Planar Electromechanical Coupling Coefficient Kp Research Articles

LiNbO3-induced phase structure evolution and improved piezoelectric properties in BiFeO3–BaTiO3 ceramics

Eco-friendly (0.73-x)Bi1.05FeO3-xLiNbO3-0.27BaTiO3 ternary ceramics were designed and prepared via a solid-state sintering route. Based on the X-ray diffraction results and Rietveld refinement, it was found that the structure of the ceramics transformed from rhombohedral to tetragonal symmetry with the addition of LiNbO3, and at x = 0.003, there existed a morphotropic phase boundary separating the two phases. Near the phase boundary, the largest values were achieved for the piezoelectric constant d33 and planar electromechanical coupling coefficient kp, being 180 pC/N and 0.27, respectively. Due to the addition of LiNbO3, the grain size tended to become smaller. Additionally, the ceramics were transitioned from normal to relaxor ferroelectrics with increasing x. Despite the fact that the LiNbO3 addition would result in a gradual decrease of Curie temperature, a relatively high Curie temperature (535 °C) was still maintained at x = 0.003, the phase boundary composition, which also showed good temperature stability of piezoelectric properties. These experimental results can provide a reference for the practical applications of high-temperature lead-free ceramics.

Yttrium and Niobium Elements Co-Doping and the Formation of Double Perovskite Structure Ba2YNbO6 in BCZT.

The (Ba0.85Ca0.15) (Ti0.90Zr0.10)O3 + x Y3+ + x Nb5+ (abbreviated as BCZT-x(Nb + Y), x = 0 mol%, 0.05 mol%, 0.1 mol%, 0.2 mol%, 0.3 mol%) lead-free piezoceramics samples were prepared by a traditional solid-state sintering method. And the effects of Yttrium and Niobium elements (Y3+ and Nb5+) co-doping on the defect, phase and structure, microstructure, and comprehensive electrical properties have been investigated. Research results show that the Y and Nb elements co-doping can dramatically enhance piezoelectric properties. It is worth noting that XPS defect chemistry analysis, XRD phase analysis and TEM results together show that a new phase of double perovskite structure Barium Yttrium Niobium Oxide (Ba2YNbO6) is formed in the ceramic, and the XRD Rietveld refinement and TEM results show the coexistence of the R-O-T phase. Both these two reasons together lead to significant performance improvements of piezoelectric constant (d33) and planar electro-mechanical coupling coefficient (kp). The functional relation between temperature and dielectric constant testing results present that the Curie temperature increases slightly, which shows the same law as the change of piezoelectric properties. The ceramic sample reaches an optimal performance at x = 0.1% of BCZT-x(Nb + Y), where d33 = 667 pC/N, kp = 0.58, εr = 5656, tanδ = 0.022, Pr = 12.8 μC/cm2, EC = 2.17 kV/cm, TC =92 °C, respectively. Therefore, they can be used as potential alternative materials to lead based piezoelectric ceramics.

Enhanced Piezoelectric, Ferroelectric, and Electrostrictive Properties of Lead-Free (1-x)BCZT-(x)BCST Electroceramics with Energy Harvesting Capability.

