Search

This work presents the effects of sintering temperature ranging from 1200 °C to 1300 °C at intervals of 20 °C on the crystal structure, ferroelectric properties, and electrocaloric effect (ECE) of Pb 0.8 Ba 0.2 ZrO 3. Samples sintered at 1240 °C, 1260 °C, and 1280 °C have large remanent polarization and small coercive field. Meanwhile, samples sintered at 1260 °C, 1280 °C, and 1300 °C possess large breakdown field strength. Samples sintered at 1260 °C for 4 h exhibit the optimal ferroelectric properties. Antiferroelectricity-ferroelectricity (AFE-FE) phase transition occurs at room temperature T 1 (279 K). Directly examining ECE at this temperature is meaningful, and the temperature change is 0.068 K at approximately 60 °C and 30 kV/cm. Results laid the foundation for studying the performance of ferroelectric and ECE within this phase-transition temperature range and provide a reference for new solid-state refrigeration technology. [ABSTRACT FROM AUTHOR]

Sodium cobalt oxides (Na x CoO 2 , denoted as NCO) have attracted considerable attentions as the promising candidate of high-temperature thermoelectric materials because of their high thermoelectric power, high thermal stability and non-toxicity. The performances of NCO materials are dependent on their crystal structure. In this paper, the crystal structure and thermoelectric properties for NCO samples prepared by the solid state method under different sintering temperatures are discussed. Importantly, a phase transformation is discovered in NCO ceramics by TG-DTA analysis. The structural transformation is probably caused by Na volatilization at high temperature. With increasing sintering temperature, the Na ion concentration decreases, and the valence state of the Co ions increases, which can influence the carriers transport properties. In addition, a large number of grain boundaries generated by the fine grain prepared under low sintering temperature can effectively decrease the thermal conductivity. Thus, the figure-of-merit ZT value can be enhanced by the large Seebeck coefficient and low thermal conductivity in the low-temperature phase. [ABSTRACT FROM AUTHOR]

Abstract: Li/Ta/Sb co-doped lead-free (K0.4425Na0.52Li0.0375)(Nb0.93−x Ta x Sb0.07)O3 (abbreviated KNLNST x ) piezoelectric ceramics, with Ta-doping ratio of x ranging from 0.0275 to 0.0675, were synthesized using the conventional solid-state reaction method at the sintering temperature of 1130°C. The effects of Ta content on the microstructure, dielectric properties, and phase transition behavior of the prepared ceramics were systematically investigated. The X-ray diffraction results show that all KNLNST x ceramics formed a secondary phase, which is assigned to the tetragonal tungsten-bronze type (TTB) structure phase, and showed a phase transition from an orthorhombic symmetry to a tetragonal symmetry across a composition region of 0.0375

Abstract: A facile hydrothermal route via high temperature mixing method was used to synthesize (K, Na) (Nb, Ta)O3 lead-free piezoelectric ceramic powders. The influence of Ta doping and K+/(K+ +Na+) molar ratios in the starting solution on the resultant powders were investigated by X-ray diffraction, scanning electron microscope, transmission electron microscopy, and selected area electron diffraction. The Ta element was successfully doped into the alkaline niobate structure to form crystalline (K, Na) (Nb, Ta)O3 lead-free piezoelectric ceramics powder. The microstructure, piezoelectric, ferroelectric, and dielectric properties of the sintered (K, Na) (Nb, Ta)O3 ceramics from the obtained powders were investigated. The piezoelectric coefficient (d 33), electromechanical coupling coefficient (k p), dielectric constant (ɛ r), and remnant polarization (P r) of the sample sintered at 1180°C show optimal values of 210pC/N, 34.0%, 2302, and 19.01μC/cm2, respectively. [Copyright &y& Elsevier]

Abstract: BaTiO3 (BT) powders were synthesized by the hydrothermal method for fabricating lead-free barium titanate piezoelectric ceramics. The obtained powders were washed by distilled water and 0.01N acetic acid solutions separately, and utilized to obtain piezoelectric ceramics by traditional sintering. BT ceramics with the highest piezoelectric properties (d 33 value is over 190 pC/N) was obtained from the BT powder synthesized at 250°C and washed by acetic acid solution. The influence of washing method and sintering temperature on the piezoelectric properties of BT ceramics were studied. The reasons were investigated by comparing the properties of BT powders and their compacts sintered at different temperature. [Copyright &y& Elsevier]

