Enhanced piezoelectric and mechanical properties of ZnO whiskers and Sb2O3 co-modified lead zirconate titanate composites

ZnO whiskers and Sb₂O₃ co-modified lead zirconate titanate (denoted as PZT/ZnO_w/Sb₂O₃) piezoelectric composites were fabricated using a solid state sintering technique. The characteristic diffraction peaks of the PZT perovskite and ZnO phases were identified from all the composites, suggesting the retention of these individual phases. The grain size of PZT was found to be reduced with Sb₂O₃ addition. A high relative density of 96.5%-99.1% was achieved in PZT co-doped with ZnO_w and Sb₂O₃. Both the piezoelectric and mechanical properties of the PZT/ZnO_w/Sb₂O₃ composites showed significant improvement over the monolithic PZT. The intrinsic effects of ZnO_w and Sb₂O₃ on the electrical and mechanical properties of the PZT/ZnO_w/Sb₂O₃ composites were discussed.     

Effects of Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> addition on the microstructure,electrical, and mechanical properties of PZT/ZnO nanowhisker piezoelectric composites

Nb₂O₅-modified PZT/ZnO nanowhisker (denoted as PZT/ZnO_w–Nb₂O₅) piezoelectric composites were prepared by a solid state sintering technique. Effects of Nb₂O₅ addition on the microstructure, electrical, and mechanical properties of the PZT/ZnO_w composites were investigated. With increasing Nb₂O₅ content, the grain size of the composites was reduced and the fracture mode changed from intergranular to intragranular gradually. Compared with the PZT/ZnO_w composites, the dielectric, piezoelectric, and ferroelectric properties of the PZT/ZnO_w–Nb₂O₅ composites were improved significantly, while mechanical properties were enhanced slightly. The optimum electrical and mechanical properties were achieved for the PZT/ZnO_w composites modified with 0.75 wt% Nb₂O₅ sintered at 1150 °C, with dielectric permittivity ε_r, piezoelectric coefficient d ₃₃, planar electromechanical coupling k _p, remnant polarization P _r, fracture toughness K _IC, and flexural strength σ_f being on the order of 4930, 600 pC/N, 0.63, 29.2 μC/cm², 1.56 MPa m^1/2 and 130 MPa, respectively. The Nb₂O₅-modified PZT/ZnO_w piezoelectric composites, with comparable electrical properties and improved mechanical properties than those of commercial PZT-5H ceramics, are promising candidates for further applications.     

Synthesis and electrical properties of Pb(Zr0.52Ti0.48)O3 thick films embedded with ZnO nanoneedles prepared by the hybrid sol–gel method

Pb(Zr_0.52Ti_0.48)O₃ thick films embedded with ZnO nanoneedles (PZT–ZnO_n) were successfully prepared on Pt/Cr/SiO₂/Si substrates by the hybrid sol–gel method via spin-coating ZnO_n suspension and lead zirconate titanate (PZT) sol. To control the orientation of the films, a PbTiO₃ (PT) layer was first deposited as a seed layer. Effects of annealing method and ZnO_n contents on the corresponding orientation and crystallization of PZT–ZnO_n films were investigated by XRD and SEM. The results show that all the PZT–ZnO_n composite thick films have pure perovskite structure and high-quality film surface. The dielectric and ferroelectric properties of the PZT–ZnO_n films are close to the PZT films, and have a little decrease with the increasing of the ZnO_n contents.     

Effects of VC additives on densification and elastic and mechanical properties of hot-pressed ZrB<Subscript>2</Subscript>–SiC composites

In this study, highly dense ZrB₂-20 vol% SiC composites with 3–10 wt% VC additives were prepared by hot-pressing at 1750 °C for 1 h under a pressure of 20 MPa in a vacuum. The densification behavior and elastic and mechanical properties of the obtained composites were examined, and the effect of the VC content on the densification and the properties is analyzed. The addition of VC promotes the activation of densification mechanism at a lower temperature and inhibits the growth of ZrB₂ and SiC grains during the sintering. In addition, the elastic moduli, hardness and fracture toughness that measured in the obtained composites are constant and independent of the VC content, with a shear modulus of ~ 220 GPa, Young’s modulus of ~ 500 GPa, hardness of ~ 20 GPa and fracture toughness of ~ 4.4 MPa m^1/2. On the other hand, the flexural strength of the composites decreased as the VC content increased from 3 to 7 wt% and then it increased with further increasing the VC content to 10 wt%, with strength values of 620–770 MPa.     

