BaTiO3 nanocubes-Gelatin composites for piezoelectric harvesting: Modeling and experimental study

Flexible composites containing BaTiO₃ nanoparticles into Gelatin bio-polymer matrix were designed and investigated. Following the idea that the electric field concentration in corners/edges at the interfaces between dissimilar materials give rise to enhanced effective permittivity in composites, cuboid-like BaTiO₃ nanoparticles have been employed as nanofillers into Gelatin matrix by using an inexpensive solution-based processing method. As predicted by finite element method simulations developed for cubic-like inclusions into a homogeneous polymer matrix, the experimental permittivity of xBT-(1-x)Gelatin composites increases when increasing the high-permittivity filler addition. For the composition x = 40 wt% (corresponding to 12 vol% BaTiO₃ addition), permittivity reaches ε_r ～15.7 with respect to ε_r ～9.8 of pure Gelatine (measured at 10⁵ Hz), while the average piezoelectric coefficient d₃₃ as determined by piezoelectric force microscopy shows a remarkable increase up to 21 pm/V in composites with x = 40 wt%, in comparison to ～7 pm/V in pure Gelatin. By using the experimentally determined material constants, the simulated piezoelectric voltage output vs. time has shown a similar increase (about a doubling of its amplitude) of the harvesting signal in the composite with x = 40 wt% BT, with respect to one of the polymer matrix, thus demonstrating the beneficial role of embedding BT nanoparticles into the biopolymer for increasing the mechanical harvesting response.     

Ferroelectric to Relaxor Transition in BaTiO3–Bi(Zn2/3Nb1/3)O3 Ceramics

The (1?x)BaTiO₃–xBi(Zn_2/3Nb_1/3)O₃ (x = 0.01–0.30) ceramics were synthesized by solid‐state reactions. The solubility limit was determined to be x = 0.20. A systematic structural transition from a tetragonal phase (x ≤ 0.034), to a mixture of tetragonal and rhombohedral phases (0.038 ≤ x ≤ 0.20), and finally to a pseudocubic phase (x ≥ 0.22) at room temperature was identified. Dielectric measurement revealed a ferroelectric (x ≤ 0.04) to relaxor (x ≥ 0.06) transition with permittivity peak broadening and flattening, which was further verified by Raman spectroscopy and differential scanning calorimetry (DSC). Activation energies obtained from the Vogel–Fulcher model displayed an increasing trend from ~0.03 eV for x ~ 0.05, to unusually high values (>0.20 eV) for the compositions with x ≥ 0.15. With the increase in Bi(Zn_2/3Nb_1/3)O₃ content, the polarization hysteresis demonstrated a tendency from high nonlinearity to sublinearity coupled with the reduction in remnant polarization and coervice field. The deconvolution of the irreversible/reversible polarization contribution was enabled by first‐order reversal curve distributions, which indicates that the decreasing polarization nonlinearity with the increase in Bi(Zn_2/3Nb_1/3)O₃ concentration could be related with the change from the ferroelectric domain and domain wall contributions to the weakly coupled relaxor behaviors.     

Effect of BiMO3 (M=Al,In, Y,Sm, Nd,and La) doping on the dielectric properties of BaTiO3 ceramics

In this study, in order to enhance the energy storage density, 10% BiMO₃ doping is performed in BaTiO₃ ceramics (M=Al, In, Y, Sm, Nd, La) by a traditional solid-state method. The effects of different M³⁺ radii on the structural characteristics, dielectric properties, and energy storage are investigated systematically. The locations of the M-ions gradually shift from B-site substitutions to A-site substitutions with the increase in the ionic radius, which affect the structural characteristics and the dielectric properties. When 80<R_M3+<95.5 pm, the ceramic has a cubic phase which shows the highest energy density; while out of this range, the dielectric properties of the ceramics are degraded. Specially, the change rate of permittivity of the Sm substituted composition reaches 70% at 100 kV/cm, which might be good for high frequency tunable device application. Typically, combined with the suppression of nonlinearity, polarization maximum (P_m) and remnant polarization (P_r), 0.9BaTiO₃–0.1BiInO₃ exhibits the maximum energy density of 0.753 J/cm³ and the highest energy efficiency of 89.4%, which exhibits slim P-E hysteresis loops for energy storage applications.     

