Planar Electromechanical Coupling Coefficient Kp Research Articles

Grain size-dependent dielectric, piezoelectric and ferroelectric properties of Sr2Bi4Ti5O18 ceramics

Fine powders comprising nano-crystallites of Sr2Bi4Ti5O18 (SBT) were synthesized via citrate-assisted sol–gel route. Different ceramics of SBT with different grain sizes (93 nm–1.42 μm) were fabricated by varying sintering temperatures and durations. The usage of nano-crystalline powders for fabricating ceramics facilitated lower sintering temperatures. The grain growth in these powder compacts was found to be controlled by the grain boundary curvature mechanism, associated with the activation energy of 181.9 kJ/mol. Interestingly, with a decrease in grain size there was an increase in structural distortion which resulted in a shift of Curie temperature (phase transition) toward higher temperatures than that of conventional bulk ceramics. Extended Landau phenomenological theory for the spherical ferroelectric particles was invoked to explain experimentally observed size-dependent phase transition temperature, and the critical size for SBT is predicted to be 11.3 nm. Grain size-dependent dielectric, ferroelectric and piezoelectric properties of the SBT ceramics were studied and the samples comprising average grain size of 645 nm exhibited superior physical properties that include remnant polarization (2Pr) = 16.4 μC cm−2, coercive field (Ec) = 38 kV cm−1, piezoelectric coefficient (d33) = 22 pC N−1 and planar electromechanical coupling coefficient (kp) = 14.8 %.

Compositional inhomogeneity and segregation in (K0.5Na0.5)NbO3 ceramics

In this report, the effects of the calcination temperature of (K0.5Na0.5)NbO3 (KNN) powder on the sintering and piezoelectric properties of KNN ceramics have been investigated. KNN powders are synthesized via the solid-state approach. Scanning electron microscopy and X-ray diffraction characterizations indicate that the incomplete reaction at 700°C and 750°C calcination results in the compositional inhomogeneity of the K-rich and Na-rich phases while the orthorhombic single phase is obtained after calcination at 900°C. During the sintering, the presence of the liquid K-rich phase due to the lower melting point has a significant impact on the densification, the abnormal grain growth and the deteriorated piezoelectric properties. From the standpoint of piezoelectric properties, the optimal calcination temperature obtained for KNN ceramics calcined at this temperature is determined to be 800°C, with piezoelectric constant d33=128.3pC/N, planar electromechanical coupling coefficient kp=32.2%, mechanical quality factor Qm=88, and dielectric loss tanδ=2.1%.

Effects of GeO2 Addition on Sintering and Properties of (K0.5Na0.5)NbO3 Ceramics

Lead‐free (K0.5Na0.5)NbO3 (KNN) piezoelectric ceramics doped with different amounts of GeO2 were prepared and characterized. GeO2 was found to effectively improve the sinterability and piezoelectric properties of the material. The improvement in the sinterability is ascribed to the formation of a liquid phase, which decreased the sintering temperature from 1080°C to 1010°C. The improvement in the properties is attributed to the replacement of Nb5+ with Ge4+ to form acceptor dopants. The following optimized properties were obtained from the KNN ceramic with 0.75 wt% GeO2: piezoelectric constant (d33) = 126 pC/N, planar electromechanical coupling coefficient (kp) = 42.8%, mechanical quality factor (Qm) = 140, and dielectric loss (tanδ) = 3.8%.

Microstructure and Electrical Properties of Eu-Doped K0.5Na0.5NbO3 Ceramics

(K0.5Na0.5)1–3xEuxNbO3 (0≤x≤0.05) lead-free ceramics have been prepared by a conventional solid state reaction. XRD show that the ceramics possess a pure perovskite structure with orthorhombic symmetry. Dopant Eu restrains the grain growth, decreases the ferroelectric-paraelectric phase transition temperature and leads to a diffuse phase transition. With the increase of Eu, the observed remanent polarization (Pr) decreases while the coercive field (Ec) remains almost unchanged. Nevertheless, for the increase in relative permittivity, the sample with x = 0.005 exhibits the optimum piezoelectric properties, giving a large piezoelectric coefficient (d33 = 121 pC/N) and a high planar electromechanical coupling coefficient (kp = 0.41).

