Electromechanical strain and bipolar fatigue in Bi(Mg1/2Ti1/2)O3-(Bi1/2K1/2)TiO3-(Bi1/2Na1/2)TiO3 ceramics

Lead-free ceramics of composition Bi(Mg₁/₂Ti₁/₂)O₃-(Bi₁/₂K₁/₂)TiO₃-(Bi₁/₂Na₁/₂)TiO₃ were prepared using solid state synthesis techniques. The dielectric spectra showed a Tmax of more than 320 °C for all compositions, and the transitions became increasingly diffuse as the Bi(Mg₁/₂Ti₁/₂)O₃ content increased. A lower temperature transition, indicating a transformation from an ergodic to a non-ergodic relaxor state, was also seen for all compositions, and this transition temperature decreased as the mole fraction of Bi(Mg₁/₂Ti₁/₂)O₃ increased. The composition with 1% Bi(Mg₁/₂Ti₁/₂)O₃ showed characteristic ferroelectric-like polarization and strain hysteresis. However, compositions with increased Bi(Mg₁/₂Ti₁/₂)O₃ content became increasingly ergodic at room temperature with pinched polarization loops and no negative strain. Among these compositions, the magnitude of d₃₃* increased with Bi(Mg₁/₂Ti₁/₂)O₃ content, and the composition with 10% Bi(Mg₁/₂Ti₁/₂)O₃ exhibited a d₃₃* of 422 pm/V. Fatigue measurements were conducted on all compositions and while the 1% Bi(Mg₁/₂Ti₁/₂)O₃ composition exhibited a measurable, but small loss in maximum strain after a million cycles; all the other compositions from 2.5% to 10% Bi(Mg₁/₂Ti₁/₂)O₃ were essentially fatigue-free. Lastly, optical and alternating current impedance measurements were employed to identify intrinsic conduction as the dominant conduction mechanism. These compositions were also highly insulating with high resistivities (~10⁷ Ω-cm) at high temperatures (440 °C)

Effects of NiO nanoparticles on the magnetic properties and diffuse phase transition of BZT/NiO composites

A new composite system, Ba(Zr0.07Ti0.93)O3 (BZT93) ceramic/NiO nanoparticles, was fabricated to investigate the effect of NiO nanoparticles on the properties of these composites. M-H hysteresis loops showed an improvement in the magnetic behavior for higher NiO content samples plus modified ferroelectric properties. However, the 1 vol.% samples showed the optimum ferroelectric and ferromagnetic properties. Examination of the dielectric spectra showed that the NiO additive promoted a diffuse phase transition, and the two phase transition temperatures, as observed for BZT93, merged into a single phase transition temperature for the composite samples

Bipolar piezoelectric fatigue of Bi(Zn0.5Ti0.5)O3-(Bi0.5K0.5)TiO3-(Bi0.5Na0.5)TiO3 Pb-free ceramics

The piezoelectric fatigue behavior of Pb-free ceramics based on solid solutions of Bi(Zn₀.₅Ti₀.₅)O₃-(Bi₀.5K₀.₅)TiO₃-(Bi₀.₅Na₀.₅)TiO₃ was characterized at 50 kV/cm after 10⁶ bipolar cycles. Ferroelectric compositions containing 2.5% Bi(Zn₀.₅Ti₀.₅)O₃ exhibited only minor losses in maximum strain (~10%). In compositions with 5% Bi(Zn₀.₅Ti₀.₅)O₃ that exhibit large electric field-induced strains, the electromechanical strain actually increased 4%, exhibiting essentially fatigue free behavior. This finding demonstrates that these materials have excellent potential for demanding high cycle applications such as microelectromechanical systems actuators. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4738770]KEYWORDS: Melville, NY 11747-4501 USA, Zirconate titanate ceramics, 2 Huntington quadrangle, Ste 1 N 0 1, Circulation & fulfillment di

Phase transitions and ferroelectric properties in BiScO3-Bi(Zn1/2Ti1/2)O3-BaTiO3 solid solutions

