Enhancing piezoelectric properties of Ba0.88Ca0.12Zr0.12Ti0.88O3 lead-free ceramics by doping Co ions

The piezoelectric properties of lead-free Ba_0.88Ca_0.12Zr_0.12Ti_0.88O₃ (BCZT) ceramics were greatly optimized by doping Co ions using a CoO powder. The role of Co²⁺ and Co³⁺ in enhancing the piezoelectric properties and the relationship between the content ratio Co³⁺/Co²⁺ and piezoelectric performance were studied. The X-ray diffraction patterns of all samples indicated that crystalline phases were a BCZT-based single perovskite structure regardless of the Co ion content. The phase transition temperature and lattice distortion degree were related to the Co ion content and the content ratio Co³⁺/Co²⁺ because Co²⁺ resulted in higher oxygen vacancy generation, whereas Co³⁺ induced larger lattice shrinkage. The ceramic containing 0.10 wt% of Co ion showed the best piezoelectric and dielectric performance with the highest piezoelectric constant d₃₃ ~ 490 p.m./V at room temperature and the highest Curie temperature T_c of 110 °C, which increased by 29% and 16%, respectively. In this case, the content ratio Co³⁺/Co²⁺ reached the maximum value of 0.86. The high piezoelectric properties and phase stability of BCZT ceramics by doping Co ions make these ceramics promising piezoelectric materials for practical applications.     

掺杂离子及掺杂工艺对钛酸钡性能的影响

钛酸钡基陶瓷是一种新兴的多功能电子陶瓷材料，由于其优异的电学性能而在很多领域有着广泛的应用，掺杂离子以及掺杂工艺对钛酸钡的性能有显著的影响。对常用的几种掺杂离子，如钙、镁、铅、锶、锆、锡和稀土元素，以及各种掺杂工艺对钛酸钡性能的影响进行了简单评述，并预测了未来的研究方向。     

Exploration on the origin of enhanced piezoelectric properties in transition-metal ion doped KNN based lead-free ceramics

In this work, we studied effects of Ni₂O₃ and Co₂O₃ doping on crystal structures, microstructures, orthorhombic and tetragonal phase transition temperature (T_o-t), and electrical properties of [Li_0.06(Na_0.57K_0.43)_0.94][Ta_0.05(Sb_0.06Nb_0.94)_0.95]O₃ (LNKTSN) lead-free ceramics. The experimental results showed that the Ni₂O₃ addition with appropriate amount could shift the T_o-t downwards to the room temperature, and thus obviously increasing the room-temperature piezoelectric coefficient (d₃₃), dielectric coefficient (ε_r) and electromechanical coupling coefficient (k_p) of the LNKTSN ceramics. These were consistent with previous experimental results obtained in Fe₂O₃ doped LNKTSN ceramics. On the contrary, Co³⁺ doping shifted continuously the T_o-t upward and deteriorated obviously piezoelectric properties of LNKTSN ceramics. Fe, Co and Ni had similar ion radii and were expected to result in the same (donor or acceptor) doping effects on electrical properties of LNKTSN ceramics. The different doping effects between Co³⁺ (deterioration) and Ni³⁺ or Fe³⁺ (improvement) on the electrical properties of LNKTSN ceramics suggested that the coexistence of orthorhombic and tetragonal phases at room temperature due to downward shift of T_o-t, rather than ion doping (donor or acceptor doping) effects was the main cause for enhanced room-temperature piezoelectric properties. This conclusion can be extended to all KNN-based materials in general, thus offering principle guide for future development of new lead-free materials with good piezoelectric properties.     

The effect of Er3+ doping on the structure and thermoelectric properties of CdO ceramics

The effect of Er³⁺ doping on the structure and thermoelectric transport properties of CdO ceramics was investigated. The solubility limit of Er³⁺ in CdO was very small and that additions of more than about 0.5 at% Er³⁺ resulted in the presence of Er₂O₃. With the addition of Er³⁺, the average grain size of Cd_1?xEr_xO (0 ≤ x ≤ 0.015) decreased and the carrier concentration as well as mobility increased at room temperature. A small amount of Er³⁺ doping resulted in a marked increase of electric conductivity and a moderate decrease of Seebeck coefficient. Although Er³⁺ doping also leaded to an increase in thermal conductivity, a large ZT of 0.2 was achieved in x = 0.005 sample at 723 K due to the obvious improvement of power factor. The results demonstrate that CdO:Er is a new promising n-type thermoelectric material.     

