Structural,optical and dielectric studies of novel non-linear Bisglycine Lithium Nitrate piezoelectric single crystal

The novel non-linear semiorganic Bisglycine Lithium Nitrate (BGLiN) single crystals were grown by slow evaporation technique. The structural analysis revealed that it belongs to non-centrosymmetric orthorhombic structure. The presence of various functional groups in the grown crystal was confirmed by FTIR and Raman analysis. Surface morphology of the grown crystal was studied by scanning electron microscopy. The optical studies show that crystal has good transmittance (more than 80%) in the entire visible region and a wide band gap (5.17 eV). The optical constants such as extinction coefficient (K), the reflectance (R) and refractive index (n) as a function of photon energy were calculated from the optical measurements. With the help of these optical constants the electric susceptibility (χ_c) and both the real (ε_r) and imaginary (ε_i) parts of the dielectric constants were also calculated which are required to develop optoelectronic devices. In photoluminescence studies, a broad emission band centered at 404 nm was found in addition to a small band at 352 nm. A broad transition (from 29 to 33 °C) was observed with low dielectric constant value. A high piezoelectric charge coefficient (d₃₃) of 14 pC/N was measured at room temperature which implies its usefulness for various sensor applications. The second harmonic generation efficiency of crystal was found to be 1.5 times to that of KDP. From thermo gravimetric analysis and differential thermal analysis, thermal stability and melting point (246 °C) were investigated. The dielectric behavior, optical characterization, piezoelectric behavior and the non-linear optical properties of the Bisglycine Lithium Nitrate single crystals were reported for the first time which established the usefulness of these crystals for various piezo- and opto-electronics applications.     

Finite Element Analysis of Stress Field Concentration Near the Edge of an Electrode

We study stress fields near the edge of an electrode by finite element method. Von Mises Stress near an electrode edge is calculated. The effect of the curvature of the electrode is examined. Stress concentration is observed and a technique for its reduction is suggested.     

Boosting transduction coefficient in BaTiO3-Based piezoceramic through phase boundary engineering

Transduction coefficient (d₃₃×g₃₃) is the core parameter for evaluating piezoelectric energy harvesting materials. However, due to the thermodynamic constraints, the synergistic variation between piezoelectric charge constant (d₃₃) and dielectric constant (ε_r) indeed hinder the further increase of d₃₃×g₃₃. Herein, an enhanced d₃₃×g₃₃ of 13,000 × 10^?15 m²/N was achieved in 0.80BaTiO₃-0.10CaTiO₃-0.10BaZrO₃ (BC_0.1ZT) lead-free solid solution for the first time through a phase boundary engineering strategy. The high d₃₃×g₃₃ mainly stems from non-synergistic variation of dielectric and piezoelectric performance in the rhombohedral-orthorhombic (R-O) phase boundary, in which the low ε_r comes from the increased domain size and reduced domain wall density; while the high configurational sensitivity of the unique domains to external electric field contributed to the high d₃₃. Our findings provide an alternative approach for enhanced energy harvesting performance by tracing the strategy of designing phase boundary to decouple d₃₃ and ε_r.     

Crystal structure and piezoelectric characteristics of various phases near the triple-point composition in PZ-PT-PNN system

Crystal structures and piezoelectric properties of PbZrO₃-PbTiO₃-Pb(Ni_1/3Nb_2/3)O₃ ceramics near the triple point composition, particularly characteristics of the pseudocubic phase, were investigated. The pseudocubic phase, which formed near the triple point composition, disappeared with increase in the PbZrO₃ content. The pseudocubic phase had the Pm3m cubic structure. The tetragonal-pseudocubic morphotropic phase boundary (MPB) structure was developed during the tetragonal-to-cubic phase transformation. However, the rhombohedral phase directly transformed to the cubic phase because the structure of pseudocubic phase was similar to the rhombohedral structure. The specimens with pseudocubic phase and the specimens near pseudocubic phase exhibited nano-sized domains and small coercive electric fields, revealing their low domain wall energies. These specimens exhibited second-order ferroelectric-to-paraelectric phase transition and low Curie temperatures, confirming their low domain wall energies. The enhanced dielectric and piezoelectric properties of these specimens could be attributed to their low domain wall energies.     

Microstructure and electrical performance of Sm2O3-doped BCTSG lead-free ceramics

This work aims to upgrade the comprehensive electrical properties of BaTiO₃-based ceramics (1-x)[(Ba_0.94Ca_0.06)(Ti_0.92Sn_0.08)]-xSm₂O₃-0.06 mol% GeO₂ [abbreviated as (1-x)BCTS-xSm-0.06G]. First, piezoceramics were synthesized via a conventional solid-state method. Next, the phase structures, surface topographies, ferroelectric domains were evaluated using XRD, XRD Rietveld refinements, SEM, OP-PFM, TEM. The results demonstrate that all the ceramics possess an orthorhombic-tetragonal (O-T) phase when at room temperature. Significantly, optimized piezoelectricity is gained at x = 0.03 mol% (piezoelectric constant of d₃₃ = 630 ± 20 pC/N and planar electromechanical coupling factor of k_p = 61%). The ferroelectric domains of ceramics were examined using OP-PFM and TEM, which ulteriorly indicate that the favorable piezoelectricity is attributed to the coexistence of the O-T phase boundary and the subdued energy density of the domain wall. Furthermore, all the ceramics are confirmed to be relaxor ferroelectrics, with the relaxor degree increasing with the increasing content of Sm₂O₃.     