Structure and electrical properties of MnO doped (Ba<Subscript>0.96</Subscript>Ca<Subscript>0.04</Subscript>)(Ti<Subscript>0.92</Subscript>Sn<Subscript>0.08</Subscript>)O<Subscript>3</Subscript> lead free ceramics

In this work, (Ba_0.96Ca_0.04)(Ti_0.92Sn_0.08)O₃–xmol MnO (BCTS–xMn) lead-free piezoelectric ceramics were fabricated by the conventional solid-state technique. The composition dependence (0 ≤ x ≤ 3.0 %) of the microstructure, phase structure, and electrical properties was systematically investigated. An O–T phase structure was obtained in all ceramics, and the sintering behavior of the BCTS ceramics was gradually improved by doping MnO content. In addition, the relationship between poling temperature and piezoelectric activity was discussed. The ceramics with x = 1.5 % sintering at temperature of 1330 °C demonstrated an optimum electrical behavior: d ₃₃ ~ 475 pC/N, k _p ~ 50 %, ε _r ~ 4060, tanδ ~ 0.4 %, P _r ~ 10.3 μC/cm², E _c ~ 1.35 kV/mm, T _C ~ 82 °C, strain ~0.114 % and \(d_{33}^{*}\) ~ 525 pm/V. As a result, we achieved a preferable electric performance in BaTiO₃-based ceramics with lower sintering temperature, suggesting that the BCTS–xMn material system is a promising candidate for lead-free piezoelectric ceramics.     

Phase transition and piezoelectric properties of (1−x)(K0.42Na0.58)(Nb0.96Sb0.04)O3–x(Bi0.5Na0.5)0.90Mg0.10ZrO3 lead-free ceramics

(1?x)(K_0.42Na_0.58)(Nb_0.96Sb_0.04)O₃–x(Bi_0.5Na_0.5)_0.90Mg_0.10ZrO₃ [(1?x)KNNS–xBNMZ] lead-free ceramics have been prepared by the normal sintering, and effects of BNMZ content on their phase structure, microstructure, and electrical properties have been systematically investigated. These ceramics with 0.045 ≤ x ≤ 0.05 possess a rhombohedral–tetragonal (R–T) phase boundary, as confirmed by the temperature dependence of dielectric properties and X-ray diffraction patterns. The grain size of the ceramics first increases and then decreases as the BNMZ content increases, and the ceramic with x = 0.06 possesses much smaller grains (<1 μm), resulting in the abnormal electrical and phase transition behavior. In addition, the Mg²⁺ was homogenously distributed in the ceramic matrixes. These ceramics with R–T phase boundary show enhanced dielectric, ferroelectric, and piezoelectric properties as compared with a pure KNN, and optimum electrical properties (e.g., P _r ~ 16.23 μC/cm², E _C ~ 7.58 kV/cm, ε _r ~ 2,663, tan δ ~ 0.034, d ₃₃ ~ 434 pC/N, k _p ~ 0.47, and T _C ~ 244 °C) were found in the ceramic with x = 0.0475. We believe that the (1?x)KNNS–xBNMZ ceramic is a promising candidate for lead-free piezoelectric devices.     