The Cr‐doping effect on white light emitting properties of Ce:YAG phosphor ceramics

The Cr/Ce‐doped YAG transparent ceramic was fabricated by the solid‐state reaction in vacuum. The Cr/Ce‐doped YAG ceramic phosphor effectively complement the red spectral component and improve the color rendering performance when excited by blue light that is due to the effective energy transfer between Cr³⁺ ion and Ce³⁺ ion. However, the energy transfer from Ce³⁺ to Cr³⁺ ion leads to energy loss and therefore the luminous efficacy of the WLED which is composed of blue LED chip and the Cr/Ce‐doped YAG ceramic phosphor decreases. The composite phase structure of ceramic phosphor is designed for improving the extraction efficacy and increasing the luminous efficacy by breaking the total internal reflection (TIR) at the interface between air and ceramic.     

Enhanced piezoelectric properties of Sm3+-modified PMN-PT ceramics and their application in energy harvesting

Piezoelectric materials are widely used in electromechanical energy conversion, such as in sensors, transducers, and self-powered materials. In this paper, the influence of the Sm doping content on the microstructure and ferroelectric, piezoelectric, dielectric, and field-induced strain properties of 0.70Pb(Mg_1/3Nb_2/3)O₃-0.30PbTiO₃ (PMN-PT) ceramics was investigated. Sm-doped PMN-PT ceramics with both high piezoelectric properties (d₃₃～1406 pC/N) and a large electromechanical coupling coefficient (k_p～0.69) were synthesized. Based on their piezoelectric effect, a maximum output voltage of 31 V was achieved under external forces. The output voltages showed satisfactory stability, repeatability, and sensitivity under periodic external forces; hence, Sm-doped PMN-PT piezoelectric ceramics are potential candidates for energy conversion and signal monitoring.     

Effect of Fe substitution on the piezoelectric,dielectric and ferroelectric properties of PNZST ceramics

Fe-doped (Pb_0.99Nb_0.02)[(Zr_0.70Sn_0.30)_0.52Ti_0.48]_0.98O₃ (PNZST) ceramics were prepared via conventional solid state reaction method, and the effect of Fe doping on their structural and electrical properties was investigated in detail. Results showed that Fe³⁺ cations could dissolve into readily the B-sites of perovskite structure for the PNZST ceramics with the less amount of Fe content (≤0.8 wt%), resulting in the full densification after sintered at 1300 °C. Meanwhile, Fe doping caused a structure transform from the tetragonal to the rhombohedral. The better electric properties for PNZST ceramic with 0.6 wt% Fe content were obtained, i.e. piezoelectric constant d₃₃=380 pC/N, electromechanical coupling factor k_p=0.57, mechanical quality factor Q_m=225, dielectric constant ε_r=1190, loss tangent tan δ=0.007 and curie temperature T_c=318 °C.     

Effect of BiNbO4 doping on the dielectric properties of BaTiO3 ceramics

In this paper, the effect of BiNbO₄ doping on the structural characteristics and dielectric properties were investigated systematically. With the increase in the BiNbO₄ content, a systematic structural characteristics change from ferroelectric tetragonal to cubic phase. Dielectric properties changed from classical ferroelectric behavior to dispersive relaxor‐like behavior, further to linear behavior. Because of the created defect dipoles, the long‐range dipolar interaction was interrupted and the weak couplings were formed. Energy storage density reached the maximum of 0.797 J/cm³ with energy efficiency of 92.5% in 0.9BT‐0.1BN. The nonlinearity was suppressed obviously, which could enhance the energy storage density in lead‐free relaxor materials.     