Next-generation electronics and energy technologies can now be developed as a result of the design, discovery, and development of novel, environmental friendly lead (Pb)-free ferroelectric materials with improved characteristics and performance. However, there have only been a few reports of such complex materials' design with multi-phase interfacial chemistry, which can facilitate enhanced properties and performance. In this context, herein, novel lead-free piezoelectric materials (1-x)Ba0.95 Ca0.05 Ti0.95 Zr0.05 O3 -(x)Ba0.95 Ca0.05 Ti0.95 Sn0.05 O3 , are reported, which are represented as (1-x)BCZT-(x)BCST, with demonstrated excellent properties and energy harvesting performance. The (1-x)BCZT-(x)BCST materials are synthesized by high-temperature solid-state ceramic reaction method by varying x in the full range (x = 0.00-1.00). In-depth exploration research is performed on the structural, dielectric, ferroelectric, and electro-mechanical properties of (1-x)BCZT-(x)BCST ceramics. The formation of perovskite structure for all ceramics without the presence of any impurity phases is confirmed by X-ray diffraction (XRD) analyses, which also reveals that the Ca2+ , Zr4+ , and Sn4+ are well dispersed within the BaTiO3 lattice. For all (1-x)BCZT-(x)BCST ceramics, thorough investigation of phase formation and phase-stability using XRD, Rietveld refinement, Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), and temperature-dependent dielectric measurements provide conclusive evidence for the coexistence of orthorhombic + tetragonal (Amm2 + P4mm) phases at room temperature. The steady transition of Amm2 crystal symmetry to P4mm crystal symmetry with increasing x content is also demonstrated by Rietveld refinement data and related analyses. The phase transition temperatures, rhombohedral-orthorhombic (TR-O ), orthorhombic- tetragonal (TO-T ), and tetragonal-cubic (TC ), gradually shift toward lower temperature with increasing x content. For (1-x)BCZT-(x)BCST ceramics, significantly improved dielectric and ferroelectric properties are observed, including relatively high dielectric constant εr ≈ 1900-3300 (near room temperature), εr ≈ 8800-12900 (near Curie temperature), dielectric loss, tan δ ≈ 0.01-0.02, remanent polarization Pr ≈ 9.4-14 µC cm-2 , coercive electric field Ec ≈ 2.5-3.6kV cm-1 . Further, high electric field-induced strain S ≈ 0.12-0.175%, piezoelectric charge coefficient d33 ≈ 296-360 pC N-1 , converse piezoelectric coefficient ≈ 240-340 pm V-1 , planar electromechanical coupling coefficient kp ≈ 0.34-0.45, and electrostrictive coefficient (Q33 )avg ≈ 0.026-0.038 m4 C-2 are attained. Output performance with respect to mechanical energy demonstrates that the (0.6)BCZT-(0.4)BCST composition (x = 0.4) displays better efficiency for generating electrical energy and, thus, the synthesized lead-free piezoelectric (1-x)BCZT-(x)BCST samples are suitable for energy harvesting applications. The results and analyses point to the outcome that the (1-x)BCZT-(x)BCST ceramics as a potentially strong contender within the family of Pb-free piezoelectric materials for future electronics and energy harvesting device technologies.

Enhanced piezoelectric activity around orthorhombic-tetragonal phase boundary in multielement codoping BaTiO3

Lead-free piezoelectric ceramics (Ba1-xCax)(Ti0.97Zr0.01Sn0.01Ce0.01)O3 (x = 0, 0.0125, 0.025, 0.0375, 0.05, 0.075, 0.1) have been prepared by conventional solid-reaction method. X-ray diffraction and variable temperature dielectric measurements confirm the coexistence of orthohombic and tetragonal phase near room temperature at x = 0.025. With the presence of the polycrystalline phase transitions (PPT) effect, the ceramic with x = 0.025 demonstrates an excellent electrical property with piezoelectric coefficient d33 of 523 pC/N, planar electromechanical coupling coefficient kp of 49% and strain of 0.093%.

Preparation, Structure, and Electrical Properties of Cobalt-Modified Bi(Sc3/4In1/4)O3-PbTiO3-Pb(Mg1/3Nb2/3)O3 High-Temperature Piezoelectric Ceramics.

Cobalt-modified 0.40Bi(Sc3/4In1/4)O3–0.58PbTiO3–0.02Pb(Mg1/3Nb2/3)O3 ceramics (abbreviated as BSI–PT–PMN–xCo) were produced by conventional two-step solid-state processing. The phase structure, micro structure morphology, and electrical properties of BSI–PT–PMN–xCo were systematically studied. The introduction of Co ions exerted a significant influence on the structure and electrical properties. The experiment results demonstrated that Co ions entered the B-sites of the lattice, resulting in slight lattice distortion and a smaller lattice constant. The average grain size increased from ~1.94 μm to ~2.68 μm with the increasing Co content. The optimized comprehensive electrical properties were obtained with proper Co-modified content 0.2 wt.%. The Curie temperature (Tc) was 412 °C, the piezoelectric constant (d33) was 370 pC/N, the remnant polarization (Pr) was 29.2 μC/cm2, the relatively dielectric constant (εr) was 1450, the planar electromechanical coupling coefficient (kp) was 46.5, and the dielectric loss (tanδ) was 0.051. Together with the enhanced DC resistivity of 109 Ω cm under 300 °C and good thermal stability, BSI–PT–PMN–0.2Co ceramic is a promising candidate material for high-temperature piezoelectric applications.