The unique antiferroelectric behavior of AgNbO 3 ceramics has great potential for energy storage applications, which have attracted increasing attention. However, the relatively low recoverable energy storage density, energy efficiency and breakdown strength of AgNbO 3 ceramics severely limit their application in practice. In the present work, (Bi 0.2 Sr 0.7)TiO 3 was introduced to improve the relaxation behavior in AgNbO 3 ceramics via two-step sintering, which contributed to a high breakdown strength of 580 kV/cm. A recoverable energy storage density of 7.8 J/cm3 and an energy efficiency of 56 % were obtained in 0.90AgNbO 3 -0.10(Bi 0.2 Sr 0.7)TiO 3 ceramics. Moreover, the benign energy storage performance could be maintained at elevated temperatures, variable frequencies and cyclings up to 105. These results demonstrate the great potential of AgNbO 3 -based ceramics for energy storage applications. [ABSTRACT FROM AUTHOR]

Designed component of 0.95Al 2 O 3 –0.015Yb 2 O 3 –0.01MgO–0.025SiO 2 (95Al 2 O 3 –Yb/Mg/Si) ceramics were prepared by the traditional mixed-oxide method in the sintering temperature range of 1450–1700 °C. The influence of sintering temperature on the crystal structure, densification, microstructure, mechanical, friction and wear properties of 95Al 2 O 3 -YbMgSi ceramics were systematically investigated. XRD and SEM analysis results revealed that the increase in sintering temperature was very beneficial to eliminate the pores, increase the density and grain size, which obeys the common grain growth law. Both the flexural strength and hardness of obtained samples were increased almost linearly when the sintering temperature increased from 1450 °C to 1700 °C. The ceramics sintered at 1650 °C showed the optimum properties: H v = 1812.3, σ = 151.3 MPa, μ = 0.41, ρ = 3.72 g/cm3 and K c = 8.06e−5 mm3/N·m, respectively. Furthermore, the results of friction and wear experiments suggested that the 95Al 2 O 3 –Yb/Mg/Si ceramic prepared at the optimizing sintering process exhibited more stable friction state and lower wear degree under non-lubricated conditions. The enhanced mechanical properties could be attributed to their structure densification, pore elimination and gain growth with the increase of sintering temperature. [ABSTRACT FROM AUTHOR]

Sodium niobate nanopowders (N-NaNbO 3 ) and submicron powders (M-NaNbO 3 ) were synthesized by the solvothermal and hydrothermal route, respectively. Subsequently, their sintering activities were comparably investigated through a modified solid-state sintering process. It's found that N-NaNbO 3 green bodies presented an apparent shrinkage after the calcination at 650 °C, and dense N-NaNbO 3 ceramics can be obtained at 950 °C. Besides, the optimized sintering temperature of N-NaNbO 3 ceramics was 100 °C lower, yet the shrinkage was four times larger when compared with M-NaNbO 3 samples. Importantly, N-NaNbO 3 samples showed improved dielectric properties in the whole frequency range, and the room temperature relative dielectric constant (ε r ) of N-NaNbO 3 samples sintered at 950 °C was as high as ~8000. The improved permittivity of N-NaNbO 3 samples was attributed to the compact microstructure, unique crystalline structure and less oxygen vacancies. At the same time, the effect of abnormal phase transition behavior originated from the metastable structure was considered to explain the enhanced room temperature permittivity. It's believed that the solvothermal route has great potentials in the synthesis of alkali niobate ceramics powders with high activity for low-temperature sintering. [ABSTRACT FROM AUTHOR]

Lead zirconate titanate Pb(Zr x Ti 1− x )O 3 films with various Zr/Ti ratios of 20/80, 40/60, 52/48, 60/40 and 80/20 are deposited on highly dense CoFe 2 O 4 ceramics using a simple chemical solution deposition. All Pb(Zr x Ti 1− x )O 3 films are polycrystalline and have no preferential orientations. The dielectric, ferroelectric, piezoelectric and magnetoelectric properties strongly depend on the Zr/Ti ratio. And the Pb(Zr x Ti 1− x )O 3 films with a Zr/Ti ratio close to morphotropic phase boundary exhibit best properties, whose magnetoelectric coefficient is over 1.5 times larger than those of other Zr/Ti ratios. The introduction of a PbO seeding layer between the Pb(Zr 0.52 Ti 0.48 )O 3 films and CoFe 2 O 4 substrates facilitates the (100)-texture. Therefore, the magnetoelectric coefficient was enhanced by 1.5 times. The further improvement of the magnetoelectric coupling could be anticipated by fabricating Pb(Zr 0.52 Ti 0.48 )O 3 films with more or absolute (100)-texture and using conductive interfacial layer between two phases. [ABSTRACT FROM AUTHOR]