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 structure and piezoelectric properties of CaBi2Nb2O9 ceramics by W6+-Doping

Calcium bismuth niobate (CaBi₂Nb₂O₉) is a typical bismuth-layer structured piezoelectrics (BLSPs) with a high Curie temperature (T_C) of ～943 °C, but it has low piezoelectric coefficient and high-temperature resistivity which severely limits signal acquisition in the high-temperature piezoelectric vibration sensors. Ion-doping modification is regarded as an effective way to enhance electrical properties. In this work, W⁶⁺ donor-doping at Nb⁵⁺ site in the CaBi₂Nb_2-xW_xO₉ (x = 0, 0.020, 0.025, 0.030, 0.035 and 0.040) piezoelectric ceramics with T_C of 931 ± 2 °C were fabricated by the conventional solid-state reaction method. The effects of W⁶⁺-doping on crystal structure of CaBi₂Nb_2-xW_xO₉ as well as microscopic morphology and electrical properties of ceramics were investigated systematically. The tetragonality, isotropy and electrical properties of the ceramics were enhanced with the introduction of W⁶⁺ dopant. It was found that x = 0.025 was the optimal W⁶⁺-doping ratio that yielded remnant polarization of 8.0 μC/cm², electrical resistivity of 3.0 × 10⁶ Ω cm at 600 °C, piezoelectric coefficient (d₃₃) of 14.4 pC/N, and good thermal depoling property. Our work has established a feasible approach to tune the structure of CaBi₂Nb₂O₉ to improve piezoelectric properties for potential applications in high-temperature piezoelectric vibration sensors.     

Impact of sandblasting on the mechanical properties and aging resistance of alumina and zirconia based ceramics

Bioinert zirconia and alumina ceramic devices are widely used, both in orthopaedics and in dentistry. In order to improve their bonding with bone tissues or dental resin cements, their surfaces are often roughened at different scales. In this work, we have investigated the effects of the same sandblasting treatment on alumina, zirconia and a zirconia-toughened alumina, focusing on their mechanical performance and the interplay between surface defects and residual stresses. Additionally, we explored the impact of the treatment on the hydrothermal aging of the two zirconia-containing materials. Residual stresses generated during sandblasting were always predominant over surface defects but their effect varied with the material: while they had a weakening effect on alumina, they reinforced both zirconia-containing materials. Finally, we found that the monoclinic grains at the surface of sandblasted zirconia recrystallized into tetragonal nanograins after annealing and this led to an increased resistance to aging.     

Effect of Ag+ doping and Ag addition on the thermoelectric properties of KSr2Nb5O15

The electron and phonon thermal transport behavior of Ag ⁺ doped KSr₂Nb₅O₁₅ were discussed by using the first-principles calculations. The band gap was reduced after Ag⁺ doping, and the electrons near the Fermi level had stronger transition capability, which effectively increased the carrier concentration and electrical conductivity and reduced the thermal conductivity, thereby improving the ZT of the doped KSr₂Nb₅O₁₅ from 0.6298 to 0.7214 (1200 K) under ideal conditions. In addition, the solid-state reaction method was used to prepare Ag nanoparticle added KSr₂Nb₅O₁₅ samples, and their thermoelectric performance was tested. The experimental results and the calculated results showed a good consistent trend in which Ag improved the thermoelectric properties of KSr₂Nb₅O₁₅. When the amount of addition of nanosized Ag was 20 wt%, the power factor and ZT of the material were the highest at 1073 K, which were 0.228 mW/(K²·m) and 0.1090, respectively. This research shows how to improve the thermoelectric performance of KSr₂Nb₅O₁₅ ceramics and broaden their temperature range for application.     

The decrease of depolarization temperature and the improvement of pyroelectric properties by doping Ta in lead-free 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 ceramics

Ta-doped lead-free 0.94NBT-0.06BT-xTa (x=0.0–1.0%) ceramics were synthesized by a conventional solid-state route. XRD shows that the compositions are at a morphotropic phase boundary where rhombohedral and tetragonal phases coexist. The depolarization temperature (T_d) shifted to lower temperature with the increase of Ta content. The pyroelectric coefficient (p) of doped ceramics greatly enhanced compared with undoped material and reached a maximum of 7.14×10⁻⁴ C m⁻² °C⁻¹ at room temperature (RT) and 146.1×10⁻⁴ C m⁻² °C⁻¹ at T_d at x=0.2%. The figure of merits, F_i and F_v, also showed a great improvement from 1.12×10⁻¹⁰ m v⁻¹ and 0.021 m² C⁻¹ at x=0.0 to 2.55×10⁻¹⁰ m v⁻¹ and 0.033 m² C⁻¹ at x=0.2% at RT. Furthermore, F_i and F_v show the huge improvement to 52.2×10⁻¹⁰ m v⁻¹ and 0.48×10⁻¹⁰ m v⁻¹ respectively at T_d at x=0.2%. F_C shows a value between 2.26 and 2.42 ×10⁻⁹ C cm⁻² °C⁻¹ at RT at x=0.2%. The improved pyroelectric properties make NBT-0.06BT-0.002Ta ceramics a promising infrared detector material.     