Bismuth sodium titanate based lead-free ceramic/epoxy 1–3 composites: fabrication and electromechanical properties

The 1–3 piezocomposites based on 0.96Bi_0.5(Na_0.84K_0.16)_0.5TiO₃–0.04SrTiO₃ (BNKT–ST) were fabricated by a modified dice-fill method. Electro-mechanical properties of the composites as a function of the ceramic volume fraction (v) were measured and compared with theoretical values as well as with those of monolithic ceramics. The as-prepared piezocomposite with v = 0.276 showed a clear single thickness mode with a relatively high resonance frequency of more than 2 MHz, together with a relatively high piezoelectric strain constant (d ₃₃ ~ 104 pC/N), a high thickness coupling coefficient (k _t  ~ 0.547), low acoustic impedance (Z ~ 9 Mrayls) and a large piezoelectric voltage coefficient (g ₃₃ ~ 91.5 × 10^?3 m²/C). From the practical application point of view, these promising results indicate that the BNKT–ST ceramic/epoxy 1–3 composite has great potential to be used in biomedical ultrasonic transducers as well as nondestructive evaluations.     

Piezoelectric,ferroelectric and mechanical properties of lead zirconate titanate/zinc oxide nanowhisker ceramics

New lead zirconate titanate/zinc oxide nanowhisker (PZT/ZnO_w) ceramics were fabricated by a conventional solid state processing and their structures, piezoelectric, ferroelectric and mechanical properties were studied. Both the PZT perovskite and ZnO phases can be observed from the X-ray diffraction patterns. The grain size of ceramics is reduced due to the ZnO_w addition. The incorporation of ZnO_w into the PZT ceramics improves the strength and toughness, while deteriorates the piezoelectric and ferroelectric properties. For the PZT/ZnO_w ceramics with 1–2 wt% ZnO_w, the mechanical properties become optimum, meanwhile maintain good piezoelectric and ferroelectric properties: σ _c = 376–484 MPa, σ _f = 115–121 MPa, K _IC = 1.41–1.54 MPa m^1/2, d ₃₃ = 442–490 pC/N, k _p = 0.54–0.55, ε _r = 3,322–3,980, Q _m = 99–101, tanδ = 1.6%–1.7%, P _r = 21.5–26.9 μC/cm² and E _c = 8.1–8.6 kV/cm.     

High piezoelectric coefficient of Ba0.85Ca0.15Ti0.90Zr0.10O3−Sr(Cu1/3Ta2/3)O3 ceramics

The (Ba_0.85Ca_0.15) (Zr_0.1Ti_0.9)O₃ ? x   wt% Sr(Cu_1/3Ta_2/3)O₃ [BCZT ? x  wt% SCT, x = 0–0.3] lead-free ceramics were prepared by the conventional solid-state method. The phase structure was investigated by X-ray diffraction. The results show that only a tetragonal phase is observed in these ceramics. The sintering behavior of BCZT ceramics is also improved by using SCT as a sintering aid. The ceramic with x  = 0.2 wt% SCT demonstrates good piezoelectric properties:d₃₃ ~ 577 pC/N and k_p ~ 59.1 %, Furthermore, the Curie temperature of the ceramics also increases and reaches 97 °C.     

Preparation and piezoelectric properties of CuO-doped (Na0.5K0.5)NbO3 ceramics by the citrate precursor method

A low-cost citrate so-gel route was investigated to synthesize nano-sized crystalline powders (<100 nm) of 1 mol% CuO modified (Na_0.5K_0.5)NbO₃ compositions. It was found that amorphous gels can be transformed into crystallite powders with single-phase perovskite structure when calcined at 500?C600 °C for 3 h. The transmission electron microscopy observation showed that the particles are column-like and well dispersed, depending on the calcination condition. The as-pressed samples exhibit improved densification behavior and finer grain morphology after sintering. Electrical properties of the samples sintered at 1,060 °C are as follows: dielectric constant ?? _r  = 605, piezoelectric constant d ₃₃ ~ 117 pC/N, planar electromechanical coupling factor k _p  ~ 0.38 and mechanical quality factor Q _m  ~ 725.     

