered thin films prepared by rf magnetron sputtering

The Pb(Zr1−xTix)O3 multilayered films consisting of Pb(Zr0.8Ti0.2)O3 and Pb(Zr0.2Ti0.8)O3 layers were deposited on LaNiO3(110)∕Pt∕Ti∕SiO2∕Si substrates by rf magnetron sputtering. All films comprise five periodicities, the layer thicknesses of rhombohedral (dR) and tetragonal (dT) phases in one periodicity are varied. The LaNiO3 buffer layer leads to the (101)∕(110) orientation of the films. The electrical properties of the films were investigated as a function of dR∕dT. The films with dR∕dT=1:2 possess enhanced dielectric and ferroelectric properties. The mechanism of the enhanced electrical properties was discussed, and it was found that the strain is also an important factor to affect electrical properties.

Microstructure, dielectric, and piezoelectric properties of (Li, Ag, Ta) modified (K0.50Na0.50)NbO3 lead-free ceramics with high Curie temperature

(1−x)[(K0.4725Na0.4725Li0.055)NbO3]−xAgTaO3[(1−x)KNNL−xAT] lead-free ceramics have been prepared by the conventional mixed oxide method. Effect of the AgTaO3 (AT) content on the microstructure and electrical properties of (1−x)KNNL−xAT ceramics were systematically investigated. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal phases was identified in the composition range of 0.015<x<0.025. The materials near the MPB exhibit a strong compositional dependence and enhanced electrical properties along with high Curie temperature. It is found that the samples with 2 mol % AT exhibit relatively good electrical properties along with high Curie temperature: the piezoelectric constant d33 and Curie temperature TC reach 237 pC/N and 470 °C, respectively; the electromechanical coupling coefficient of the planar mode kp reaches 39%; and the remnant polarization (Pr) is 29.4 μC∕cm2 with a coercive field (Ec) of 13.6 kV/cm. These results show that (1−x)KNNL−xAT is a promising candidate material f...

Preparation and Characterization of (1 — x) Pb(Mg1/3Nb2/3) O3 — x PbTiO3 Electrocaloric Ceramics

Lead magnesium niobate Pb(Mg1/3Nb2/3)O3 — lead titanate PbTiO3 [abbr. as (1 — x) PMN — x PT] ferroelectric ceramics with different excesses of MgO and PbO were systematically studied under different processing conditions for ferroelectric refrigeration application. It was found that the excess amount of MgO and PbO, and the sintering temperature have great effect on the crystallographic properties of the ceramics. In our experiments, (1 — x) PMN —x PT (x = 0.08, x = 0.10, and x = 0.25 respectively) with the excesses of 2 mol% MgO and 2 mol% PbO ceramics sintered at 1250 °C/1 hour possess the desired perovskite structures and large electrocaloric temperature change (ΔT = 1 K and more) in the vicinity of room temperature under a dc electric field of 1.5 kV/mm. It is expected that (1 — x) PMN — x PT electrocaloric ceramics could be applied for cascade refrigeration near room temperature.

The orientation of (Pb,La)TiO3 thin films grown on different substrates by multi-ion-beam reactive cosputtering technique

Highly oriented or epitaxial (Pb,La)TiO3 thin films have been grown on substrates of amorphous optical glasses and single crystal silicon (111), sapphire (0001) and (1102) wafers by a multi-ion-beam reactive cosputtering (MIBRECS) technique. The deposition conditions, such as incident Pb/Ti ratio, will greatly affect the orientation of PLT thin films. It was found that in addition to other advantages, highly oriented thin films can easily be grown by using this technique. MIBRECS may also be a promising technique for investigating the growth mechanisms of multi-component oxide thin films deposited by ion beam sputtering.

Thermally driven grain boundary migration and melting in Cu

With molecular dynamics simulations, we systematically investigate melting of a set of Σ3〈110〉70.53° tilt grain boundaries (GB) in Cu bicrystals, including coherent twin boundaries (CTBs), 12 asymmetric tilt grain boundaries (ATGBs), and symmetric incoherent twin boundaries (SITBs), in the order of increasing length weight of SITB or GB energy. ATGBs decompose into CTBs and SITBs, which migrate and coalesce as a result of internal stress relaxation. GBs can be superheated or premelted, and GB melting temperature decreases exponentially with increasing SITB weight, owing to the systematics in GB microstructure. GB melting nucleates at disordered CTB-SITB junctions, and grows along SITBs and then into grain interiors, with the solid-liquid interfaces preferentially aligned with {111}.

