Improvement on ferroelectric and piezoelectric properties of (K0.5Na0.5)NbO3 ceramic with Sr0.53Ba0.47Nb2O6 addition

(1 ? x)(K_0.5Na_0.5)NbO₃–xSr_0.53Ba_0.47Nb₂O₆ [(1 ? x)KNN–xSBN] ceramics were synthesized by solid-state reaction technique. X-ray diffraction analysis of samples indicated that a single orthorhombic perovskite phase was formed as the x value is ≤0.02. Optimized piezoelectric properties with d ₃₃ = 126 pC/N, K _p = 0.39, Q _m  = 201 were obtained for 0.98KNN–0.02SBN ceramic. The dielectric properties studies illustrated that both peaks of orthorhombic to tetragonal (T _O–T ) and ferroelectric tetragonal to paraelectric cubic (T _C ) phase transition shifted to lower temperature. The maximum remanent polarization (P _r  = 22.5 μC/cm²) for 0.98KNN–0.02SBN was obtained by the polarization versus electric field (P–E) researches. AC conductivity of samples increased with increasing the temperature. The calculated activation energy of the dc conductivity was 0.9654 eV, which may be due to thermal activation.     

An approach to further improve piezoelectric and ferroelectric properties of (K0.5Na0.5)NbO3 ceramic

In this communication, an approach to further improve the electrical properties of (K_0.5Na_0.5)NbO₃ (KNN) ceramic (abbreviated as KNN₂) was reported. For the conventional ceramic technique (abbreviated as KNN₁), the raw materials of K₂CO₃, Na₂CO₃ and Nb₂O₅ were directly used without further processing, while those for KNN₂ were ball milled before mixing. The powders prepared by KNN₂ exhibited smaller and uniform. The ceramics have higher densities than that of KNN₁, which significantly improved the piezoelectric and ferroelectric properties of ceramics. The KNN₂ ceramics exhibited very good piezoelectric properties with d₃₃ = 123 pC/N, k_p = 33.8 %, Q_m = 219.8 and P _r  = 20.2 μC/cm³, indicating that KNN₂ is a strategy to obtain a dense KNN ceramic with more excellent electrical properties.     

Electrical and microstructural properties of CaTiO3-doped K1/2Na1/2NbO3-lead free ceramics

Microstructure, electrical properties and dielectric behaviour of K_1/2Na_1/2NbO₃ (KNN) and CaTiO₃-modified K_1/2Na_1/2NbO₃ (CTO-KNN) systems, were investigated. Discs doped with 0 to 0·55% mol of CaTiO₃ (CTO) were sintered at 1125°C for 2 h. Although minority phases were found in doped samples, CaTiO₃ was not detected. It was also observed that CTO changed the microstructure and grain size of KNN drastically. Also, the Curie temperature and permittivity values decreased. Addition of CTO between 0·15 and 0·45 mol% decreases the density and dielectric values. Samples prepared with higher content of CTO than 0·45 mol% showed better electrical properties.     

Microstructure and properties of ZrO2-, TiO2-doped Ca–Si–B based ceramics

The microstructure, sintering and dielectric properties of ZrO₂-, TiO₂-doped Ca–Si–B based ceramics prepared by solid-phase process were investigated, and the effects of ZrO₂, TiO₂ content on these performances were analyzed. The Ca–Si–B based ceramics without additive (ZrO₂ or TiO₂) showed a high sintering temperature (1,100?°C) and had the dielectric properties: dielectric constant (ε_r) of 8.38, dielectric loss (tanδ) of 1.51?×?10^?3 at 1?MHz, and volume density of 2.47?g/cm³. The addition of ZrO_2, TiO₂ was revealed to lower the sintering temperature of Ca–Si–B based ceramics to 1,000?°C and enhance the sintering and dielectric properties: ρ?=?2.61?g/cm³, ε_r?=?5.85, tanδ?=?1.59?×?10^?4 (1?MHz) with ZrO₂ addition, and ρ?=?2.65?g/cm³, ε_r?=?6.12, tanδ?=?6.4?×?10^?4 (1?MHz) with TiO₂ addition, which are superior to the pure Ca–Si–B. The results show that ZrO₂, TiO₂ as nucleating agents, are conducive to the precipitation of crystals, thus decrease the sintering temperature and improve the dielectric properties of Ca–Si–B based ceramics.     