Co-firing preparation and properties of piezoelectric ceramic/structural ceramics layered composites

Pb(Zr, Ti)O₃(PZT)-based piezoelectric ceramics and Al₂O₃-based structural ceramics were cast and co-fired to prepare a layered piezoelectric ceramic/structural ceramic composite. Considering the significant differences in sintering characteristics of PZT- and Al₂O_3-based ceramics, control of the sintering temperature and the dependence of the linear shrinkage on the solid content of the tape-casting films were systematically conducted at first. The sintering density and the interface bonding properties of the prepared composites were then investigated. The results of electrical and mechanical properties of the composite ceramics indicate: By using sintering aids, Al₂O₃ ceramic could be fully densified and co-fired with PZT ceramic at 1150 °C. Shrinkage matching during sintering was achieved by adjusting the solid contents to 45 vol.% and 65 vol.% for PZT and alumina tape-casting films. In the layered composites, Al₂O₃ structural ceramic presents an excellent mechanical property with HV hardness of 667, while the PZT functional ceramic presents d₃₃, ε_r and tanδ of 259 pC/N, 965 and 0.37%, respectively.

     

Effect of aged binder on piezoelectric properties of cement-based piezoelectric composites

Age-dependent piezoelectric properties of cement piezoelectric composites containing cement-based binder and 50 vol. % PZT piezoelectric inclusions are conducted. The effect of binder with 10 to 50 % cement replaced by slag and fly ash is investigated. Specimens are polarized by 1.5 kV/mm for 30 min when the curing time reaches 7, 28 and 56 days, respectively. Experimental values are measured daily till 120 days after the polarization. Prior to polarization, dielectric loss needs to be less than 0.73 to guarantee the feasibility of polarization. Piezoelectric properties including d ₃₃, g ₃₃ and ?_r are age-dependent unless the age is higher than 60 days after the polarization. The electromechanical coupling coefficient κ_t is independent of the ages. The curing time shows less efficient to piezoelectric properties while hydration reaction is completed. 20 vol. % cement replaced by slag or fly ash provides optimum d ₃₃ and g _33. Compared with slag replacement, fly ash replacement can diminish ?_r, but increase κ_t. In addition, a modified equation to calculate the dielectric constant of PZT/cement composites is also proposed.     

Structure and piezoelectric properties of K0.5Na0.5NbO3–AlFeO3 lead-free ceramics by using AlFeO3 as a sintering aid

The (1 ? x)K_0.5Na_0.5NbO₃–xAlFeO₃ ((1 ? x)KNN–xAF) (x = 0.01–0.08) lead-free piezoelectric ceramics were prepared at low temperature of 1,000 °C by conventional ceramic processing. And AF was used as a sintering aid in order to improve the sintering behavior of KNN. The effect of AF addition on the microstructure, dielectric and piezoelectric properties of the ceramics have been investigated. The results indicate that a small amount of AF can improve the sintering performance and piezoelectric properties of the ceramics effectively. The KNN–AF ceramics for x = 0.03 show the best piezoelectric properties: d ₃₃ = 116 pC/N, k _p  = 32.9 %, Q _m  = 114.8, T _C  = 382 °C, P _r  = 21.8 μC/cm². This also indicates that (1 ? x)KNN–xAF ceramics are a promising lead-free piezoelectric candidate material because of its good properties, low-temperature sintering characteristics and plenty of Al₂O₃ and Fe₂O₃ resources with low cost.     

Effect of sintering temperatures on properties of BaO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glass/silica composites for CBGA package

BaO–B₂O₃–SiO₂–Al₂O₃ (BBSA) glass/silica composites synthesized by solid-state reaction method were developed for CBGA packages, and the effects of sintering temperature (900–950 °C) on the phase transformation, microstructure, thermal, mechanical and electrical properties were investigated. XRD results show that the major phases quartz and cristobalite, and the minor phase BaSi₂O₅ are detected in BBSA composites. Furthermore, it was found that the quartz phase transforms to cristobalite phase at 930–940 °C. The formation of cristobalite phase with higher coefficient of thermal expansion (CTE) led to the increase of CTE value of BBSA composites. However, excessive cristobalite phase content would degrade the mechanical properties and the linearity of thermal expansion of the ceramics. BBSA composites sintered at 920 °C exhibited excellent properties: low dielectric constant and loss (ε_r = 6.2, tanδ = 10^?4 at 1 MHz), high bending strength (179 MPa), high CTE (12.19 ppm/°C) as well as superior linearity of the thermal expansion.     