To analyze the effect of PFN content on the microstructure and electrical properties of x Pb(Fe 0.5 Nb 0.5)O 3 –(0.57− x)Pb(Ni 1/3 Nb 2/3)O 3 –0.43Pb(Zr 0.3 Ti 0.7)O 3 , the doping of x PFN–PNN–PZT) were systematically studied with 0.015 ≤ x ≤ 0.075. XRD patterns and Raman spectra analysis reveal that PFN diffuses into PNN–PZT perovskite lattice and forms new quaternary solid solution. With the increase of PFN content x , the proportion of rhombohedral (R) phase decreases gradually, whereas the proportion of tetragonal (T) phase displays a contrary trend. In particular, R – T coexistence near MPB was observed at x = 0.045. Meanwhile, optimized electrical properties of d 33 = 961 pC/N, k p = 0.716, ε r = 6298, and tan δ = 3.1% are achieved for the 0.045PFN–PNN–PZT ceramics. Moreover, the ceramics at MPB showed larger remnant polarization P r = 24.55 μC/cm2, smaller coercive field E c = 0.36 kV/mm, and lower dielectric relaxor degree γ = 1.813. All these results reveal that the enhanced electrical properties could be attributed to synergistic phase boundary motion, dielectric relaxor behavior and ferroelectric hysteresis effect. [ABSTRACT FROM AUTHOR]

Monodisperse Dy-doped BaTiO 3 nanopowders ( x DBT) with x =0, 1, 2, 3, 4, 5 mol% has been synthesized via a modified sol-hydrothermal method. And the influence of Dy 3+ on the crystal structure, micromorphology and dielectric properties of x DBT ceramics has been investigated. It’s found that Dy 3+ slightly affects the shape of the x DBT nanopowders, whereas excess Dy 3+ would cause the formation of the Dy(OH) 3 impurity. In addition, the grain growth during a sintering process is suppressed with the Dy 3+ incorporation. Further, the possible occupation of the Dy 3+ has been extrapolated based on the variation of lattice volume and phase composition. A self-compensation mode involving the simultaneously occupation at Ba-site and Ti-site is observed in the samples with 4 mol% Dy. Importantly, stabilized temperature-dependent dielectric properties has been achieved at x =4 mol%, resulting from the diffuse phase transition behaviors (the calculated diffuse factor γ =1.952) induced by chemical inhomogeneity. [ABSTRACT FROM AUTHOR]

Quaternary piezoelectric ceramics Pb(Ni1/3Nb2/3)O3–Pb(Fe1/2Nb1/2)O3–Pb(Zr0.3Ti0.7)O3–xZnO (PNN–PFN–PZT–xZ, x=0.0–0.08 in molar ratio) were prepared by the conventional mixed-oxide method. The effects of ZnO content on the microstructure and piezoelectric properties were systematically investigated. Increasing ZnO additive promotes the phase structure transformation from rhombohedral to tetragonal, indicating the presence of the morphotropic phase boundary in the ZnO-modified PNN–PFN–PZT system. The results show that ZnO doping significantly improves the coercive field (E c ), Curie temperature (T c ), and temperature stability (Δf r /f r 30°C, Δd 31/d 31 30 °C) of the PNN–PFN–PZT–xZ ceramics, although the piezoelectric constant (d 33, d 31) decreases slightly with increasing ZnO content. Taking into consideration the piezoelectric property and temperature stability, the obtained ceramic sample with x=0.04 exhibited favorable properties, which are listed as follows: d 33=810pC/N, k p =0.647, ε r =6243, tan δ=2.74%, E c =4.7kV/cm, and T c =136°C. [ABSTRACT FROM AUTHOR]

Abstract: (K, Na)NbO3-based lead free materials have been found to exhibit good piezoelectric properties due to the orthorhombic–tetragonal polymorphic phase transition (PPT) temperature compositionally shifted downward to near room temperature. However, this transition correspondingly results in a strong temperature dependence of the dielectric and piezoelectric properties. In this work, new quaternary (1−x) (K0.4425Na0.52Li0.0375)(Nb0.8925Sb0.07Ta0.0375)O3 (KNLNST)–xSrTiO3 (ST) lead-free piezoelectric ceramics were fabricated by a conventional ceramic technique and their structure and piezoelectric properties were also studied. The results of X-ray diffraction reveal that SrTiO3 diffuses into the KNLNST lattices to form a new solid solution with a perovskite structure. After the addition of SrTiO3, tetragonal–orthorhombic phase transition shifts to lower temperatures. The good piezoelectric properties of 0.995 KNLNST–0.005 ST material were found to be d 33∼295pC/N, k p∼42%, and ε r∼1902, with greatly improved temperature stability over the temperature range of 0–100°C, demonstrating practical potential for actuator and ultrasonic transducer applications. [Copyright &y& Elsevier]