Effect of repeated composite sol infiltrations on the dielectric and piezoelectric properties of a Bi0.5(Na0.82K0.18)0.5TiO3 lead free thick film

Bi_0.5(Na_0.82K_0.18)_0.5TiO₃ lead free thick films have been produced using a combination of screen printing and subsequent infiltration of corresponding composite sol. Their structure, dielectric, ferroelectric and piezoelectric properties were investigated with variation in the number of composite sol infiltrations and the nanopowder loading in composite sol. Dielectric constant, remanent polarization, and piezoelectric coefficient have been shown to increase with increasing numbers of composite sol infiltration. Dielectric and ferroelectric properties of the thick films are found to be strongly dependent on the powder concentration of composite sols. The resulting 40 μm thick films infiltrated with 1.5 g/ml composite sols have maximum relative permittivity of 569 (at 10 kHz), remanent polarization of 21.3 μC/cm², coercive field of 80 kV/cm, and longitudinal effective piezoelectric coefficient d_33eff of 109 pm/V. The performance of these lead free piezoelectric thick films is comparable to the corresponding bulk ceramics.     

Low‐temperature sintering and enhanced piezoelectric properties of random and textured PIN–PMN–PT ceramics with Li2CO3

Low‐temperature sintered random and textured 36PIN–30PMN–34PT piezoelectric ceramics were successfully synthesized at a temperature as low as 950°C using Li₂CO₃ as sintering aids. The effects of Li₂CO₃ addition on microstructure, dielectric, ferroelectric, and piezoelectric properties in 36PIN–30PMN–34PT ternary system were systematically investigated. The results showed that the grain size of the specimens increased with the addition of sintering aids. The optimum properties for the random samples were obtained at 0.5 wt% Li₂CO₃ addition, with piezoelectric constant d₃₃ of 450 pC/N, planar electromechanical coupling coefficient k_p of 49%, peak permittivity ε_max of 25 612, remanent polarization P_r of 36.3 μC/cm². Moreover, the low‐temperature‐sintered textured samples at 0.5 wt% Li₂CO₃ addition exhibited a higher piezoelectric constant d₃₃ of 560 pC/N. These results indicated that the low‐temperature‐sintered 36PIN–30PMN–34PT piezoelectric ceramics were very promising candidates for the multilayer piezoelectric applications.     

Improved thermal stability of ferro/piezo-electric properties of Mn-doped Pb(In1/2Nb1/2)O3-PbTiO3 ceramics

Thermal stability of piezo-/ferro-electric properties of ferroelectrics is important for the devices working at elevated temperature. A study on thermal stability of ferroelectrics will be greatly helpful for future applications. In this work, thermal behaviors of electrical properties were studied in Mn-doped Pb(In_1/2Nb_1/2)O₃-PbTiO₃ (PINT) ceramics. The ferroelectric hysteresis loops of Mn-doped samples change anomalously with increasing temperature compared with the virgin sample. Remnant polarization of PINT ceramics with high manganese content (x?≥?0.04) exhibits increase trend as temperature increasing, leading to a negative electrocaloric effect which was reported to be beneficial to improving the cooling efficiency. For Mn-doped PINT ceramics, the reduction rate of coercive field reaches a relatively low value of 3%, indicating outstanding ability of depolarization resistance. PINT ceramics with proper dopant concentration show improved aging resistance and thermal stability of piezoelectric property after annealed. Out-of-plane domain configurations show different features at room temperature and elevated temperatures.     

Room temperature phase superposition as origin of enhanced functional properties in BaTiO3 - based ceramics

BaSn_xTi_1-xO₃ (x = 0, 0.05) ceramics with orthorhombic/tetragonal phases at room temperature were comparatively investigated to understand the role of phase composition on their functional properties. With respect to the values of BaTiO₃, the switching polarization, permittivity peak, tunability and piezoelectric coefficients are enhanced by doping with 5 % Sn onto Ti⁴⁺ sites. The orthorhombic polymorph amount is larger in the doped ceramic and explains its higher switching polarization. High field poling favors the orthorhombic phase in both compositions; this polymorph becomes predominant in the BaSn_0.05Ti_0.95O₃ ceramic. Landau-based calculations developed for ceramics with randomly oriented grains predicted the stability of variable amounts of orthorhombic/tetragonal phases around room temperature and explain the field-induced predominant orthorhombic state, mostly in BaSn_0.05Ti_0.95O₃. Due to the twelve allowed spontaneous polarization directions, the orthorhombic state is responsible for the enhanced polarization, tunability and piezoelectric properties with respect to the tetragonal state with six polarization possible orientations.     

