Improved Fluorescence from Tm-Ho- and Tm-Ho-Eu-Codoped Transparent PbF2 Glass-Ceramics for S+-Band Amplifiers

Tm³⁺-Ho³⁺- and Tm³⁺-Ho³⁺-Eu³⁺-ion-codoped oxyfluoride transparent glass-ceramics containing PbF₂ nanocrystals were prepared, and the near-infrared fluorescence properties of the Tm³⁺ ions were investigated for their potential use as a 1.4 μm amplifier. For all samples, the lifetime of the Tm³⁺:³ H ₄ level increased with heat treatment because of the decrease of the phonon energy as PbF₂ crystals were formed. Moreover, it was revealed that codoping with Ho³⁺ or Eu³⁺ was effective in suppressing the lifetime of the Tm³⁺:³ F ₄ level by energy transfer to the Ho³⁺:⁵ I ₇ or Eu³⁺:⁷ F ₆ level. For the codoped samples, the heat treatments decreased the Tm³⁺:³ F ₄ lifetime and increased the Tm³⁺:³ H ₄ lifetime. This was attributed to the concentration of rare-earth ions in the fluoride crystallites. These properties improved the population inversion of the 1.4 μm transition.     

Reversible luminescence modulation of Ho‐doped K0.5Na0.5NbO3 piezoelectrics with high luminescence contrast

A significant luminescence modulation behavior based on photochromic reactions was observed in Ho³⁺‐doped (Na_0.52K_0.48)_0.92Li_0.08NbO₃ ceramics, fabricated by the conventional solid‐state reaction method. Under visible light irradiation (407 nm) for 20 second, the samples changed pale gray from initial pale green, and returned to their original color by a thermal stimulus of 230°C for 10 minutes, showing typical photochromic phenomenon. Under 453 nm excitation, the samples exhibited strong green emission at 551 nm. Interestingly, their green emission intensity can be effectively tailored by controlling photochromic reaction processes (irradiation wavelength and time), and the luminescent modulation ratio (ΔR_t) reaches up to 77%. And, the ΔR_t value has no any obvious degradation after 10 cycles by alternating visible light irradiation and thermal stimulus, showing excellent reversibility. These results make it potential applications in many fields as a kind of multifunctional material.     

Thermal stability and electric‐field‐induced strain behaviors for PIN‐PSN‐PT piezoelectric ceramics

Pb (In_1/2Nb_1/2) O₃‐Pb (Sc_1/2Nb_1/2) O₃‐PbTiO₃ (PIN‐PSN‐PT) ternary ceramics with compositions near morphotropic phase boundary (MPB) were fabricated by solid‐state‐sintering process. Dielectric and piezoelectric properties of xPIN‐yPSN‐zPT (x = 0.19, 0.23 and z = 0.365, 0.385) ceramics were investigated as a function of temperature, showing high T_r‐t and T_c on the order of 160 ~ 200°C and 280 ~ 290°C, respectively. The xPIN‐yPSN‐0.365PT (x = 0.19 and 0.23) ceramics do not depolarize at the temperature up to 200°C, showing a better thermal stability when compared to the state‐of‐the‐art relaxor‐PbTiO₃ systems. A slight variation (<9%) of k_p, k_t, and k₃₃ was observed in the temperature range of 25°C‐160°C for xPIN‐yPSN‐0.385PT (x = 0.19 and 0.23) ceramics. Rayleigh analysis was employed to quantify the contribution of domain wall motion to piezoelectric response, where the domain wall contribution was found to increase with composition approaching MPB for PIN‐PSN‐PT system.     

Intrinsic Elastic, Dielectric, and Piezoelectric Losses in Lead Zirconate Titanate Ceramics Determined by an Immittance-Fitting Method

The material coefficients of "soft" and "hard" lead zirconate titanate (PZT) ceramics were determined as complex values by the nonlinear least-squares-fitting of immittance data measured for length-extensional bar resonators. The piezoelectric d -constant should be a complex value to obtain a best fitting between observed and calculated results. Because the elastic, dielectric, and piezoelectric losses determined in this process were not "intrinsic" losses, a calculation process to evaluate the "intrinsic" losses was proposed. It was confirmed that the intrinsic losses were smaller than the corresponding extrinsic losses. The intrinsic piezoelectric loss existed in both soft and hard PZTs; ∼50% of the loss of piezoelectric d -constant was derived from the elastic and dielectric losses. The most notable difference between the soft and hard PZTs was observed in their elastic losses.     

Composition-independent Curie point (Tc) in ferroelectric (1 − x)PbTiO3–xBi(Li1/2Nb1/2)O3 solid solution

A new ferroelectric solid solution (1 − x)PbTiO₃–xBi(Li_1/2Nb_1/2)O₃ has been explored to develop high-temperature piezoelectric material. An interesting observation has been found regarding its Curie point (T_C) and tetragonal lattice strain (c/a − 1). With increasing composition (x), the Curie point (T_C) decreases up to x = 0.10 and thereafter remains constant. In concurrence with the T_C, the tetragonal lattice strain (c/a − 1) follows a similar trend. Neutron powder diffraction analysis suggests this anomalous behavior is due to the robust off-centering characteristic of the Bi⁺³ ion 6S² lone pair effect at the A-site compared to ions at B-site.     