Study of (Bi4−xLa x ) Ti3O12 Powders and Ceramics Prepared by Sol-Gel Method

La-modified (Bi4−xLax)Ti3O12 (abbreviated as BLT) powders were prepared by sol-gel processing methods. The powders were characterized by differential thermal analysis (DTA) and laser-diffraction particle-size analysis. The (Bi4−xLax)Ti3O12 ceramics were prepared from the powders and characterized by X-ray diffraction (XRD). The results indicate that the sol-gel method can be used to prepare nanometer powder for the new types of BLT ferroelectric ceramics. The solid reaction of BLT powders occurs at 730°C approximately resulting in the growth of BLT grain. The average grain size may be varied in the range 60–500 nm, depending on the calcination temperature of the powders. The (Bi4−xLax)Ti3O12 ceramics prepared from the powders were polycrystalline materials with completely monoclinic (Bi4−xLax)Ti3O12 phase.

Ferroelectric integrated thin films

Abstract In recent years, great effort has been paid to “Integrated Ferroelectrics”, i.e. the integration of ferroelectric thin films with Si or GaAs chips for developing new devices or systems. Another interesting and potential important area for the investigation of ferroelectric thin films may be the integration of ferroelectric thin films with related functional films, such as piezoelectric and nonlinear optic thin films, for developing multifunctional devices or smart film devices by using the nonlinear or cross-coupling effects based on the interaction of elastic, thermal, electric, magnetic and optical fields in ferroelectric thin films. In this paper, we present some fundamental aspects of ferroelectric integrated thin films from both phenomenological and fabrication points of view, and give some examples of potential devices which can be made from ferroelectric integrated thin films.

High permittivity Bi24Fe2O39 thin films prepared by a low temperature process

High permittivity Bi24Fe2O39 (BFO) thin films have been deposited on platinized silicon substrates by a low temperature process combining rf magnetron sputtering at room temperature and postdeposition annealing at 450 °C. A nearly pure tetragonal crystal structure with highly (201)-preferred orientation, determined by x-ray diffraction, was formed in the BFO thin film. The BFO film not only exhibits high dielectric permittivity (er=113) and relatively low loss tangent (tan δ=0.012), but also shows a fairly small quadratic voltage coefficient of capacitance (α∼800 ppm/V2) and a small temperature coefficient of capacitance (αT∼790 ppm/°C). Moreover, the leakage current density, obeying the Fowler–Nordheim tunneling mechanism, remains at a reasonably low level with the increase in applied electric field (J∼10−6–10−4 A/cm2 under E=400 kV/cm). These attractive dielectric and electrical properties make the low temperature processed Bi24Fe2O39 thin film a promising candidate for high-k dielectric applications in...

Temperature stability of lead-free piezoelectric ceramics of perovskite Bi 0.5 Na 0.5 TiO 3 and K 0.5 Na 0.5 NbO 3 families

From the viewpoint of application, the temperature stability of the electrical properties of the lead-free piezoelectric ceramics is very important. Therefore, it is important to study the temperature stability of the electrical properties of perovskite Bi<inf>0.5</inf>Na{0.5}TiO<inf>3</inf> (BNT)- and K<inf>0.5</inf>Na<inf>0.5</inf>NbO<inf>3</inf> (KNN)-based (Bi<inf>0.47</inf>Na<inf>0.47</inf>)Ba<inf>0.06</inf>TiO<inf>3</inf> (BNBT6) and (K<inf>0.49</inf>Na<inf>0.49</inf>)Li<inf>0.02</inf>Nb<inf>0.95</inf>Sb<inf>0.05</inf>O<inf>3</inf> (KNLNS2-5) were selected, and the temperature stability of the dielectric, piezoelectric, and ferroelectric properties of the two kinds of ceramics were compared from the point of view of the application of the ceramics. It was found that the piezoelectric properties of KNLNS2-5 ceramics are much more stable in the orthorhombic phase than in the tetragonal phase. This is an important clue to obtain excellent piezoelectric properties along with good temperature stability for KNN-based ceramics.

Deposition process effect on crystalline structure of (Pb, La) TiO3 thin films by multi – ion – beam reactive cosputtering technique

Abstract Multi—ion—beam reactive cosputtering (MIBRECS) technique is a promising technique for preparing multi—component oxide thin films. However, the deposition processes are critically important for preparing thin films with prospected stoichiometry and good quality. In this paper, the effect of deposition processes, such as substrate temperature, ion beam energy and current, and the postdeposition annealing conditions on the composition and crystalline structure of (Pb, La) TiO3 ferroelectric thin films prepared by MIBRECS technique are reported.