Ceramics solid solutions within the ternary perovskite system Bi(Zn1/2Ti1/2)O3-BiScO3-BaTiO3 were synthesized via solid-state processing techniques. The crystal structure of sintered ceramics was analyzed by x-ray diffraction. A stable perovskite phase was obtained for all compositions with a BaTiO3 content greater than 50 mol %. Furthermore, a change in symmetry from pseudocubic to tetragonal was observed as the mole fraction of BaTiO3 increased. Dielectric measurements show a dielectric anomaly associated with a phase transformation over the temperature range of 30 °C–210 °C for all compositions. Examination of the polarization hysteresis behavior revealed weakly nonlinear hysteresis loops. With these data, ferroelectric phase diagrams were derived showing the transition between the pseudocubic relaxor behavior to the tetragonal normal ferroelectric behavior. This transition was also correlated with changes in the diffuseness parameter

Role of point defects in bipolar fatigue behavior of Bi(Mg[subscript 1/2]Ti[subscript 1/2])O₃ modified (Bi[subscript 1/2]K[subscript 1/2])TiO₃-(Bi[subscript 1/2]Na[subscript 1/2])TiO₃ relaxor ceramics

Lead-free Bi(Mg₁/₂Ti₁/₂)O₃-(Bi₁/₂K₁/₂)TiO₃-(Bi₁/₂Na₁/₂)TiO₃ (BMT-BKT-BNT) ceramics have been shown to exhibit large electromechanical strains under high electric fields along with negligible fatigue under strong electric fields. To investigate the role of point defects on the fatigue characteristics, the composition 5BMT-40BKT-55BNT was doped to incorporate acceptor and donor defects on the A and B sites by adjusting the Bi/Na and Ti/Mg stoichiometries. All samples had pseudo-cubic symmetries based on x-ray diffraction, typical of relaxors. Dielectric measurements showed that the high and low temperature phase transitions were largely unaffected by doping. Acceptor doping resulted in the observation of a typical ferroelectric-like polarization with a remnant polarization and strain hysteresis loops with significant negative strain. Donor-doped compositions exhibited characteristics that were indicative of an ergodic relaxor phase. Fatigue measurements were carried out on all of the compositions. While the A-site acceptor-doped composition showed a small degradation in maximum strain after 10⁶ cycles, the other compositions were essentially fatigue free. Impedance measurements were used to identify the important conduction mechanisms in these compositions. As expected, the presence of defects did not strongly influence the fatigue behavior in donor-doped compositions owing to the nature of their reversible field-induced phase transformation. Even for the acceptor-doped compositions, which had stable domains in the absence of an electric field at room temperature, there was negligible degradation in the maximum strain due to fatigue. This suggests that either the defects introduced through stoichiometric variations do not play a prominent role in fatigue in these systems or it is compensated by factors like decrease in coercive field, an increase in ergodicity, symmetry change, or other factors.This is the publisher’s final pdf

Effects of ZrO₂ additions on the dielectric properties of CaCu₃Ti₄O₁₂

The dielectric spectra of CaCu₃Ti₄O₁₂ is characterized by a large permittivity (εᵣ>10 000) with only a weak dependence on temperature over the temperature range 200–400 K. In this work, doping with 0.1–1.0 wt % ZrO₂ has been shown to dramatically reduce the dielectric loss. At 0.5 wt % ZrO₂, tan δ remains below 0.05 over the frequency range 50 Hz–30 kHz and is just 0.065 at 100 kHz. While there is some diminution of the permittivity (εᵣ≈5000 at 10 kHz) Zr-doped ceramics, exhibited very little bias dependence (∆C/C₀<1.0% up to 40 V). In summary, results suggest that ZrO₂ doping is an effective method for maintaining a high permittivity and low loss over a broad range in temperature, bias, and frequency.Keywords: zirconium compounds, copper compounds, doping, dielectric losses, dielectric materials, calcium compounds, permittivit

Electromechanical strain in Bi(Zn1/2Ti1/2)O3–(Bi1/2Na1/2)TiO3–(Bi1/2K1/2)TiO3 solid solutions