Effects of Fe2O3 doping on the electrical properties of Na0.47Bi0.47Ba0.06TiO3 lead-free ceramics

The Na_0.47Bi_0.47Ba_0.06Ti_1-xFe_xO_3-Δ lead-free piezoelectric ceramics (BNBT-100xFe, x?=?0, 0.01, 0.02, 0.03) were synthesized by using the solid-state reaction technique. X-ray powder diffraction patterns demonstrate that the doping Fe₂O₃ has totally diffused into the crystal lattice of the ceramics and form a pure perovskite structure. Enhanced piezoelectric property is obtained at x?=?0.01, which is reflected on the enhanced remnant polarization (P_r) and a giant piezoelectric constant (d₃₃) up to 168 pC/N. The increasing ferroelectric-to-relaxor phase transition temperature (T_F-R) on dielectric permittivity curves suggest the enhanced ferroelectric characteristics with increasing the Fe³⁺ content. By using the complex ac impedance analysis, the grain, grain boundary and electrode effects are all detected at the appreciate composition. The resistivity behavior of the samples is sensitive to the doping Fe³⁺ concentration, and additionally, the oxygen vacancies play an important role in this characteristic.     

Tailoring the Piezoelectric and Relaxor Properties of (Bi1/2Na1/2)TiO3–BaTiO3 via Zirconium Doping

This article details the influence of zirconium doping on the piezoelectric properties and relaxor characteristics of 94(Bi_1/2Na_1/2)TiO₃–6Ba(Zr_xTi_1?x)O₃ (BNT–6BZT) bulk ceramics. Neutron diffraction measurements of BNT–6BZT doped with 0%–15% Zr revealed an electric‐field‐induced transition of the average crystal structure from pseudo‐cubic to rhombohedral/tetragonal symmetries across the entire compositional range. The addition of Zr up to 10% stabilizes this transition, resulting in saturated polarization hysteresis loops with a maximum polarization of 40 μC/cm² at 5.5 kV/mm, while corresponding strain hysteresis measurements yield a maximum strain of 0.3%. With further Zr addition, the ferroelectric order is progressively destabilized and typical relaxor characteristics such as double peaks in the current density loops are observed. In the strain hysteresis, this destabilization leads to an increase of the maximum strain by 0.05%. These changes to the physical behavior caused by Zr addition are consistent with a reduction of the transition temperature T_F‐R, above which the field‐induced transformation from the relaxor to ferroelectric state becomes reversible.     

Enhanced dielectric and piezoelectric properties in potassium sodium niobate/polyvinylidene fluoride composites using nano-silicon carbide as an additive

Piezoelectric materials are an indispensable part of modern life. Yet the existing environmental issues with conventional lead-based piezoelectrics has motivated scientist to develop novel substitutes including lead-free piezoelectric polymer composites. Following this path, the present research has focused on the fabrication of ternary composites of Polyvinylidene fluoride (PVDF)/Potassium Sodium Niobate (KNN)/nano-Silicon carbide (SiC) via hot compression molding and studying the effect of additives on the PVDF structure and the electrical properties of the composite. The obtained scanning electron micrographs and density measurements showed that the fabrication method provided dense samples. The activated polarization phenomena in the prepared samples enhanced dielectric permittivity and dielectric loss at a constant frequency with increasing KNN and SiC contents. Besides the expected dipole polarization, the presence of interfaces in the composites gave rise to the Maxwell–Wagner–Sillars effect and its corresponding polarization phenomenon. The semiconductive nature of SiC also promoted space charge polarization. However, these properties were frequency-dependent because the first two polarization mechanisms are deactivated at high frequencies. XRD patterns showed that SiC addition can alter the primary crystalline structure of PVDF and promote β-phase formation in the poled samples. Piezoelectric measurements confirmed the significant role of SiC addition to PVDF-KNN composites. The most significant increase in the piezoelectric properties was observed in PVDF-60KNN-1SiC, with a 183% increase in d₃₃ value. The PVDF-80KNN-1SiC had the highest d₃₃ value of 30.5 pC/N. It also had the best piezoelectric voltage coefficient and hence the highest figure of merit. Higher SiC contents restrict the efficiency of poling by forming a conductive path across the sample which would deteriorate the piezoelectric performance of the material. The present findings show that PVDF-KNN-SiC composites can be considered as a potential flexible piezoelectric material for future applications.     