Structural and piezoelectric properties of barium-modified lead-free (K0.455Li0.045Na0.5)(Nb0.9Ta0.1)O3 ceramics

Ferroelectric (K_0.455Li_0.045Na_0.5)(Nb_0.9Ta_0.1)O₃ + x mol% BaCO₃ ceramic compositions with Ba²⁺ as an A-site dopant in the range of x = 0–1.2 mol% were synthesized by conventional ceramic processing route. Effect of Ba²⁺ content on the microstructure, ferroelectric, dielectric, and piezoelectric properties of the ceramics was investigated. The results of X-ray diffraction reveal that Ba²⁺ diffuse into the (K_0.455Li_0.045Na_0.5)(Nb_0.9Ta_0.1)O₃ lattices to form a solid solution with a perovskite structure having typical orthorhombic symmetry. As Ba²⁺ content increases, cell volume and tetragonality increase in the crystal structure of the ceramics. Increasing doping level of Ba²⁺ inhibits grain growth in the ceramics and reduces both the Curie temperature (T _c) and tetragonal–orthorhombic phase transition temperature (T _o-t). The bulk density, remnant polarization P _r, room-temperature dielectric constant (ε′_RT), planar electromechanical coupling factor k _p , and piezoelectric charge coefficient d ₃₃ are found to increase as Ba²⁺ concentration increases from 0 to 0.8 mol% and then decrease as Ba²⁺ content increases further from 0.8 to 1.2 mol%. High piezoelectric properties of d ₃₃ = 187 pC/N and k _p  = 48 % are found in 0.8 mol% Ba²⁺ composition. Optimum amount of Ba²⁺ dopant takes the polymorphic phase boundary region consisting of orthorhombic and tetragonal crystal structures of the ceramic system near the room temperature and enhances its piezoelectric properties.     

Microstructure and electrical properties of MgO-doped SnO2 varistor ceramics

The effect of MgO addition on the properties of (Co, Nb, Cr)-doped SnO₂ varistors was investigated. The samples with different MgO concentrations were fabricated by the conventional ceramic method and sintered at 1,250, 1,300, 1,350 and 1,400 °C for 2 h. It was found that the nonlinear coefficient presented a peak value of 28 and lowest leakage current density of 7 μA/cm² when 0.5 mol% MgO was added. The breakdown electrical field increased from 174 to 531 V/mm with increasing MgO from 0.0 to 2.0 mol%. The relative dielectric constant decreased with increasing MgO from 0.0 to 0.5 mol%, but increased with more MgO added. The dielectric loss decreased obviously in the case of low frequency with MgO added, and it had the lowest value when 0.5 mol% MgO added. The optimal samples were obtained by doping MgO with 0.5 mol% and sintering at 1,350 °C.     

Energy storage performance of silica-coated k0.5Na0.5NbO3-based lead-free ceramics

Potassium sodium niobate-based ceramics have been extensively studied as high-power energy storage capacitor in recent years due to their excellent dielectric properties. We investigated the microstructure, dielectric-temperature spectrum, and energy storage properties of SiO₂-coated 0.9(k_0.5Na_0.5)NbO₃–0.1Bi(Zn_2/3Nb_1/3)O₃ (0.9KNN–0.1BZN) ceramics prepared by solid-state sintering and Stöber method. During the sintering process, SiO₂ reacted with 0.9KNN–0.1BZN to form the second phase K₃Nb₃O₆Si₂O₇. Coating SiO₂ could improve the dielectric-temperature stability of 0.9KNN–0.1BZN ceramics, and had excellent performance adapting to high-temperature conditions. When the SiO₂ content is 1.0 wt%, the maximum energy storage density of 0.9KNN–0.1BZN ceramics is 0.97 J/cm³, and the breakdown field strength is 200 kV/cm. This work expands the application of (k_0.5Na_0.5)NbO₃ ceramics in the field of energy storage capacitors.

     

Enhanced pyroelectric properties of lead free KNN/P(VDF-TrFE) composite film by optimizing KNN sintering temperature

The effect of potassium-sodium niobate (KNN) powder sintering temperature on the structure and properties of the KNN/{poly(vinylidenefluoride-co-trifluoroethylene 70:30) [P(VDF-TrFE) 70:30]} composite thick films have been studied in this paper. KNN powders were sintered by solid-state reaction at different temperatures ranging from 750 to 900 °C. Then the KNN powders were used to fabricate composite thick films by casting the KNN/P(VDF-TrFE) suspension on to ITO substrates. The pyroelectric and dielectric properties of the composite thick films have been investigated systematically. It was found that sample made up of KNN ceramic powders sintered at 850 °C show optimal properties for pyroelectric appliance. The highest pyroelectric coefficient was 63 μCm^?2/K and the highest detectivity figure-of-merit was 4.94 μPa^1/2.     