Solid solutions ceramics of the Bi(Zn0.5Ti0.5)O-3-(Bi0.5K0.5)TiO3-(Bi0.5Na0.5)TiO3 ternary system for <20 mol. % BZT were created and confirmed to be single phase using x-ray diffraction. The dielectric dispersion showed decreasing T-max of the dielectric spectrum with a broadening of the transition with increasing BZT content. At 2.5BZT-40BKT-57.5BNT, a secondary transition commonly observed for morphotropic phase boundary (MPB) BNT-BKT was observed. The ferroelectric behavior of the system was characterized by a transition where the polarization hysteresis showed a severe pinching effect on remanent polarization (20.8 mu C/cm(2) at 2.5% BZT) as BZT contents was increased (P-r = 2.3 mu C/cm(2) at 20% BZT). Similarly, as the temperature increased to 175 degrees C, the remanent polarization of the 2.5% BZT composition significantly reduced to 2.1 mu C/cm(2). The onset of this transition corresponds to the lower temperature frequency dispersion observed in the dielectric spectrum. The strain hysteresis experienced analogous transition to the polarization, with a change in shape from typical ferroelectric butterfly to a complete loss of negative strain as BZT concentration increased. Maximum strain values of 0.33% were observed at 5-40-55 accompanied by a large d(33)* = 547 pm/V. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4714346]This is the publisher’s final pdf. The published article is copyrighted by American Institute of Physics and can be found at: http://jap.aip.org/.Keywords: Temperature, Perovskite, Free piezoelectric ceramics, Lead free ceramics, Morphotropic phase boundaryKeywords: Temperature, Perovskite, Free piezoelectric ceramics, Lead free ceramics, Morphotropic phase boundar

Effects of NiO nanoparticles on the magnetic properties and diffuse phase transition of BZT/NiO composites

A new composite system, Ba(Zr[subscript 0.07]Ti[subscript 0.93])O₃ (BZT93) ceramic/NiO nanoparticles, was fabricated to investigate the effect of NiO nanoparticles on the properties of these composites. M-H hysteresis loops showed an improvement in the magnetic behavior for higher NiO content samples plus modified ferroelectric properties. However, the 1 vol. % samples showed the optimum ferroelectric and ferromagnetic properties. Examination of the dielectric spectra showed that the NiO additive promoted a diffuse phase transition, and the two phase transition temperatures, as observed for BZT93, merged into a single phase transition temperature for the composite samples.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Springer. The published article can be found at: http://www.nanoscalereslett.com/.Keywords: microstructure, ceramics, composites, electrical properties, magnetic propertie

The KELT Follow-Up Network And Transit False-Positive Catalog: Pre-Vetted False Positives For TESS

The Kilodegree Extremely Little Telescope (KELT) project has been conducting a photometric survey of transiting planets orbiting bright stars for over 10 years. The KELT images have a pixel scale of ~23\u27\u27 pixel⁻¹—very similar to that of NASA\u27s Transiting Exoplanet Survey Satellite (TESS)—as well as a large point-spread function, and the KELT reduction pipeline uses a weighted photometric aperture with radius 3\u27. At this angular scale, multiple stars are typically blended in the photometric apertures. In order to identify false positives and confirm transiting exoplanets, we have assembled a follow-up network (KELT-FUN) to conduct imaging with spatial resolution, cadence, and photometric precision higher than the KELT telescopes, as well as spectroscopic observations of the candidate host stars. The KELT-FUN team has followed-up over 1600 planet candidates since 2011, resulting in more than 20 planet discoveries. Excluding ~450 false alarms of non-astrophysical origin (i.e., instrumental noise or systematics), we present an all-sky catalog of the 1128 bright stars (6 \u3c V \u3c 13) that show transit-like features in the KELT light curves, but which were subsequently determined to be astrophysical false positives (FPs) after photometric and/or spectroscopic follow-up observations. The KELT-FUN team continues to pursue KELT and other planet candidates and will eventually follow up certain classes of TESS candidates. The KELT FP catalog will help minimize the duplication of follow-up observations by current and future transit surveys such as TESS

Improving Participation of Engineering Students Studying Abroad: An International Dual Degree Program in Materials Science and Mechanical Engineering

Without AbstractThis is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Springer and can be found at: http://link.springer.com/journal/11837