Templated grain growth and piezoelectric properties of 〈001〉-textured PIN–PMN–PT ceramics

Abstract

Influence of Co Ion Doped Amount on Property of BCTZ Piezoelectric Ceramics Sintered at Low Temperature

Ba0.85Ca0.15Ti0.9Zr0.1O3 (abbreviated as BCTZ) lead-free piezoelectric ceramics co-doped with Li2CO3(0.6 wt.%) and different Co ion content (x = 0, 0.25, 0.4, 0.6, 0.8 wt.%) were prepared by conventional solid state reaction method. Influence of Co ion doped amount on the phase structure, microstructure, piezoelectric properties and dielectric properties of prepared BCTZ piezoelectric ceramics doped with Li2CO3 were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD) and other analytical methods. The results show that Co2+ and Co3+ instead of Zr4+ did not change the crystal structure and all the BCTZ piezoelectric ceramics possessed single phase perovskite structure with orthorhombic symmetry when Co ion doped amount was less than 0.6 wt.%. When Co ion doped amount was 0.8 wt.%, impurity phase appeared in the ceramics. The piezoelectric constant(d33), planar electromechanical coupling coefficient (kp), the dielectric constant (ϵr) and the relative density of BCTZ ceramics increased first and then decreased, the dielectric loss (tanδ) of BCTZ ceramics decreased first and then increased at the same time, the optimize sintered temperature (ts) decreased while Co ion doped amount increased. The influence of Co ion doped amount on the properties of BCTZ ceramics doped with Li2CO3 were caused by lattice distortion and “hard effect” piezoelectric additive. The BCTZ ceramics had the optimum properties, which d33 was 316 pC/N, tanδ was 0.021, kp was 0.43, ϵr was 3209, the sintered temperature was 1010°C, the relative density was 99%, while Co ion doped amount was 0.60 wt.% and Li2CO3 doped amount was 0.6 wt.%.

Effect of borax addition on sintering and electrical properties of (K0.5Na0.5)NbO3 lead-free piezoceramics

Lead-free piezoelectric ceramics (K0.5Na0.5)NbO3 (KNN) doped with borax (Na2B4O7·10H2O) as sintering aid were prepared using conventional ceramic processing. All the ceramics possessed the perovskite structure with orthorhombic symmetry. Results revealed that borax is an effective additive for improving the sinterability and piezoelectric properties of KNN. The KNN with 0.45wt% borax showed optimal properties as follows: piezoelectric constant d33=131.6 pC/N, planar electromechanical coupling coefficient kp=34.8%, mechanical quality factor Qm=109, and dielectric loss tanδ=3.80%.

Temperature-Dependent Properties of a 1–3 Connectivity Piezoelectric Ceramic–Polymer Composite

Abstract In this work, the 1–3 connectivity piezoelectric ceramic–polymer composites have been fabricated by a viscous-polymer processing, where 0.90Pb(Zr0.52Ti0.48)O3–0.05Pb(Mn1/3Sb2/3)O3–0.05Pb(Zn1/3Nb2/3)O3 (PZT–PMS–PZN) fibers with 0.5 volume fraction were aligned in epoxy matrix. The sintered PZT fibers, with average diameter of 300 μm and aspect ratio (height/diameter) higher than 3, all showed a pure perovskite phase structure and highly dense morphology. The dielectric, piezoelectric, ferroelectric properties and the vibration modes of the 1–3 composites were measured and demonstrated in comparison with that of the monolithic piezoelectric ceramics. The results confirmed that the 1–3 composites possessed a low acoustic impedance (Z) of 13 MRayl and a high thickness coupling coefficient (k t) of 0.59, in addition, only single thickness vibration mode with the resonance frequency over 1.5 MHz was observed. With temperature elevation, the properties including dielectric constant εr , k t, the ratio of k t to k p (k t/k p) and the acoustic impedance (Z) increase, while the planar electromechanical coupling coefficient (k p) show opposite temperature dependence. Under test temperature of 100°C, the 1–3 composites still present excellent temperature stability with increased k t/k p ratio up to 3.6. The researches on temperature-dependent properties of the 1–3 composites are critical for improving its applications in various environments.