Piezoelectric performance of 0.5BaZr0.2Ti0.8O3-0.5Ba1-xCaxTiO3 at triple phase point

0.5BaZr_0.2Ti_0.8O₃-0.5Ba_1-xCa_xTiO₃ ceramic samples with x = 15–35% have been fabricated to investigate the composition-driven phase evolution, ferroelectric, and piezoelectric properties. X-ray diffraction and temperature-dependent permittivity studies reveal the structural phase transition from the rhombohedral (R) to R + orthorhombic (O) and then O + tetragonal (T) having a tricritical triple phase points consisting of the R + O + T at x = 29.6%. The average grain size tends to increase with x but there is an exception of reducing grain size for x = 29.6%. The triple phase point displays the outstanding properties, such as minimum relaxation time (τ = 6.4 ms), large piezoelectric response (d₃₃ = 543 pC/N), high saturation polarization (P_S = 16.5 μC/cm²), small coercive field (E_c = 0.6 kV/cm), and high dielectric permittivity, over 8700 peaking at 21,765. These parameters reduce drastically at the O/R and O/T phase boundaries. Our studies indicate the important role of multiphase coexistence for enhancing the piezoelectric properties.     

Temperature dependent,large electromechanical strain in Nd-doped BiFeO3-BaTiO3 lead-free ceramics

Lead-free piezoceramics with the composition 0.7(Bi_1-xNd_x)FeO₃-0.3BaTiO₃+0.1 wt% MnO₂ (BNxF-BT) were prepared using a conventional solid state route. X-ray diffraction and temperature dependent permittivity measurements indicated a transition from a composition lying at a morphotropic phase boundary (MPB) to a pseudocubic phase as a function of Nd concentration. The highest maximum strain (S_max ∼ 0.2% at 60 kV/cm) and effective piezoelectric coefficient (d₃₃* = 333 pm/V) were obtained at room temperature for the composition BN0.02F-BT. The decrease in remanent polarization (P_r) and Berlincourt d₃₃ with increase in Nd concentration can be attributed to the coexistence of ferroelectric and relaxor phases. In-situ polarisation and strain measurements revealed an increase in P_r and d₃₃* with temperature and a reduction in the coercive field E_C. Presumably this behavior is due to a combination of thermally activated domain wall motion and lowering of the activation energy for a field induced relaxor-ferroelectric transition, as the Curie maximum is approached.     

Influence of B‐Site Disorder on the Properties of Unpoled Bi1/2Na1/2TiO3‐0.06Ba(ZrxTi1‐x)O3 Piezoceramics

The influence of B‐site disorder on the dielectric, microstructural, and structural characteristics of unpoled, lead‐free (Bi_1/2Na_1/2)TiO₃‐0.06Ba(Zr_xTi_1‐x)O₃ piezoelectric ceramics with x = 0.02, 0.10, and 0.15 was investigated. The low and medium doping level introduced a stabilization of polar nanoregions reflected in the shift of the dispersive permittivity anomalies to higher temperatures and the development of lamellar rhombohedral domains embedded in the prevalent tetragonal nanodomain matrix. For higher Zr level, the regions of lamellar domains remain, but the dielectric characteristics indicate a reduction in the previous stabilization effect. This behavior is rationalized by a reduction in the correlation length due to the increasing amount of nonpolar sample volume with increasing Zr addition.     

