ZrO2 and TiO2 modified lead-free (K0.5Na0.5)NbO3 (KNN) piezoelectric ceramics are prepared by a conventional solid-state reaction. The effect of acceptor doping on structural and functional ...properties is investigated. A decrease in the Curie temperature and an increase in the dielectric constant values are observed when doping. More interestingly, an increase in the coercive field Ec and remanent polarization Pr is observed. The piezoelectric properties are greatly increased when doping with small concentrations dopants. ZrO2 doped ceramic exhibits good piezoelectric properties with piezoelectric coefficient d33=134pC/N and electromechanical coupling factor kp=35%. It is verified that nonlinearity is significantly reduced. Thus, the creation of complex defects capable of pinning the domain wall motion is enhanced with doping, probably due to the formation of oxygen vacancies. These results strongly suggest that compositional engineering using low concentrations of acceptor doping is a good means of improving the functional properties of KNN lead-free piezoceramic system.
A-site deficient rare-earth doped barium zirconate titanate (BZT) ceramics (Ba1-yLn2y/3)Zr0.09Ti0.91O3 (Ln = La, Pr, Nd, Gd) were obtained by a modified solid-state reaction. Perovskite-like ...single-phase compounds were confirmed from XRD data. Morphological analysis of the sintered samples showed that the addition of rare-earth ions inhibited grain growth and changed the grain morphology. The effect of rare-earth additions to BZT on the phase transition and dielectric properties was analysed. A dramatic fall in the transition temperature occurred when BZT was doped with rare-earths. The diffusivity of the phase transition increased and relaxor-type behaviour was induced due to both increased lanthanide content and the increased ionic radius of the dopant. High values of dielectric tunability were obtained for lanthanum-doped BZT. A direct relationship between transition temperature and tunability is discussed. Low permittivity and highly tunable materials were obtained by the substitution of rare-earths into BZT ceramics.
Dense lead-free (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3 piezoelectric ceramics are prepared by the conventional mixed oxide method. The effect of different sintering conditions (synthetic air, O2 ...and Ar) on some structural, dielectric and piezoelectric properties is studied. A long sintering time (16h) promotes the formation of a secondary phase, which is assigned to K3LiNb6O17, tetragonal tungsten-bronze. High values of longitudinal piezoelectric constant are obtained when ceramics are sintered under Ar or O2 for low dwell time (2h). However, the nonlinear response turns out to be significantly dependent on the sintering atmosphere. Results are discussed taking into account the formation of complex defects capable of pinning domain wall when oxygen vacancies are created by sintering. Thus, sintering in an inert atmosphere appears to be a good way of reducing nonlinear response in KNN-based piezoceramics.
Detailed analyses of WMAP and Planck data can have significant implications for noncyclic pre-Big Bang approaches incorporating a new fundamental scale beyond the Planck scale and, potentially, new ...ultimate constituents of matter with unconventional basic properties as compared to standard particles. Cosmic-ray experiments at the highest energies can also yield relevant information. Hopefully, future studies will be able to deal with alternatives: i) to standard physics for the structure of the physical vacuum, the nature of space-time, the validity of quantum field theory and conventional symmetries, the interpretation of string-like theories...; ii) to standard cosmology concerning the origin and evolution of our Universe, unconventional solutions to the cosmological constant problem, the validity of inflationary scenarios, the need for dark matter and dark energy... Lorentz-like symmetries for the properties of matter can then be naturally stable space-time configurations resulting from more general primordial scenarios that incorporate physics beyond the Planck scale and describe the formation and evolution of the physical vacuum. A possible answer to the question of the origin of half-integer spins can be provided by a primordial spinorial space-time with two complex coordinates instead of the conventional four real ones, leading to a really new cosmology. We discuss basic questions and phenomenological topics concerning noncyclic pre-Big Bang cosmologies and potentially related physics.
Mn2+-doped (K,Na,Li)(Nb,Ta,Sb)O3 lead-free piezoelectric ceramics have been prepared by a conventional sintering technique. The effects of Mn2+ doping on the phase structure, microstructure and ...ferro-piezoelectric properties of the ceramics have been evaluated. MnO doping modifies the (K,Na,Li)(Nb,Ta,Sb)O3 structure, giving rise to the appearance of a TTB-like secondary phase and to changes on the orthorhombic to tetragonal phase transition temperature. The modification of this temperature induces a reduction of the piezoelectric constants, which is accompanied by an increase on the mechanical quality factor. Mn2+ ions incorporate into the perovskite structure in different off ways depending on their concentration.