Phase structure and electrical properties of xPZN–(1−x)PZT piezoceramics near the tetragonal/rhombohedral phase boundary

xPb(Zn1/3Nb2/3)O3–(1−x)PbZr0.5Ti0.5O3 (xPZN–(1−x)PZT) (x=0.22–0.36) polycrystalline ceramics with finely varied PZN content were fabricated by a solid-state reaction method. The phase structure, microstructure and temperature dependence of the electrical properties were systematically investigated. The core of the morphotropic phase boundary (MPB) separating the tetragonal from rhombohedral phases located around the region with x=0.26–0.30, identified by XRD measurement and electrical properties. Higher PZN content favored rhombohedral symmetry and stronger relaxor-like characteristics. All compositions demonstrated well-saturated ferroelectric P–E loops, and a maximum remnant polarization of Pr~41.83μC/cm2 with a corresponding coercive field Ec~11.3kV/cm was achieved around MPB. Optimum electrical properties of piezoelectric constant d33~550pC/N, planar electromechanical coupling coefficient kp~0.69, relative dielectric permittivity εr~2327 were obtained in the 0.28PZN–0.72PZT composition with a relatively high Curie point of Tc~325°C. This composition also possessed a good electric field-induced-strain property with d33⁎ up to 658pm/V (E=1kV/mm), making it promising for application in piezoactuators.

Electric field induced cubic to monoclinic phase transition in multiferroic 0.65Bi(Ni1/2Ti1/2)O3-0.35PbTiO3 solid solution

The results of x-ray diffraction studies on 0.65Bi(Ni1/2Ti1/2)O3-0.35PbTiO3 solid solution poled at various electric fields are presented. After poling, significant value of planar electromechanical coupling coefficient (kP) is observed for this composition having cubic structure in unpoled state. The cubic structure of 0.65Bi(Ni1/2Ti1/2)O3-0.35PbTiO3 transforms to monoclinic structure with space group Pm for the poling field ≥5 kV/cm. Large c-axis microscopic lattice strain (1.6%) is achieved at 30 kV/cm poling field. The variation of the c-axis strain and unit cell volume with poling field shows a drastic jump similar to that observed for strain versus electric field curve in (1 − x)Pb(Mg1/3Nb2/3) O3-xPbTiO3 and (1 − x)Pb(Zn1/3Nb2/3)O3-xPbTiO3.

Influence of cement matrix on properties of 1–3–2 connectivity cement-based piezoelectric composite

In order to develop cement-based piezoelectric intelligent composites suitable for concrete structural health monitoring, 1–3–2 type piezoelectric composites were fabricated by using piezoelectric ceramic as the functional component and epoxy resin and different kinds of cement as the matrix. The properties of the composites were studied. The results show that, compared with pure piezoelectric ceramic, the relative dielectric factor ε33of the composite decreased while the dielectric loss tan δ33increased. The planar electromechanical coupling coefficient Kp, mechanical quality factor Qmand acoustic impedance Z of all the composites decreased, while the thickness electromechanical coupling coefficient Ktincreased. The composite with ordinary Portland cement matrix had the largest values of ε33, tan δ33, Ktand d33(piezoelectric strain factor).

Investigation of (1−x)(Bi0.94La0.06)(Ga0.05Fe0.95)O3–xPbTiO3 ceramics for high temperature applications

BiFeO3–PbTiO3 binary system doped with small amount of La3+ and Ga3+ was investigated for the development of piezoelectric ceramics with high Curie temperatures. Crystalline solutions of (1−x)(Bi0.94La0.06)(Ga0.05Fe0.95)O3–xPbTiO3 (BLGF–xPT) for x=0.35, 0.37, 0.4 and 0.45 have been fabricated by the solid-state reaction method. X-ray diffraction reveals that BLGF–PT has a single perovskite structure with a mixed phase region at x=0.35–0.37. The dielectric constant (K), loss tangent (tanδ), Curie temperature (TC), remnant polarization (Pr) and piezoelectric constant (d33) of 700, 0.021, 532°C, 30μC/cm2 and 63pC/N respectively, have been achieved for x=0.35. The strain under the electric field of 90kV/cm was measured to be 0.107% for x=0.37 and the planar electro-mechanical coupling coefficient (Kp) of 19% was stable under 310°C, about 60% of its TC, indicating high thermal stability of the piezoelectric properties.