Fabrication and properties of 3-3 type PZT-ordinary Portland cement composites

In this study, porous lead zirconate titanate (PZT) ceramics with porosity ranging from 46.4% to 82.3% were produced by the gel casting technology of particle-stabilized ceramic foams with the solid loading of 5–25 vol%, then the Portland cement paste was cast in porous PZT ceramics with continuous vibration to fabricate 3-3 type cement-based piezoelectric composites. The microstructure, dielectric, piezoelectric, and electromechanical coupling properties of the composites were characterized. With the increase in initial solid loading of PZT slurry, both the porosity, open porosity and pore size of porous PZT ceramics decreased correspondingly, which have prevented the filling of cement paste into the porous ceramics and led to the increment of PZT content in the composites. Increase in the PZT content contributed to the relative permittivity (εr) and longitudinal piezoelectric strain coefficient (d33), and a resultant reduction in piezoelectric voltage coefficient (g33). The prepared composites possessed a maximal thickness electromechanical coupling coefficient (Kt) value of 41.22%, higher than that of planar electromechanical coupling coefficient (Kp), indicating enhanced thickness mode oscillations of the composite. With the increase in PZT volume fraction, the PZT-cement composites turned from typical 3-3 structure to appoximate sandwich structure gradually, leading to more energy loss during electromechanical process and obvious decrease of the mechanical quality factor (Qm). The acoustic impedance (Z) of specimens ranged from 6.69 to 8.27 MRayls, close to that of cement materials (∼10 MRayls), making them promising candidate for application in civil engineering.

Effects of MnO2 addition on the structure and electrical properties of PIN-PZN-PT ceramics with MPB composition

A two-step fabrication route was used to synthesize piezoelectric ceramics 0.35Pb(In1/2Nb1/2)O3-0.40Pb(Zn1/3Nb2/3)O3-0.25PbTiO3-xwt% MnO2 (PIN-PZN-PT-xMn, x = 0.0–2.0), and the corresponding structural changes and variations in electrical parameters caused by Mn modification were also investigated. The addition of MnO2 was quite effective to reduce the sintering temperature of PIN-PZN-PT ceramics. A pure perovskite structure was obtained in all sintered samples by XRD tests. The Curie temperature TC, piezoelectric constant d33, dielectric loss tanδ and planar electromechanical coupling coefficient kp gradually decreased as the MnO2 addition content increases, while the mechanical quality factor Qm increased. The diffusive phase transition behavior became strong with increasing the MnO2 doping content. A relatively high Qm value on the order of 420 has been obtained at the 2 wt% MnO2-added ceramic, which is six times higher than that of the undoped PIN-PZN-PT sample. These results indicate that Mn-doped PIN-PZN-PT ceramics show a broad prospect in the applications of electromechanical device requiring high power and high temperature.

Structural, Piezoelectric and Dielectric Properties of K0.4Na0.6NbO3-Bi0.5Li0.5ZrO3-CaZrO3 Ternary Lead-Free Piezoelectric Ceramics

The Bi0.5Li0.5ZrO3 and CaZrO3 co-modified (K,Na)NbO3-based ceramics, with a formula of (0.98-x)K0.4Na0.6NbO3-xBi0.5Li0.5ZrO3-0.02CaZrO3, were designed to form a rhombohedral-tetragonal phase boundary, and a conventional solid-state sintering method was employed to prepare them. X-ray diffraction analysis revealed that a pure perovskite structure could be maintained in the studied composition range 0 ≤ x ≤ 0.05. Dielectric-temperature measurements were performed to further identify the phase structure of the ceramics, which was found undergoing a gradual evolution from an orthorhombic to a rhombohedral structure with increasing x. Furthermore, a rhombohedral-tetragonal phase boundary was observed to be formed at x = 0.035, near which enhanced piezoelectric properties were obtained, with piezoelectric constant d33 = 241 pC/N and planar electromechanical coupling coefficient kp = 0.37. Additionally, an investigation was conducted of the influence of Bi0.5Li0.5ZrO3 addition on the microstructure and paraelectric-ferroelectric phase transition of the ceramics as well. We believe that the findings in this current work can deepen our understanding of the role of Bi0.5Li0.5ZrO3 in the construction of a phase boundary and improvement of piezoelectric properties for (K,Na)NbO3-based ceramics.

