Coupled Efficient Zigzag Finite Element Analysis of Piezoelectric Hybrid Beams under Thermal Loads

A new one-dimensional beam finite element is developed for hybrid piezoelectric beams under thermal load, using a coupled efficient layerwise (zigzag) theory developed recently by the authors. The theory accounts for the layerwise variations of the axial and the transverse displacements while keeping the number of displacement variables independent of the number layers. The beam element has two nodes with four mechanical and a variable number of electric potential degrees of freedom at each node. In the thickness direction, the thermal and the electric fields are approximated as piecewise linear across an arbitrary number of sublayers in a layer. Cubic Hermite interpolation is used for the deflection and electric potentials at the sublayers and linear interpolation is used for the axial displacement and the shear rotation. The thermal field is computed using a consistent six-noded thermal finite element with a quadratic interpolation along longitudinal direction and a linear interpolation along thickness direction. The formulation is validated by comparing the results with the Navier-type solution of the zigzag theory for simply-supported hybrid beams. The element is free from shear locking. The accuracy of the zigzag theory is established by comparing the results of hybrid composite and sandwich beams with the two-dimensional finite element results using ABAQUS for cantilever and clamped-clamped end conditions under different thermal loads. The control of thermal deflection by the application of actuation potential is illustrated. The effects of electric boundary conditions and the pyroelectric effect on the response are discussed.     

The electromechanics of piezoresponse force microscopy for a transversely isotropic piezoelectric medium

Piezoresponse force microscopy (PFM) has emerged as one of the most powerful tools for characterizing and manipulating electromechanical responses of piezoelectric and ferroelectric materials at the nanoscale, yet the interpretation and quantitative analysis of PFM data remains difficult and is not well established. In this paper, we develop a rigorous analysis of PFM using the Hankel integral transform and the effective point charge model, which accounts for the electromechanical coupling of the transversely isotropic piezoelectric medium, the concentrated electric field induced by scanning probe microscopy tip, and the coupling of the electromechanical field at the interface of air and piezoelectric half-space. Using this method, the contact mode is first considered in comparison with the decoupled method, followed by a detailed analysis of the non-contact mode considering the effects of experimental conditions. We note that the decoupled method is only valid for materials with weak piezoelectricity, and the effective piezoelectric coefficient derived from PFM shows nonlinear dependence on the complete set of specimen electromechanical moduli, as well as on the experimental conditions. The analysis thus sheds considerable insight into PFM and could enable determination of intrinsic piezoelectric coefficients through PFM measurement using inverse calculations.     

Growth and piezoelectric properties of Al-substituted langasite-type La3Nb0.5Ga5.5O14 crystals

The influences of aluminum substitution for gallium in the langasite-type La₃Nb_0.5Ga_5.5O₁₄ (LNG) crystals on their growth and electric properties were investigated. Al-substituted LNG (La₃Nb_0.5Ga_5.5−xAl_xO₁₄; LNGAx) single crystals up to the solubility limit x = 0.2 have been grown by the conventional Czochralski technique. The electric properties of the LNGAx crystals were investigated and compared to those of LNG. With Al substitution, the piezoelectric constants, d₁₁ and d₁₄, were slightly higher. The LNGAx crystals showed a temperature dependence of d₁₁ similar to that of the LNG crystal.     

Structure and electrical properties of (1 − x)Bi0.5Na0.5TiO3-xBi0.5K0.5TiO3 ceramics near morphotropic phase boundary

The binary lead-free piezoelectric ceramics with the composition of (1 − x)Bi_0.5Na_0.5TiO₃-xBi_0.5K_0.5TiO₃ were synthesized by conventional mixed-oxide method. The phase structure transformed from rhombohedral to tetragonal phase in the range of 0.16 ≤ x ≤ 0.20. The grain sizes varied with increasing the Bi_0.5K_0.5TiO₃ content. Electrical properties of ceramics are significantly influenced by the Bi_0.5K_0.5TiO₃ content. Two phase transitions at T_t (the temperature at which the phase transition from rhombohedral to tetragonal occurs) and T_c (the Curie temperature) were observed in all the ceramics. Adding Bi_0.5K_0.5TiO₃ content caused the variations of T_t and T_c. A diffuse character was proved by the linear fitting of the modified Curie-Weiss law. Besides, the ceramics with homogeneous microstructure and excellent electrical properties were obtained at x = 0.18 and sintered at 1170 °C. The piezoelectric constant d₃₃, the electromechanical coupling factor K_p and the dielectric constant ?_r reached 144 pC/N, 0.29 and 893, respectively. The dissipation factor tan δ was 0.037.     

Low temperature sintering and properties of piezoelectric PZT-PFW-PMN ceramics with YMnO3 addition

Low temperature sintering of Pb(Zr,Ti)O₃-Pb(Fe_2/3W_1/3)O₃-Pb(Mn_1/3Nb_2/3)O₃ (PZT-PFW-PMN) quaternary piezoelectric ceramics were studied with the use of YMnO₃ as sintering aid. The sintering aid improved the sinterability of PZT-PFW-PMN ceramics due to the effect of YMnO₃ liquid phase. The effects of YMnO₃ contents and sintering temperature on the phase structure, density, dielectric and piezoelectric properties were investigated. The results show that the sintering temperature can be decreased and the electrical properties can be maintained by the YMnO₃ addition. The optimized properties were obtained by doping 0.30 wt.% YMnO₃ and sintering at 1020 °C, which are listed as follows: d₃₃ = 341 pC/N, K_p = 0.57, Q_m = 1393, tan δ = 0.0053, T_c = 304 °C, P_r = 17.13 μC/cm² and E_c = 11.15 kV/cm, which make this system be a promising material for multilayer piezoelectric actuator and transformer applications.     