Effect of Na excess on the dielectric and piezoelectric properties of (Na0.53 K0.47 )(Nb0.55 Ta0.45 )O3 ceramics

Na-excess (Na0.53+xK0.47)(Nb0.55Ta0.45)O3 ceramics (x = 0.0, 0.005, 0.01, 0.015, 0.02, and 0.03) were prepared through the solid-state reaction method. The effects of Na excess and Ta substitution on dielectric behaviors and piezoelectric properties were investigated. Crystallized single phases were confirmed using X-ray diffraction. In particular, the orthorhombic–tetragonal polymorphic phase-transition temperature (TO–T) was observed near room temperature, and the piezoelectric properties were enhanced, even for small Na excesses and Ta substitution. The optimized piezoelectric coefficient d33 and planar electromechanical coupling coefficient kp were estimated to be 320–340 pC/N and 0.36, respectively.

Dielectric and Piezoelectric Properties of Ta-modified (K0.53Na0.47)(Nb0.8Ta0.2)O3 Ferroelectric Ceramics

Ta-substituted Na0.53K0.475Nb0.8Ta0.2O3 ceramics were prepared through the solid-state reaction method. The crystallized single phases were confirmed by X-ray diffraction. The temperature dependences of the dielectric and piezoelectric properties were investigated. Ta substitution in Na0.5K0.5NbO3 enhanced the piezoelectric property, and the corresponding piezoelectric coefficient was estimated to be d33 = 160 pC/N. With increasing temperature, the planar electromechanical coupling coefficient (kp ) increased linearly up to the orthorhombic-tetragonal phase-transition temperature (TO-T ) and decreased as the temperature comes closer to the Curie temperature (Tc ).

Preparation, characterisation, and electrical properties of (K0.5Na0.5)NbO3 lead-free piezoelectric ceramics

Na0.5 K0.5NbO3 (KNN) ceramics were sintered at different temperatures (970 °C, 1000 °C, 1030 °C, 1060 °C, and 1090 °C) for 3 h by a pressureless sintering method. The powders had been synthesised by sol–gel method, using citric acid as a coordination agent and ethylene glycol as an esterifying agent. The effects of temperature on the phase, microstructure, dielectric, ferroelectric, and piezoelectric properties of the as-prepared ceramics were analysed. The results revealed that all of the ceramics had a pure perovskite phase with orthorhombic symmetry. The piezoelectric constant (d 33), the relative dielectric constant (e r), the planar electromechanical coupling coefficient (K p), and the remnant polarization (P r) initially increased and then decreased with increasing of temperature in such KNN ceramics. The volatilization of sodium and potassium increased with increasing sintering temperature. Over the range of temperatures studied, those ceramics sintered at 1060 °C had the following optimal properties: (ρ = 3.97 g/cm3, d 33 = 119 pC/N, e r = 362.46, tan δ = 0.05, K p = 0.23, P r = 11.97 μC/cm2, E c = 10.35 kV/cm, and T c = 408 °C).

Low temperature sintering of high performance KNN-based lead-free piezoelectric ceramic using BCBM frit as sintering aid

High performance lead-free (K0.49Na0.51)0.98Li0.02(Nb0.77Ta0.18Sb0.05)O3 + 0.5 mol%BaZrO3 piezoelectric ceramic was selected as base material, while BaO-CuO-B2O3-MnO2 frit was used as sintering aid to lower the sintering temperature. The effect of BaO-CuO-B2O3-MnO2 frit doping amount on the sintering behavior, structure and electrical properties of the ceramics was investigated. The optimal sintering temperature of the ceramics decreased with the increase of frit doping amount. The ceramic with frit doping amount of 1.0 wt.%, sintered at a reduced temperature of 1100°C, exhibited optimal electrical properties as follows: piezoelectric constant d 33 = 345 pC/N, planar electromechanical coupling coefficient k p = 44.5 %, mechanical quality factor Q m = 135, dielectric constant e 33 = 1210, and dielectric loss tanδ = 0.018. Together with its relatively high T c = 195°C, this ceramic was an excellent candidate for replacing the lead-based piezoceramics in practical applications.