Abstract: Two-step sintering was applied to manufacture a typical Li- and Ta/Sb-modified alkaline niobate-based lead-free piezoelectric ceramics. The sintering condition dependences of dielectric constants and piezoelectric properties were investigated. Under the optimal condition, dense specimens have an average grain size of approximately 5μm, and show good dielectric and piezoelectric properties. Significantly, the (K0.4425Na0.52Li0.0375) (Nb0.8925Sb0.07Ta0.0375)O3 ceramics sintered under the condition “1130/10/1020/15” show the peak values of the piezoelectric coefficient (d 33), electromechanical coupling coefficient (k p), and dielectric constant (ɛ), which are 281pC/N, 50% and 1500, respectively, owing to the densest microstructure of typical bimodal grain size distributions. Furthermore, the KNLNST ceramics maintain relatively low dielectric loss over wide temperature ranges. The result indicates that the KNLNST ceramics sintered by two-step sintering exhibit good temperature stability. [Copyright &y& Elsevier]

Abstract: Lead-free (K0.4425Na0.52Li0.0375) (Nb0.9625−x Sb x Ta0.0375)O3 piezoelectric ceramics were prepared by the conventional sintering method. The effects of the Sb content on the phase structure, microstructure, dielectric, piezoelectric, and ferroelectric properties of the (K0.4425Na0.52Li0.0375) (Nb0.9625−x Sb x Ta0.0375)O3 ceramics were investigated. The much higher Pauling electronegativity of Sb compared with Nb makes the ceramics more covalent. By increasing x from 0.05 to 0.09, all samples exhibit a single perovskite structure with an orthorhombic phase over the whole compositional range, and the bands in the Raman scattering spectra shifted to lower frequency numbers. The grain growth of the ceramics was improved by substituting Sb5+ for Nb5+. Significantly, the (K0.4425Na0.52Li0.0375) (Nb0.8925Sb0.07Ta0.0375)O3 ceramics show the peak values of the piezoelectric coefficient (d 33), electromechanical coupling coefficient (k p ), and dielectric constant (ɛ), which are 304pC/N, 48% and 1909, respectively, owing to the densest microstructure of typical bimodal grain size distributions. Besides, the underlying mechanism for variations of the electrical properties due to Sb5+ substitution was explained in this work. [Copyright &y& Elsevier]

AgNbO 3 -based ceramics have been the spotlight for the lead-free dielectric capacitors due to its unique antiferroelectric feature and the ever-increasing environmental concerns. Herein, synergic modulation on the energy storage properties of AgNbO 3 -based ceramics was reported, in which the over-stoichiometrical introduction of only 0.10 wt% MnO 2 at the atomic-scale leads to reduced leakage current, P r and enhanced antiferroelectric stability while the SiO 2 coating on the AgNbO 3 particles at the micro-scale greatly inhibits the grain growth, increases the breakdown strength and the electric filed inducing the AFE-FE transitions. As a result, a large recoverable energy density up to 3.34 J/cm3 with efficiency of 60.0% was obtained in 0.10 wt% MnO 2 -doped AgNbO 3 @SiO 2 ceramic, which is 2.3 times larger than that of the pristine AgNbO 3. This work provides a rational approach to synergically modulate the energy storage properties. [ABSTRACT FROM AUTHOR]

The combination of magnetic and dielectric materials is an effective and efficient approach to enhance microwave absorption performance. In this work, rGO/Zr4+-Ni2+ gradient-doped BaM composites were fabricated for broad microwave absorption bandwidth. The results show that the permittivity increases while the permeability reduces gradually with the rising of rGO content. With the mass ratio of rGO increasing up to 15%, the relatively high attenuation constant and good impedance matching condition lead to an outstanding microwave absorption performance with a broad bandwidth of 8.16 GHz and a minimum reflection loss of −57.07 dB at a thin matching thickness of 2.0 mm. Compared with the pure gradient-doped BaM sample, the bandwidth has been widened by 37.37% and the minimum reflection loss has been improved by 220.43%. The performance is also superior to most of the existing state-of-art absorbers. [ABSTRACT FROM AUTHOR]

Understanding the phase structure evolution is important for developing high performance lead-free piezoelectric materials. In this work, the effects of A-site ionic size of monovalent ions on the phase transition behaviors for the lead-free niobate ceramics ANbO 3 (A = Li, Na, Ag, and K) are investigated using XRD analysis and dielectric measurement. The iso-valent ionic doping restrains the relaxation behavior that usually appears in the hetero-valent ionic-doped niobate ceramics. The A-site average ionic size of R A and its ionic radius differences of ΔR A are found to be crucial influence factors on the phase transition behaviors of the ANbO 3 ceramics. Small Li+ doping stabilize tetragonal phase of the ANbO 3 ceramics with R A > 1.47 Å, but stabilize rhombohedral phase of the ones with R A < 1.47 Å. On the other hand, The ANbO 3 ceramics without Li+ doping prefer to orthorhombic phase due to indistinctive ionic size differences (ΔR A < 0.25 Å). Our results suggest that a certain phase and phase transition boundary could be designed by appropriate ionic doping for developing the niobate-based lead free piezoelectric ceramics. [ABSTRACT FROM AUTHOR]