Effects of Bi excess on the structure and electrical properties of high-temperature BiFeO3–BaTiO3 piezoelectric ceramics

BiFeO₃–BTiO₃(BF–BT) ceramics as a promising candidate for lead-free high-temperature piezoelectric ceramics were studied with a special emphasis on the compositional dependence of piezoelectric properties. Excess Bi was added to compensate for the evaporation of Bi³⁺ ions during sintering and this addition was found to be effective in improving the piezoelectric properties of BF–BT ceramics. The microstructure, dielectric and piezoelectric properties of excess Bi doped BF–BT ceramics were investigated. Maximum piezoelectric constant d ₃₃ = 142 pC/N and k _p = 0.302 were obtained with 0.04 Bi doping. At the same time, an enhanced Curie temperature T _c, 452 °C, was obtained. The combination of improved piezoelectric properties and increased T _c makes these ceramics suitable for elevated temperature piezoelectric devices.     

High piezoelectric and dielectric properties of 0–3 PZT/cement composites by temperature treatment

Temperature treatment of 0–3 type PZT/cement composites before polarization yielded high dielectric and piezoelectric properties in materials with 50% PZT inclusions by volume and 50% cement matrix. Specimens were treated at seven temperatures from 23 °C to 150 °C and then applied by a 1.5 kV/mm poling field. The dielectric loss of the composites reduces at higher pretreatment temperatures, shorting the trigger time. Temperature treatment increased the piezoelectric strain factor d₃₃, the relative dielectric constant ε_r and the piezoelectric voltage factor g₃₃ of PZT/cement composites, but did not affect significantly the electromechanical coupling coefficient K_t. Piezoelectric factors reach stable values after 70 days of aging, and samples that were not temperature pretreated reached stable values earlier. Specimens pretreated at 150 °C exhibit d₃₃ = 106.3 pC/N and ε_r = 477 on the 70^th aging day, almost two times greater than the composites without temperature treatment. The resonance frequency of the composites on the 70th day decreases with increasing temperature, with the exception of 150 °C. Temperature pretreatment can also improve the phase angle of the composites. In addition, the effect of curing time for PZT/cement composites is an important factor to dominate the feasibility of polarization.     

Effect of the adding of rod-like attapulgite upon the properties of polyimides produced by random copolycondensation

A series of polyimides (PIs) and polyimide/attapulgite (AT) composite films was successfully prepared by random copolycondensation. The polyimides were synthesized based on 4,4′-diaminodiphenyl ether, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), and 4,4′-oxydiphthalic anhydride (ODPA). By adjusting the ratio of BPADA and ODPA, three different types of anhydride group-terminated PIs were obtained. AT was functionalized by chemical modification with γ-aminopropyltriethoxysilane and then chemical bonded with PI via reaction between amino group and anhydride group, resulting in stable PI/AT composites. The structure and properties of PIs and PI/AT composites were characterized by FTIR, XRD, TG, SEM, DSC, DMA, mechanical measure, and so on. Comparison was given between PIs and PI/AT composites. Results showed that all PIs had good thermal stability and mechanical properties with glass translation temperature (T _g) over 210 °C, 5 % weight loss temperature (T _d,5%) over 494 °C and tension strength of 84–89.9 MPa, breaking elongation around 7 %. More stable, flexible, and much stronger films were obtained after adding 5 wt% AT, which showed 535–548.5 °C, 85.8–118.9 MPa, and 10.3–24.7 % in T _d,5%, tension strength, and breaking elongation, respectively. Much interestingly, we found that AT had the greatest effect on PI-2, the yielding of which occurred during mechanical measure, and PI/AT-2 composite displayed excellent comprehensive properties.     