Effects of Mn-doping on the properties of (Ba0.92Ca0.08)(Ti0.95Zr0.05)O3 lead-free ceramics

Lead-free piezoelectric ceramics (Ba0.92Ca0.08)(Ti0.95Zr0.05)O3–xmol%Mn (BCTZ–xMn) were synthesized by a traditional solid-state reaction. Effects of Mn addition on the microstructure and electrical properties of ceramics were investigated in the composition range of 0⩽x⩽2.2. High mechanical quality factor of Qm=921 and low dielectric loss of tanδ=0.3% have been obtained at x=2.0. With the increase of Mn content, the piezoelectric constant d33 and planar electromechanical coupling coefficient kp decrease with deviation from the polymorphic phase transition (PPT) region, and the Curie temperature TC gradually decreases. The relative high d33, kp and TC still maintain about 224 pC/N, 33.6% and 102°C at x=2.0, respectively. These results indicate that the BCTZ–xMn ceramics are promising candidate for the lead-free piezoelectric applications.

Structure and piezoelectric properties of (1–x)K0.5Na0.5NbO3–xLiBiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1–x)(K0.5Na0.5)NbO3–xLiBiO3 [(1–x)KNN–xLB] (x=0, 0.0005, 0.002, 0.004, 0.006, 0.008, 0.010) were prepared by an traditional solid-state reaction. The microstructure and electrical properties of the ceramics were investigated. The results show that all (1–x)KNN–xLB ceramics possess pure perovskite structure when x=0.01, no trace of any secondary phase is detected, and the phase structure of the ceramics transits abnormally from orthorhombic to cubic. With the increase of the LB content, the size of grain gradually becomes small, the piezoelectric constant d33 and the planar electromechanical coupling coefficient kp first increases and then decreases. The d33 and kp of the ceramics reach their maximum values 115 pC/N at x=0.002 and 0.2701 at x=0.001, respectively. The dielectric constant er of the ceramics firstly increases evidently and then decreases with the increase of x, the maximum value 871.8 is obtained at x=0.006.

Effect of BBS‐Based Frit on the Low Temperature Sintering and Electrical Properties of KNN Lead‐Free Piezoceramics

Using BaO–B2O3–SiO2 (BBS)‐based frit as sintering aid, the K0.49Na0.51NbO3 (KNN) + x wt% BBS (x = 1.0, 1.5, 2.0 and 2.5) lead‐free piezoelectric ceramics were successfully fabricated by solid‐state reaction method under low‐sintering temperature of 1000°C. The effect of BBS frit doping amount on the structure and electrical properties of the ceramics was investigated. The KNN ceramics with 1.5 wt% BBS frit showed optimal properties as follows: piezoelectric constant d33 = 108 pC/N, planar electromechanical coupling coefficient kp = 41%, mechanical quality factor Qm = 225, relative dielectric constant εr = 410, dielectric loss tanδ = 0.57% and Curie temperature Tc = 400°C. This ceramic sample should be a good lead‐free candidate for actuators or high temperature sensors application due to its ultra‐low tanδ, relatively high Qm and Tc.

Effects of NaSbO3 on phase structure and electrical properties of K0.5Na0.5NbO3–LiTaO3–NaSbO3 piezoelectric ceramics

The (0.96–x)K0.5Na0.5NbO3–0.04LiTaO3–xNaSbO3 (abbreviated as KNN–LT–xNS, x = 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08) lead-free piezoelectric ceramics were fabricated by conventional ceramic technique. The crystal structure, dielectric, ferroelectric and piezoelectric properties of the ceramics were investigated. The Curie temperature (TC) and the polymorphic phase transition temperature (TO−T) of the ceramics decreased gradually with the increase of NaSbO3. In addition, a coexistence of orthorhombic and tetragonal phases in the ceramics was identified in the composition range of 0.05 ≤ x ≤ 0.08. The ceramic with a composition of x = 0.06, which was close to the orthorhombic side of the polymorphic phase transition (PPT) region, exhibited excellent electrical properties with piezoelectric coefficient d33 = 233 pC/N, planar electromechanical coupling coefficient kp = 0.328, remnant polarization Pr = 14.7 μC/cm2, coercive field Ec = 11.7 kV/cm, relative permittivity \( \varepsilon_{33}^{\text{T}} /\varepsilon_{0} \) = 1,033, and loss tangent tan δ = 0.063. The ceramics had relatively low Qm value in the range of 10–37.