High sensitivity magnetic sensor consisting of ferromagnetic alloy, piezoelectric ceramic and high-permeability FeCuNbSiB

A high sensitivity magnetoelectric (ME) composite sensor employing a type of ferromagnetic constant-elasticity alloy (FeNi-FACE), piezoelectric Pb(Zr,Ti)O₃ (PZT-8H) and high-permeability FeCuNbSiB (Fe_73.5Cu₁Nb₃Si_13.5B₉) is developed. The FeCuNbSiB ribbon with the high permeability serves as the dynamic driver to increase the effective piezomagnetic coefficient d₃₃ of the FeNi-FACE. At the same time, the FeCuNbSiB/FeNi-FACE/PZT-8H/FeNi-FACE/FeCuNbSiB (FeFPFFe) composite sensor exhibits a higher effective mechanical quality factor (Q_m), which is ∼7.7 times higher than that of Terfenol-D/PZT-8H/Terfenol-D (MPM) sensor. As the ME voltage at resonance is directly proportional to the product of piezomagnetic coefficient and Q_m, a stronger ME effect can be achieved. The experimental results show that the resonance ME voltage coefficient (MEVC) of the FeFPFFe sensor at H_dc = 119 Oe achieves 4.367 V/Oe, which is ∼1.41 times higher than that of FeNi-FACE/PZT-8H/FeNi-FACE (FPF) sensor. Furthermore, ∂VME/∂Hdc for the FeFPFFe sensor achieves ∼22.5 m V/Oe at H_dc = 31 Oe under resonant drive conditions of H_ac = 0.1 Oe, which is ∼20 times higher than that of the previous reported Terfenol-D/Pb(Zr,Ti)O₃/Terfenol-D composite transducer. Thus the FeFPFFe sensor has highly sensitive ac or dc magnetic field sensing.     

Structure, ferroelectric/magnetoelectric properties and leakage current density of (Bi0.85Nd0.15)FeO3 thin films

In this paper, we report on the structure, ferroelectric/magnetoelectric properties and improvement of leakage current density of (Bi_0.85Nd_0.15)FeO₃ (BNFO) thin films deposited on Pt(1 1 1)/Ti/SiO₂/Si substrates from the polymeric precursor method. X-ray patterns and Rietveld refinement indicated that BNFO thin films with a tetragonal structure can be obtained at 500 °C for 2 h in static air. Field emission scanning electron, atomic force and piezoelectric force microscopies showed the microstructure, thickness and domains with polarization-oriented vectors of BNFO thin films. Ferroelectric and magnetoelectric properties are evident by hysteresis loops. The magnetoelectric coefficient measurement was performed to show the magnetoelectric coupling behavior. The maximum magnetoelectric coefficient in the longitudinal direction was close to 12 V/cm Oe. Piezoresponse force microscopy micrographs reveal a polarization reversal with 71° and 180° domain switchings and one striped-domain pattern oriented at 45° besides the presence of some nanodomains with rhombohedral phase involved in a matrix with tetragonal structure. The cluster models illustrated the unipolar strain behavior of BNFO thin films. The leakage current density at 5.0 V is equal to 1.5 × 10⁻¹⁰ A/cm² and the dominant mechanism in the low-leakage current for BNFO thin films was space-charge-limited conduction.     

Effects of Mn substitution on ferro- and piezoelectric properties of Bi0.86Sm0.14FeO3 thin films

The Bi_0.86Sm_0.14FeO₃ (BSFO) and Bi_0.86Sm_0.14Fe_1 − xMn_xO₃ (BSFMO) (x = 0.01, 0.03, 0.05) thin films were deposited on indium tin oxide/glass substrates via a metal organic deposition method. 1 at.% Mn doping leads to an evident reduction of the leakage current in BSFO film. More importantly, the Bi_0.86Sm_0.14Fe_0.99Mn_0.01O₃ film exhibits the lowest coercive field (E_c = 272 kV/cm), the largest remanent polarization (P_r = 53.6 μc/cm²) and the remanent out-of-plane piezoelectric coefficient (d₃₃ = 146 pm/V). However, further increase of Mn doping content results in the deterioration of the charge retaining capability and the piezoelectric properties of the films. The negative influence of high Mn doping contents was discussed based on the structure change and the contribution of irreversible movement of non-180° domain walls in the aged films.     

Effect of MnO doping on the structure, microstructure and electrical properties of the (K,Na,Li)(Nb,Ta,Sb)O3 lead-free piezoceramics

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.     

Direct stamping and capillary flow patterning of solution processable piezoelectric polyvinylidene fluoride films

It is well known that the potential applications of polyvinylidene fluoride (PVDF) mainly come from the piezoelectricity and ferroelectricity of its polar β phase. Thus, we have investigated the effect of different preparation conditions namely evaporation temperature, type of solvent and additive to enhance the β crystal structures of PVDF thin film. Subsequently, facile and direct soft lithography technique; direct stamping and capillary flow were employed to demonstrate good pattern transfer of PVDF thin films. The piezoelectricity of the microstructure was characterized using piezoresponse force microscopy (PFM) where fairly good piezoresponse was obtained without further processing procedures i.e., annealing or applied pressure/electric field. As such, our solution processable and direct patterning of PVDF techniques offer facile and promising route to produce arrays of isolated microstructures with improved piezoelectric functionality.