With the present understanding of data, the observed flux suppression for ultra-high energy cosmic rays (UHECR) at energies above 4.10sup 19 eV can be a signature of the Greisen-Zatsepin-Kuzmin (GZK) ...cutoff or be related to a similar mechanism. But it may also correspond, for instance, to the maximum energies available at the relevant sources. In both cases, violations of special relativity modifying cosmic-ray propagation or acceleration at very high energy can potentially play a role. Other violations of fundamental principles of standard particle physics can also be relevant at these energies. In particular, UHECR data would in principle allow to set bounds on Lorentz symmetry violation (LSV) in patterns incorporating a privileged local reference frame (the "vacuum rest frame", VRF). We present an updated discussion of the topics, including experimental prospects, new potentialities for high-energy cosmic ray phenomenology and the possible link with unconventional pre-Big Bang scenarios, superbradyon patterns... The subject of a possible superluminal propagation of neutrinos at accelerator energies is also dealt with.
Lanthanum lithium titanate thin films were grown by Pulsed Laser Deposition. La
0.57Li
0.29TiO
3 dense films with smooth surfaces were obtained after optimization of the growth parameters. Such films ...deposited at 700 °C under 15 Pa are nano-crystalline with domains corresponding to the cubic and tetragonal modifications of this phase. In relation to the measured conductivities/activation energy and to previous works, we clearly underlined that the films of practical interest, prepared at relatively low temperature, are predominantly formed from the tetragonal ordered phase.
Heterovalent B-site MgO substitution in the Nd2Zr2O7-system (Nd2Zr2−xMgxO7−x) has been explored. The pyrochlores were synthesized by a polymeric sol-gel method and characterized by X-ray diffraction ...(XRD), Raman spectroscopy and Scanning Electron Microscopy to determine structure, phase composition and microstructure. Impedance Spectroscopy (IS) was employed to study the electrical behavior of the ceramics over the ranges 200–800 °C and under pure N2 and O2. The XRD showed that the solid solution limit was x > 0.02 and all the materials show a cubic Fd3̅m structure. The Raman results confirm the structural disorder created by the introduction of Mg2+ and the subsequent generation of oxygen vacancies. The IS data shows a dramatical increase of the oxide-ion conductivity when doping and that the conductivity depends strongly on the atmosphere, leading to p-type semiconductivity under pure O2 atmosphere. The present study highlights the use of heterovalent dopants to drastically increase the oxide-ion conductivity of pyrochlore-like materials.
Rare-earth (
RE) doped Ba(Zr,Ti)O
3 (BZT) thin films were prepared by rf-magnetron sputtering from a Ba
0.90
Ln
0.067Zr
0.09Ti
0.91O
3 (
Ln=La, Nd) target. The films were deposited at a substrate ...temperature of 600
°C in a high oxygen pressure atmosphere. X-ray diffraction (XRD) patterns of
RE-BZT films revealed a 〈001〉 epitaxial crystal growth on Nb-doped SrTiO
3, 〈001〉 and 〈011〉 growth on single-crystal Si, and a 〈111〉-preferred orientation on Pt-coated Si substrates. Scanning electron microscopy (SEM) showed uniform growth of the films deposited, along with the presence of crystals of about half-micron size on the film's surface. Transmission electron microscopy (TEM) evidenced high crystalline films with thicknesses of about 100
nm for 30
min of sputtering. Electron-probe microanalysis (EPMA) corroborated the growth rate (3.0–3.5
nm/min) of films deposited on Pt-coated Si substrates. X-ray photoelectron spectroscopy (XPS), in depth profile mode, showed variations in photoelectron Ti 2
p doublet positions at lower energies with spin-orbital distances characteristic of BaTiO
3-based compounds. The XPS analysis revealed that lanthanide ions positioned onto the
A-site of the BZT-perovskite structure increasing the MO
6-octahedra distortion (
M=Ti, Zr) and, thereby, modifying the Ti–O binding length. Polarization-electric field hysteresis loops on Ag/
RE-doped BZT/Pt capacitor showed good ferroelectric behavior and higher remanent polarization values than corresponding non-doped system.
XPS narrow-scan spectra of Ti 2
p doublets of the Nd-doped BZT films deposited on Pt-coated Si substrate.
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