Composition-driven phase evolution and piezoelectric properties of (1−x)(K0.48Na0.52)0.96Li0.04Nb0.95Sb0.05O3−xBi0.5 (Na0.84K0.16)0.48Ba0.02ZrO3 lead-free ceramics

In this study, we investigated the correlation between the phase structure, electrical properties and composition of lead-free (1-x)(K0.48Na0.52)0.96Li0.04Nb0.95Sb0.05O3-xBi0.5(Na0.84K0.16)0.48Ba0.02ZrO3 ceramics, which were prepared by a normal oxide sintering method. X-ray diffraction analysis revealed that all the studied compositions had a pure perovskite structure. Meanwhile, the structural evolution with composition was researched by combining the x-ray diffraction results with the temperature-dependent dielectric data, and a rhombohedral-tetragonal phase boundary was identified to exist in x = 0.01 to 0.05. Additionally, the grain size of the ceramics was found to gradually decrease with the increase of x, due to the inhibition effect of added Bi3+, Ba2+ and Zr4+ ions on the growing of the grains during sintering process. The ceramics exhibited the optimal piezoelectric properties at compositions near the phase boundary, with the highest piezoelectric constant d33 and the largest planar electromechanical coupling coefficient kp of 262 pC/N and 0.42, respectively.

Microstructure related properties enhancing in Ce-doped CaBi2Nb2O9 high temperature piezoelectric ceramics

CexCa1−xBi2Nb2O9 (CCBN, x = 0 ∼ 0.08) bismuth layered structural piezoceramics with pure orthorhombic symmetry were fabricated by conventional processing method. The microstructure of CCBN ceramics was obviously correlated with Ce doping content. Small Ce doping content (x ≤ 0.04) suppressed the sheet morphology of the ceramics, in favor of forming small particle-like grains. However, the grains grown and turned into sheet structure again when Ce doping content x ≥ 0.06. The CCBN ceramics with Ce doping content x = 0.04, owing to its microstructure of small and uniform particle-like grains, exhibited enhancing properties as follows: piezoelectric constant d33 = 10.3 pC/N, planar electromechanical coupling coefficient kp = 11.5%, dielectric constant = 106, and dielectric loss tanδ = 0.28%. In addition to high resistivity (ρ = 8.7 × 107 Ω cm at 500 °C) and good thermal stability up to 800 °C, this ceramic sample should very promising for high temperature sensing applications.

Enhanced piezoelectric properties of Sr(1.7)(Na0.5Bi0.5)0.3Bi4Ti5O18 ceramics in the system Sr(2−x)(Na0.5Bi0.5)xBi4Ti5O18 (where 0 ≤ x ≤ 0.5)

AbstractFine powders synthesized via sol‐gel route were employed to fabricate Sr(2−x)(Na0.5Bi0.5)xBi4Ti5O18 (SNBT, where x = 0, 0.1, 0.25, 0.3, 0.4, and 0.5) ceramics. The composition (x)‐dependent structural changes associated with SNBT ceramics were analyzed using X‐ray powder diffraction, transmission electron microscopy, and Raman spectroscopic techniques. Average grain size analyses carried out on the SNBT ceramics by scanning electron microscopy revealed an important role played by the dopants in inhibiting the grain growth. Dielectric constants and the Curie temperature of the ceramics were found to decrease and increase, respectively, with increase in x. The increase in Curie temperature with increase in x was attributed to the decrease in the tolerance factor. The specific composition (x = 0.3) of the SNBT ceramics exhibited improved piezo‐ and ferroelectric properties associated with a higher Curie temperature (569 K). The piezoelectric coefficient (d33) and the planar electromechanical coupling coefficient (kp) of SNBT(x = 0.3) were enhanced by 25% and 42%, respectively, as compared to the undoped ceramics.