Strength Evaluation of Piezoelectric Ceramics under Transient Thermal Environments

The strength of piezoelectric ceramics is analyzed for a plate suddenly exposed to an environmental medium of different temperatures. The admissible temperature jump the material can sustain is studied using the stress- and fracture-toughness-based failure criteria. The critical parameters governing the level of the transient thermal stress in piezoelectric ceramics are identified. Solutions are obtained for the maximum thermal shock that the plate can sustain without failure, under the conditions that (i) maximum local tensile stress equals the tensile strength of the ceramic, and (ii) maximum stress intensity factor for representative pre-existing cracks equals the fracture toughness of the ceramic.     

Crystallization and Dielectric Properties of SrO–BaO–Nb2O5–SiO2 Tungsten-Bronze Glass-Ceramics

The crystallization and dielectric properties of SrO–BaO–Nb₂O₅–SiO₂ glass-ceramics have been investigated. Glass-ceramics that contain strontium barium niobate (SBN) as a primary crystalline phase, which has a tungsten bronze structure, are produced. The formation of crystalline secondary phases also has been studied. The SBN phase shows evidence of both surface nucleation and bulk nucleation, and the crystals have an average composition of Sr_0.47Ba_0.53Nb₂O₆. The dendritic morphology of the SBN crystals has been examined. The SBN content and composite dielectric constant each has been studied as a function of heating temperature/time. The highest SBN content and dielectric constant obtained in the present study are 42 vol% and 180, respectively. The dielectric constant of the glass-ceramics is determined primarily by the SBN content and the residual glass phase. The dielectric constant of the randomly oriented SBN crystal in the glass-ceramics is calculated, using dielectric mixture rules, to be ∼400.     

Domain-Switching Criteria for Ferroelectric Materials Subjected to Electrical and Mechanical Loads

In this paper, existing domain-switching criteria are briefly reviewed and the predictions based on these domain-switching criteria are compared with the available experimental data for 180° and 90° domain switchings in lead lanthanum zirconate titanate (PLZT) and lead zirconate titanate (PZT), respectively. It is found that the predictions do not match the experimental results. Motivated by this observation, a new domain-switching criterion in terms of internal-energy density is proposed for combined mechanical and electrical loads. Based on consideration of the atomic structure of ferroelectric materials, it is recognized that 180° and 90° domain switchings result from different mechanisms and, thus, require different critical internal-energy densities for switching. The new criterion is found to yield very good predictions for both 180° and 90° domain switchings.     

Thickness‐dependent domain wall reorientation in 70/30 lead magnesium niobate‐ lead titanate thin films

Continued reduction in length scales associated with many ferroelectric film‐based technologies is contingent on retaining the functional properties as the film thickness is reduced. Epitaxial and polycrystalline lead magnesium niobate‐lead titanate (70PMN‐30PT) thin films were studied over the thickness range of 100‐350 nm for the relative contributions to property thickness dependence from interfacial and grain‐boundary low permittivity layers. Epitaxial PMN‐PT films were grown on SrRuO₃/(001)SrTiO₃, while polycrystalline films with {001}‐Lotgering factors >0.96 were grown on Pt/TiO₂/SiO₂/Si substrates via chemical solution deposition. Both film types exhibited similar relative permittivities of ~300 at high fields at all measured thicknesses with highly crystalline electrode/dielectric interfaces. These results, with the DC‐biased and temperature‐dependent dielectric characterization, suggest irreversible domain wall mobility is the major contributor to the overall dielectric response and its thickness dependence. In epitaxial films, the irreversible Rayleigh coefficients reduced 85% upon decreasing thickness from 350 to 100 nm. The temperature at which a peak in the relative permittivity is observed was the only measured small signal quantity which was more thickness‐dependent in polycrystalline than epitaxial films. This is attributed to the relaxor nature present in the films, potentially stabilized by defect concentrations, and/or chemical inhomogeneity. Finally, the effective interfacial layers are found to contribute to the measured thickness dependence in the longitudinal piezoelectric coefficient.     

Tunable Microwave Properties of Barium Titanate-Based Ferroelectric Glass-Ceramics

BaTiO₃-based ferroelectric glass-ceramics with the composition 0.65(Ba_{1− X} Sr _X )TiO₃·0.27SiO₂·0.08Al₂O₃ ( X = 0.2–0.6) were fabricated, and their tunable dielectric properties were measured at microwave frequency. Major crystalline phases that precipitated during thermal treatment up to 1000°C were (Ba,Sr)TiO₃, Ba₂TiSi₂O₈, and BaAl₂Si₂O₈. The Curie temperatures of the heated bulk samples were successfully tuned near room temperature at the composition between X = 0.2 and 0.3. A thick-film sample with X = 0.3 showed 27% tunability at 5 GHz under 10 kV/cm bias voltage.     