Broadband dielectric properties of multiwalled carbon nanotube/polystyrene composites

This study investigates the dielectric properties of multiwalled carbon nanotube (MWCNT)/polystyrene (PS) composites over the broadband frequency range, i.e., 10^?1 to 10⁶ Hz. The results showed that the real permittivity and imaginary permittivity increased remarkably with increased MWCNT concentration. For instance, at 100 Hz, the real permittivity and imaginary permittivity of the pristine PS was 2.71 and 0.01, respectively, which increased to 5.22 × 10⁴ and 3.28 × 10⁷ at 3.50 wt%, respectively. The increase in the real permittivity was related to the formation of a large number of nanocapacitor structures, i.e., MWCNTs as nanoelectrodes and polymer matrix as dielectric material, i.e., interfacial polarization. The increase in the imaginary permittivity with MWCNT loading was attributed greater number of dissipating charges, enhanced conductive network formation, and boosted polarization loss arising from interfacial polarization. It was also observed that the real and imaginary permittivities were frequency independent in the insulative region, whereas they decreased drastically with frequency in the conductive region. The descending trend of real permittivity with frequency in the conductive region was related to charge polarization relaxation, whereas the reduction in imaginary permittivity with frequency was attributed to lower Ohmic loss and polarization loss. POLYM. ENG. SCI., 55:173–179, 2015. © 2014 Society of Plastics Engineers     

Quenching-circumvented ergodicity in relaxor Na1/2Bi1/2TiO3-BaTiO3-K0.5Na0.5NbO3

Quenching alkaline bismuth titanates from sintering temperatures results in increased lattice distortion and consequently higher depolarization temperature. This work investigates the influence of quenching on the ergodicity of relaxor Na_1/2Bi_1/2TiO₃-BaTiO₃-K_0.5Na_0.5NbO₃. A distinct departure from ergodicity is evidenced from the increase in remanent polarization and the absence of frequency dispersion in the permittivity response of poled samples. Further, the samples exhibit enhanced negative strain upon application of electric field, indicating proclivity towards correlated polar nanoregions, corroborated by the enhanced tetragonal distortion. As a result, ergodic relaxor Na_1/2Bi_1/2TiO₃-6BaTiO₃-3K_0.5Na_0.5NbO₃ exhibits a depolarization temperature of 85°C with a 60% increase in remanent polarization and approximately a threefold increase in remanent strain upon quenching. Quenching-induced changes in the local environment of Na⁺ and Bi³⁺ cations hinder the development of ergodicity promoted by the A-site disorder. These results provide new insight into tailoring ergodicity of relaxor ferroelectrics.     

Dielectric,magnetic and magnetoelectric properties of Ni0.5Zn0.5Fe2O4+Pb(Zr0.48Ti0.52)O3 composite ceramics

Magnetoelectric composite ceramics of spinel ferrite Ni_0.5Zn_0.5Fe₂O₄ (NZFO) with high magnetic permeability and tetragonal perovskite Pb(Zr_0.48Ti_0.52)O₃ (PZT) with high piezoelectric constant were synthesized by common solid state reaction method. XRD and SEM showed that high dense composite ceramics without any foreign phases were obtained. The ceramics showed excellent dielectric and magnetic properties, which were stable in a large frequency range. The dielectric peak became wider with the ferrite content in the permittivity spectrum with temperature. With the increase in the ferrite content, the magnetic Curie temperature shifted to higher temperature and closed to that of the pure ferrite. In addition, the magnetoelectric coefficient enhanced as the increase in the ferrite content. The properties of the composite ceramics could be adjusted by the ferrite content. These research results provided a powerful experimental basis for the sensor and transducer in microelectronic and microwave devices.     

Evolution of Relaxor Behavior in Multiferroic Pb(Fe2/3W1/3)O3-BiFeO3 Solid Solution of Complex Perovskite Structure