Structure,ferroelectric, piezoelectric and ferromagnetic properties of BiFeO3–Ba0.6(Bi0.5K0.5)0.4TiO3 lead-free multiferroic ceramics

(1?x)BiFeO₃–xBa_0.6(Bi_0.5K_0.5)_0.4TiO₃ + 1 mol% MnO₂ lead-free multiferroic ceramics were fabricated by a conventional ceramic technique and the effects of Ba_0.6(Bi_0.5K_0.5)_0.4TiO₃ doping and sintering temperature on the microstructure, ferroelectric, piezoelectric and ferromagnetic properties of the ceramics were studied. All the ceramics show good electric insulation with the resistivity values of 1.97 × 10⁹–1.20 × 10¹⁰ Ω cm. After the addition of Ba_0.6(Bi_0.5K_0.5)_0.4TiO₃, two dielectric anomalies are observed at high temperatures (T ₁ ~ 453–710 °C and T ₂ ~ 716–755 °C, respectively). The ceramic with x = 0.275 exhibits the optimum piezoelectricity (d ₃₃ = 48 pC/N and k _p = 13.6 %, respectively). The Ba_0.6(Bi_0.5K_0.5)_0.4TiO₃ doping and the increasing in sintering temperature improve significantly the ferromagnetic properties of the ceramics. The ceramic with x = 0.25 sintered at 1,040 °C gives the optimum remnant magnetization M _r of 0.13 emu/g.     

Lead-free (Li, Na, K)(Nb, Sb)O3 piezoelectric ceramics: effect of Bi(Ni0.5Ti0.5)O3 modification and sintering temperature on microstructure and electrical properties

Lead-free (1 ? x)(K_0.475Na_0.475Li_0.05)(Nb_0.95Sb_0.05)O₃–xBi(Ni_0.5Ti_0.5)O₃ [(1 ? x)KNNL–xBNiT] piezoelectric ceramics were prepared by conventional solid-state sintering. The effect of BNiT addition and sintering temperature on phase structure, microstructure, and dielectric and piezoelectric properties of (1 ? x)KNNL–xBNiT ceramics was investigated. The results reveal that the addition of small amounts of BNiT causes significant changes in microstructures, crystalline structures, and dielectric and piezoelectric properties. The T _c values and dielectric constant at T _c of (1 ? x)KNNL–xBNiT ceramics are increased obviously with 0.2 % BNiT addition and decreased with further increasing BNiT content. Enhanced piezoelectric properties are obtained for the sample with x = 0.4 % and synthesized at optimal temperature of 1100 °C, in which d ₃₃ and k _p are 253 pC/N and 0.52, respectively. These results show that (1 ? x)KNNL–xBNiT ceramics are promising lead-free piezoelectric materials.     

Effects of MnO2 and sintering temperature on microstructure, ferroelectric, and piezoelectric properties of Ba0.85Ca0.15Ti0.90Zr0.10O3 lead-free ceramics

Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ + xmol% MnO₂ lead-free ceramics have been prepared by a conventional sintering method and the effects of MnO₂ and sintering temperature on microstructure, ferroelectric, and piezoelectric properties of Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ lead-free ceramics have been studied. The addition of 0.25 mol% MnO₂ promotes grain growth, improves the ferroelectricity of the ceramics and strengthens ferroelectric tetragonal–ferroelectric orthorhombic phase transition near 40 °C. Because of the coexistence of tetragonal and orthorhombic phases and the combinatory effects of soft and hard doping of Mn ions, the ceramic with x = 0.25 exhibits the optimum piezoelectric properties (d ₃₃ = 306 pC/N and k _p = 42.2 %, respectively). Excess MnO₂ inhibits the grain growth and degrades the ferroelectric and piezoelectric properties of the ceramics. Sintering temperature has an important influence on the microstructure, tetragonal–orthorhombic phase transition near 40 °C, ferroelectric and piezoelectric properties of the ceramics. The increase in sintering temperature leads to large grains and more noticeable tetragonal–orthorhombic phase transition near 40 °C, enhances ferroelectricity and thus improves effectively the piezoelectricity of the ceramics. The Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ ceramic sintered at 1350 °C possesses the optimum piezoelectric constant d ₃₃ value of 373 pC/N.