Toughening of Glass by a Piezoelectric Secondary Phase

A toughening concept for glass, based on exploiting the ferroelastic effect of piezoelectric particles embedded in a glass matrix, is described. It is hypothesized that the domains within a piezoelectric phase will align themselves in the direction of the stress field around an advancing crack, thus absorbing energy and contributing to toughening. A powder technology route was optimized to fabricate lead-containing glass-matrix composites with up to 30 wt% of a lead zirconate titanate (PZT) particulate phase. An increase in fracture toughness of >50% was achieved via the addition of 30 wt% of PZT particles. Although other toughening mechanisms could be excluded in the present composites, the actual contribution of piezoelectric toughening remains under investigation.     

Mechanosynthesis and Thermal Stability of Piezoelectric Perovskite 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 Powders

The mechanosynthesis of piezoelectric perovskite 0.92Pb(Zn_1/3Nb_2/3)O₃–0.08PbTiO₃ (PZN–PT) by direct mechanochemical activation of the constituent oxides has been studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). This and the PbO flux method are the only two procedures that have succeeded in synthesizing this phase, which has recently been shown to present very high electromechanical response. The thermal stability of the single perovskite phase powders has been studied by differential thermal analysis/thermogravimetry and by high-temperature XRD as a function of mechanical activation time and pressure. The phase was found to transform into a pyrochlore type structure at temperatures above 400°C. The transformation presented a significant time dependence, and it was slowed down by increasing mechanical activation time and by the application of pressures by hot pressing. Sintering experiments were accomplished and 85% density, 77% perovskite-phase ceramics were obtained after heating at 1000°C for 1 h. Hot pressing at this temperature failed to increase the percentage of perovskite phase. Results are discussed, and procedures for obtaining dense single-phase PZN–PT-based ceramics with ultrahigh piezoelectricity are proposed.     

Fabrication of Piezoelectric Ceramic/Polymer Composite Transducers Using Fused Deposition of Ceramics

The fused deposition of ceramics (FDC) technique was used to fabricate piezoelectric ceramic skeletons for the development of piezoelectric composite transducers with 2–2 connectivity for medical imaging. The green parts were designed to have 30 vol% lead zirconate titanate ceramic (PZT-5H) in the final composites. Physical characterization of the sintered samples revealed that 96% of the theoretical density was achieved. Optical microscopy showed that defects due to the FDC mode of deposition, such as small roads and bubbles, were eliminated, because of improvements in powder processing. The electromechanical properties of the final composites were similar to the properties that were obtained for conventionally made composites. A matching layer and a backing layer, as well as wires and an inductor, were added to each FDC composite to fabricate a functional medical imaging transducer. The devices were tested in water using a steel target 3.5 cm thick. Echoes from the target could be detected with all the transducers that were fabricated using FDC. The sensitivities of the transducers were similar to that of a commercial transducer. However, the ringing was much longer than that for a commercial transducer, because the backing layer was not optimized in the transducers that were fabricated using FDC.     

Cement-Based 0-3 Piezoelectric Composites

To meet the requirements of development for smart or intelligent structures in civil engineering, new functional materials that have good compatibility with civil engineering structural materials are needed. In this study, for the first time in the field of piezoelectric materials, cement-based 0-3 piezoelectric (PZT) composites were fabricated by the normal mixing and spreading method. The new materials have very good compatibility with portland cement concrete. The cement-based 0-3 piezoelectric composites were shown to have a slightly higher piezoelectric factor and electromechanical coefficient than those of 0-3 PZT/polymer composites with a similar content of PZT particles; thus, they are adequate for sensor application. There is potential for the application of cement-based 0-3 PZT composites in civil engineering because of their better piezoelectric properties and good compatibility with portland cement concrete.     

Functional and structural effects of layer periodicity in chemical solution‐deposited Pb(Zr,Ti)O3 thin films

This work investigates the role of crystallization layers’ periodicity and thickness on functional response in chemical solution‐deposited lead zirconate titanate thin films, with periodic, alternating Zr and Ti gradients normal to the surface of the film. The films were processed with a range of layer periodicities and similar total film thickness, in order to relate the number of layers and compositional oscillations to structural and functional response changes. Trends of increased extrinsic contributions to the dielectric and ferroelectric responses are observed with increasing layer periodicity, but are counterpointed by simultaneous reduction in intrinsic contributions to the same. Transmission electron microscopy reveals in‐plane crystallographic discontinuity at individual crystallization interfaces. Samples with smaller periodicity, and thus thinner layers, potentially suffer from grain size refinement and subsequent reduction in domain size, thereby limiting extrinsic contributions to the response. The strong compositional oscillations in samples with larger periodicity result in deep fluctuations to the tetragonal side of the phase diagram, potentially reducing intrinsic contributions to the response. Conversely, piezoresponse force microscopy results suggest that large chemical oscillations in samples with larger periodicity also result in closer proximity to the morphotropic phase boundary, as evidenced by local acoustic softening at switching, signaling potential field‐induced phase transitions.