Mutiferroic materials like bismuth ferrite BiFeO₃ have attracted much interest in the last decade due to their promising potential for such applications as spintronics and magnetoelectric data storage devices. On the other hand, relaxor ferroelectrics have been intensively studied for their complex structures with quenched disorder and polar nanoregions which play an important role in their outstanding piezoelectric performance. Much less studied are the single-phase multiferroics that exhibit ferroelectric and/or magnetic relaxor behavior and the correlation between their structure and intricate magneto-electric interactions. In this work, we investigate the evolution of the structure and relaxor behavior in the solid solution between the complex perovskite multirelaxor Pb(Fe_2/3W_1/3)O₃ [PFW] and canonical multiferroic BiFeO₃ [BFO], (1-x)PFW-xBFO (with a solubility limit of x = 0.30). The temperature dependences of the dielectric permittivity and loss tangent measured in the frequency range from 100 Hz to 1 MHz indicate characteristic relaxor ferroelectric properties for compositions of x ≤ 0.15, with a frequency-dependent dielectric permittivity peak and its temperature, T_m, satisfying the Vogel-Fulcher law. Detailed studies of the evolution of the relaxor behavior with composition reveal that T_m decreases firstly with a small amount (x = 0.05) of BFO substitution and then increases with further increase of BFO concentration. The degree of relaxor character, as defined by ΔT_m [T_m (1 MHz) - T_m (100 Hz)], increases monotonously with increasing BFO content, signifying an enhancement of relaxor behavior with BFO substitution, which is confirmed by the Lorenz-type quadratic variation of the static permittivity. A temperature - composition phase diagram is constructed in terms of the characteristic Burns temperature (T_B) and freezing temperature (T_f), which delimits a paraelectric state (PE) above T_B, a non-ergotic relaxor state (NR) below T_f, and an ergotic relaxor state (ER) in between. The observed enhancement of relaxor behavior is explained by an increase in the number and size distribution of polar nanoregions in the ER phase, resulting from increased compositional and charge disorders as a result of BFO substitution. The evolution of relaxor behavior and its microscopic mechanisms studied in this work are insightful for a better understanding the multirelaxor properties in multiferroics. Moreover, further substitution of BFO (x ≥ 0.2) flattens the permittivity curves and leads to a temperature-stable variation of high dielectric constant (≈ 10³) in a wide temperature range, making the PFW-BFO solid solution attractive for such applications as high energy density capacitors.     

Effects of Sm-substitution on dielectric,ferroelectric, and piezoelectric properties of 0.36(Bi1-xSmx)ScO3-0.64PbTiO3 ceramics

Dielectric, ferroelectric, and piezoelectric properties of 0.36(Bi_1-xSm_x)ScO₃-0.64PbTiO₃ (BSPT-xSm) ceramics were investigated to assess effects of Sm-substitution on 0.36BiScO₃-0.64PbTiO₃ for high temperature piezoelectric device application. Optimal sintering was achieved at 1200°C when the BSPT-xSm ceramics were fully densified and crystallized with a perovskite structure without any secondary phase. The substitution of Bi³⁺ with Sm resulted in degradation of rhombohedral side in BSPT-xSm ceramics having morphotropic phase boundary. In addition, variations of grain size and ferroelectric behavior after Sm-substitution were insignificant. However, dielectric constant (ε^T₃₃/ε₀) was significantly enhanced with an increasing of amount of Sm to 5%. Although a slight decrease of relative density in case of x exceeding 3% led to deterioration of piezoelectric values of d₃₃, k_p, and d₃₃*, the BSPT-3%Sm ceramic exhibited excellent values of d₃₃ of 628 pC/N, k_p of 62.4%, and d₃₃* of 718 pm/V at 4.5 kV/mm, along with a high ferroelectric transition temperature of 421°C. The highly increased diffusion coefficient of 1.909 also implies that the Sm-substitution contributed to relaxor-like ferroelectric behavior of BSPT ceramics.     

Clamping of ferroelectric PVDF to enhance the electromechanical performance of a 1–3 PMN-PT/PVDF piezoelectric composite

A group of 1–3 type piezoelectric Pb (Mg_1/3Nb_2/3)O₃-PbTiO₃/polyvinylidene fluoride (PMN-PT/PVDF) composite sheets are prepared using a complex two-step hot-pressing method. Then the molecular structure model of piezoelectric materials and an inverse piezoelectric simulation of the composites are performed to express the horizontal compression, indicating the clamping activity of ferroelectric PVDF on PMN-PT. As such, this composite sheet possesses a high dielectric permittivity (ε_r) of 560 at 100 Hz for its compacted connecting of two phases. After polarization, a very large piezoelectric coefficient (d₃₃) of 1125 pC/N and a considerable electromechanical coupling factor (k_t) of 0.43 is obtained in PMN-PT/PVDF sheet with a proper aspect ratio of 1.4 and a thickness of 2.1 mm, further indicating that promoting effect of PVDF matrix on the strain in Z-direction of PMN-PT. The result shows that ferroelectric PVDF serving as polymer matrix favors the electromechanical coupling effect, and may provide a prospect of the potential application of PMN-PT/PVDF composite in sensor or transistor for matrix ultrasonic probes.