Microstructures, phase evolution and electrical properties of (1-x)K0.40Na0.60Nb0.96Sb0.04O3-xBi0.5K0.5HfO3 lead-free ceramics

An investigation was carried out on the surface morphologies, crystal structures and electrical properties of lead-free piezoelectric (1-x)K0.40Na0.60Nb0.96Sb0.04O3-xBi0.5K0.5HfO3 ceramics, prepared by conventional solid-state reaction route. Based on X-ray diffraction results and temperature-dependent dielectric properties, we found that the ceramics experienced a structural evolution from orthorhombic phase to multi-phase coexistence and then to rhombohedral phase, with the increase of Bi0.5K0.5HfO3 content. Furthermore, a rhombohedral–tetragonal phase boundary was identified at x = 0.035, which was considered to be caused by the merging of rhombohedral-orthorhombic and orthorhombic-tetragonal phase transition temperatures. The ceramics exhibited an enhanced piezoelectric activity near the rhombohedral–tetragonal phase boundary, with a piezoelectric constant d33 of 230 pC/N and a planar electromechanical coupling coefficient kp of 0.340. In addition, a clear composition dependence was observed for the microstructure of the ceramics, which could be explained by the combined effect of vacancies and phase segregations.

Excellent piezoelectric properties and high Tc in Fe2O3-doped PMW-PNN-PZT ceramics

In this work, in order to develop piezoelectric ceramics sintered at low temperature with high piezoelectric d31 coefficient, Pb(Mg1/2W1/2)0.03(Ni1/3Nb2/3)0.09(Zr0.5Ti0.5)0.88O3 ceramics were fabricated as a function of the amount of Fe2O3 addition using a conventional mixed oxide method. The microstructure, dielectric and piezoelectric properties were systematically investigated as a function of amount of Fe2O3 addition. At the sintering temperature of 920 °C, the excellent values of density = 7.94 (g/cm3), piezoelectric coefficient (d31) = 246 pC/N, planar electromechanical coupling coefficient (kp) = 0.69, mechanical quality factor (Qm) = 213, dielectric constant (εr) = 2,682 and high Curie temperature =366 °C were obtained from the ceramics doped with 0.3 wt% Fe2O3, respectively.

Effect of excess Bi on the structure and electrical properties of CaBi2Nb2O9 ultrahigh temperature piezoceramics

CaBi2Nb2O9 + x wt% Bi2O3 (x = 0, 1, 2, 3) ceramics with bismuth layer structure were prepared by solid state reaction route. The effect of excess bismuth on the crystal structure, microstructure and electrical properties of the ceramics was investigated. At all compositions, orthorhombic symmetric bismuth layer structure was formed without secondary phases. Excess bismuth caused more uniform grains. The ceramic with excess Bi2O3 of 1 wt% exhibited optimal electrical properties as follows: piezoelectric constant d33 = 6.4 pC/N, planar electromechanical coupling coefficient kp = 11.0%, dielectric constant $$\varepsilon _{{33}}^{T}/{\varepsilon _0}$$ = 93.5, dielectric loss tanδ = 0.24%, and resistivity ρ = 2.9 × 106 Ω cm (@ 500 °C). This ceramic also possess ultrahigh Curie temperature Tc = 940 °C, indicating its potential application for high temperature sensors and actuators.

Mechanism of significantly enhanced piezoelectric performance and stability in textured potassium-sodium niobate piezoelectric ceramics

In this study, the piezoelectric coefficient d33 and planar electromechanical coupling coefficient kp were enhanced 145% and 71%, respectively for the <001>-textured (K0.5Na0.5)0.95Li0.05Nb0.93Sb0.07O3 piezoelectric ceramics compared with their randomly oriented counterpart. Significantly enhanced piezoelectric response in textured ceramics is originated from a combined effect of the intrinsic high piezoelectric activity of <001>-oriented grains in the tetragonal-orthorhombic phases, and easy polarization rotation of fine domains. Furthermore, a comparative analysis suggests that <001>-textured ceramics exhibit good thermal stability, benefiting from the weakened depolarization behavior via crystal orientation. The superior fatigue resistance in textured ceramics can be attributed to the reduced clamping effect as low defect density. These results show that high-performance textured ceramics reported in this work will be promising candidates in the field of lead-free piezoelectric materials.