Enhanced dielectric and piezoelectric response in PZT superlattice-like films by leveraging spontaneous Zr/Ti gradient formation

Spontaneous Zr/Ti gradient formation during crystallization in sol-gel-processed Pb(Zr_xTi_1−x)O₃ films is used to prepare superlattice-like (SL), highly (1 0 0)-oriented thin films on Pt/Ti/SiO₂/Si substrates. SLs with stacking periodicity ranging from 13 up to 60 nm are synthesized with compositional gradient normal to the film surface and composition centered at x ≈ 0.53. X-ray diffraction (XRD) shows high order satellite peaks and no secondary phases. XRD structural refinement, along with XPS depth profile chemical analysis, reveals that the crystal structure alternates between rhombohedral and in-plane polarized tetragonal phases, effectively corresponding to “artificially created” phase boundaries. SL films have ∼45% and ∼20% higher d_33,f piezoelectric coefficient and dielectric permittivity, respectively, with respect to compositional-gradient-free films of similar thickness, possibly due to enhanced reorientation of electrical dipoles and higher extrinsic contributions due to the motion of the “artificially created” phase boundaries in SL films. Dielectric nonlinear studies indicate a higher amount of extrinsic contributions to the dielectric response in SL and gradient-enhanced films than in conventional films of similar average composition. This processing method provides a simple chemical route to create thin ferroelectric films with enhanced dielectric and piezoelectric properties suitable for a range of miniaturized applications.     

On a non-linear finite element method for piezoelectric structures made of hysteretic ferroelectric ceramics

A simple macroscopic constitutive law for ferroelectric and ferroelastic hysteresis effects of piezoceramics is presented. This constitutive model has been implemented in the public domain finite element code PSU of Stuttgart University (Germany). The fully coupled electro-mechanical boundary value problem for our hysteresis model is solved by incrementation of the loading history. In order to verify the capabilities of our tool, a multilayer-like actuator geometry is analyzed. Concerning the residual stresses present after poling, a tensile stress field perpendicular to the direction of the electrodes can be found in the passive region of the actuator where so-called poling cracks are known to occur. It is the key feature of our finite element tool that it allows the consideration, in structural mechanical analyses, of such phenomena as they are induced by the remanent hysteresis properties of piezoceramics.     

Design,fabrication and properties of 1–3 piezoelectric ceramic composites with varied piezoelectric phase distribution

Here the 1–3 connectivity cement/polymer based piezoelectric composites with varied piezoelectric phase distribution were designed. The dielectric, piezoelectric and electromechanical properties of the composites were studied. The results indicate that the composite with varied distribution of piezoelectric ceramic has large relative permittivity, piezoelectric strain constant and electromechanical coupling coefficient at the thickness vibration mode. The composites with varied distribution of matrix phase have larger piezoelectric voltage constant, smaller mechanical quality factor and acoustic impedance value than those with varied distribution of piezoelectric ceramic phase. The electromechanical coupling property of the composites at the planar vibration mode shows obvious dependence on matrix phase distribution. The novel piezoelectric composites show potential applications in fabricating ultrasonic transducers with specific surface vibration amplitude.     

The fine-grained KNN–LN ceramics densified from nanoparticles obtained by an economical sol–gel route

(1 − x)(K_0.5Na_0.5)NbO₃–xLiNbO₃ ((1 − x)KNN–xLN) nanoparticles with the mean particle size about 20–30 nm have been prepared by an economical sol–gel routes using Nb₂O₅ as Nb source. Due to the high sintering ability of nano-particles, fine-grained KNN–LN lead-free ceramics have been densified at the temperature below 1000 °C. X-ray diffraction analysis indicated that the phase structure of the ceramics changed from orthorhombic to tetragonal at x = 0.08–0.10. When the x reached 0.10 and above, the perovskite structure could not be maintained and the impurity phases of K₃Li₂Nb₅O₁₅ and LiNbO₃ appeared, indicating that x = 0.10 is near the solubility limit. Optimized parameters, such as d₃₃ = 170 pC/N and k_p = 0.40, were achieved in 0.90KNN–0.10LN systems. Due to the merits of fine-grained structure and low sintering temperatures, it will be helpful to the application of KNN–LN materials for lead-free multilayer piezoelectric actuator.