Effects of Hf4+ substitute on the enhanced electrostrain properties of 0.7BiFeO3-0.3BaTiO3-based lead-free piezoelectric ceramics

The 0.7Bi_1.05FeO₃-0.3BaHf_xTi_(1?x)O₃ (BF-BHT-x) ceramics are prepared by using conventional method. The mechanism of large electric-induced strain is studied in detail through Rietveld refinement, transmission electron microscopy (TEM), and piezoelectric force microscopy (PFM). The BF-BHT-0.05 ceramics, which possess the coexistence of cubic (Pm-3m) and rhombohedral (R3c) phase proved by Rietveld refinement and TEM measurement, have the maximum electric-induced strain of S_max = 0.58% at 130 kV/cm (1 Hz). The reduced potential barrier is beneficial to the switching and reorientation of domain under an external electric field due to the coexistence of cubic and rhombohedral phase. A mass of nanodomains embedded into the microdomains, which is conducive to domain switching, are observed obviously through PFM. Therefore, the findings show that the large strain is because the external electric field drives the conversion mixed phase into the major rhombohedral phase, the reduced potential barrier, and the nanodomain in macrodomain.     

Processing and enhanced electrical properties of Sr1-x(K0.5Bi0.5)xBi2Nb2O9 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics, Sr_1−x(K_0.5Bi_0.5)_xBi₂Nb₂O₉ (SKBN-x, x=0, 0.2, 0.5, 1.0), were synthesized by a conventional solid-state reaction. Structural and electrical properties of SKBN-x ceramics were investigated. X-ray diffraction analysis suggested that the substitution led to the formation of a layered perovskite structure. Plate-like morphologies for the grains were clearly observed in all the samples, which are characteristic for layer-structure Aurivillius compounds. The Curie temperature (T_c) is found to shift to higher temperature from 445 °C to 509 °C with increasing (K, Bi) content. Excellent remanent polarization (2P_r∼15 μC/cm²) were obtained for SKBN-0.2 ceramic. High piezoelectric coefficient of d₃₃∼21  pC/N were obtained for the samples at x=0.5. Additionally, thermal annealing studies indicated that the piezoelectric coefficient (d₃₃) of SKBN-0.5 was unchanged even if annealing temperature increased to be 450 °C, demonstrating the ceramics are the promising candidates for high-temperature applications.     

Vanadium doping effects on microstructure and dielectric properties of barium titanate ceramics

V-doped barium titante ceramics were prepared by conventional solid state reaction method. XRD patterns show that V⁵⁺ ions have entered into the tetragonal perovskite structure of solid solution to substitute for Ti⁴⁺ ions on the B sites. Addition of vanadium accelerates grain growth of BTO ceramics and there is abnormal grain growth of barium titanate ceramics with higher vanadium concentration. Vanadium doping can increase the Curie temperature and decrease the dielectric loss of barium titanate ceramics. As vanadium concentration increases, the remnant polarization of V-doped BTO ceramics begins to increase and reaches the maximum and then decreases. The coercive electric field for V-doped barium titanate ceramics decreases with the increasing of vanadium concentration. As temperature rises, the remnant polarization and the coercive electric field of V-doped barium titanate ceramics decrease simultaneously.     

Grain size effect on piezoelectric and ferroelectric properties of BaTiO3 ceramics

A series of dense barium titanate (BaTiO₃, BTO) ceramics with different grain sizes (GS) were prepared by two-step sintering method. The effect of GS on piezoelectric coefficient (d₃₃) and planar electromechanical coupling factor (k_p) displayed a trend similar to that on relative permittivity (ɛ′). The values of d₃₃, k_p, and ɛ′ increased significantly with decreasing GS, reaching maximum values (ɛ′ = 6079, d₃₃ = 519 pC/N and k_p = 39.5%) at approximately 1 μm, and then decreased rapidly with further decreasing GS. The results revealed that high-performance BTO ceramics could be effectively prepared by controlling GS. Polarization–electric field hysteresis loops and temperature dependence of ɛ′ were also investigated.