Effects of Ge4+ acceptor dopant on sintering and electrical properties of (K0.5Na0.5)NbO3 lead-free piezoceramics

Lead-free (K0.5Na0.5)(Nb1-xGex)O3 (KNN-xGe, where x = 0-0.01) piezoelectric ceramics were prepared by conventional ceramic processing. The effects of Ge4+ cation doping on the phase compositions, microstructure and electrical properties of KNN ceramics were studied. SEM images show that Ge4+ cation doping improved the sintering and promoted the grain growth of the KNN ceramics. Dielectric and ferroelectric measurements proved that Ge4+ cations substituted Nb5+ ions as acceptors, and the Curie temperature (TC) shows an almost linear decrease with increasing the Ge4+ content. Combining this result with microstructure observations and electrical measurements, it is concluded that the optimal sintering temperature for KNN-xGe ceramics was 1020°C. Ge4+ doping less than 0.4 mol.%can improve the compositional homogeneity and piezoelectric properties of KNN ceramics. The KNN-xGe ceramics with x = 0.2% exhibited the best piezoelectric properties: piezoelectric constant d33 = 120 pC/N, planar electromechanical coupling coefficient kp = 34.7%, mechanical quality factor Qm = 130, and tanδ = 3.6%.

High piezoelectric d31 coefficient and high Tc in PMW-PNN-PZT ceramics sintered at low temperature

In this study, in order to develop piezoelectric ceramics with high piezoelectric d31 coefficient and high Curie temperature (Tc), Pb(Mg1/2W1/2)0.03(Ni1/3Nb2/3)0.09(Zr0.5Ti0.5)0.88O3 ceramics doped with sintering aids were fabricated using a columbite precursor method. The crystal structure, dielectric and piezoelectric properties were investigated as a function of calcination temperature. At the sintering temperature of 920°C, the optimal values of density=7.83(g/cm3), piezoelectric coefficient(d31)=263pC/N, piezoelectric coefficient(d33)=620pC/N, planar electromechanical coupling coefficient (kp)=0.689, mechanical quality factor (Qm)=100, dielectric constant(εr)=2524 and Curie temperature (Tc)=340°C were obtained from the ceramics with the two step calcination temperature of 1st=1130°C, 2nd=780°C, respectively, for haptic actuator application.

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

AbstractLow‐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 kp of 49%, peak permittivity εmax of 25 612, remanent polarization Pr 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.

Piezoelectric and dielectric behavior of 0-3 asphalt-based composites with carbon black

Asphalt-based piezoelectric composites have great potential to serve as sensors to monitor the health of asphalt pavements due to their compatibility with asphalt pavements and appropriate response behaviors. This paper reports the preparation of asphalt-based piezoelectric composites doped with carbon black to investigate the influence of lead zirconate titanate (PZT) and carbon black contents on the dielectric, piezoelectric, and electromechanical properties of the composites. The addition of carbon black as a conductive phase facilitates the poling process, which improves the poling efficiency. The results indicate that with increasing PZT content, the dielectric constant (εr), piezoelectric strain factor (d33) and planar electromechanical coupling coefficient (Kp) of the composites increase. εr, d33, and Kp of the composites increase with the increase of carbon black content, and the composites with 0.3vol% carbon black present the maximum values of 154.89, 75.74 pC/N and 37.73%, respectively, then decrease with greater carbon black content. However, tanδ shows an opposite trend with the variation of PZT and carbon black contents. With 80vol% PZT and 0.3vol% carbon black, tanδ decreases to the minimum value of 20.80, then increases with further increases in carbon black content. The variation of the mechanical quality factor (Qm) shows little association with the contents of PZT or carbon black.

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 %.