Low temperature sintering of Li1.1Nb0.58Ti0.5O3-xBi2O3 dielectric with adjustable temperature coefficient

Ceramics of Li_1.1Nb_0.58Ti_0.5O₃-xBi₂O₃ with low sintering temperature have been prepared by the solid-solution reaction method using B₂O₃ (2 wt% added) as sintering aid. For all compounds, the sintering temperature achieves 900 °C. Microstructure and dielectric properties of Li_1.1Nb_0.58Ti_0.5O₃-2 wt% B₂O₃-xBi₂O₃ (LNT-B-xBi) ceramics have been investigated. The X-ray diffraction patterns indicate for higher Bi₂O₃ content (x = 0.1 mol%) that the material is composed by two phases identified as M-phase and Bi₄Ti₃O₁₂. The Li_1.1Nb_0.58Ti_0.5O₃ + 0.15 mol% Bi₂O₃ composition sintered at 900 °C with B₂O₃ addition exhibits attractive dielectric properties (ε _r = 59.68, tan δ = 1.2×10^?4 and a temperature coefficient of the relative permittivity near zero) at 1 MHz. It is also shown that the introduction of Bi₂O₃ can tune the temperature coefficient of the relative permittivity. All dielectric properties lead this system compatible to manufacture sliver based electrodes multilayer dielectric devices.     

Dielectric behavior and energy storage properties in BaO–SrO–Nb2O5–B2O3 system glass–ceramics with Gd2O3 addition

A series of strontium barium niobate-based borate system glass–ceramics with Gd₂O₃ addition have been prepared by controlled crystallization method. The effect of Gd₂O₃ addition on the microstructure, phase evolution and dielectric properties has been investigated. The results show that the addition of Gd₂O₃ to the glass–ceramics changes the dielectric property and energy-storage density. Typically, the glass–ceramics with 0.5 mol% Gd₂O₃ heat treated at 630 °C/2 h + 800 °C/3 h possesses a dielectric constant of 136, a breakdown strength of 1,075 kV/mm and energy-storage density of 6.94 J/cm³, which is suitable for the application in high energy-storage capacitors.     

Effect of gadolinia addition on varistor characteristics of vanadium oxide–doped zinc oxide ceramics

The effect of gadolinia addition on microstructure, electrical and dielectric characteristics, and aging behavior of vanadium oxide–doped zinc oxide varistor ceramics was systematically investigated. The average grain size decreased from 5.6 to 5.2 μm with an increase in the amount of Gd₂O₃ up to 0.1 mol%, whereas a further increase caused it to increase to 5.7 μm at 0.25 mol%. The sintered densities decreased from 5.51 to 5.44 g/cm³ with an increase in the amount of Gd₂O₃. With increasing the amount of Gd₂O₃, the breakdown field increased from 4,800 to 5,365 V/cm up to 0.05 mol%, whereas a further increase decreased it to 4,781 V/cm at 0.25 mol%. The varistor ceramics modified with 0.05 mol% Gd₂O₃ exhibited excellent nonlinear properties, with 66.1 in the nonlinear coefficient, whereas a further increase caused it to decrease to 17.6 at 0.25 mol%. The gadolinium acted like a donor, based on the electron concentration increasing from 4.20 × 10¹⁷/cm³ to 7.38 × 10¹⁷/cm³ with an increase in the amount of Gd₂O₃.     

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.     

Microstructure and enhanced electrical properties of (1−x)(Na0.5K0.44Li0.06)NbO3–x(Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 lead-free ceramics

Environment-friendly lead-free piezoelectric ceramics (1?x)(Na_0.5K_0.44Li_0.06)NbO₃–x(Ba_0.85Ca_0.15)(Zr_0.10Ti_0.90)O₃ doped with 1.0 mol% MnO₂ were synthesized by conventional solid-state sintering method. The phase transition behavior and electrical properties of the ceramics is systemically investigated. It was found that all the ceramics formed pure perovskite phase with 0.0 ≤ x ≤ 0.1, and the phase structure of the ceramics gradually transformed from orthorhombic to tetragonal phase with increasing x. Coexistence of the orthorhombic and tetragonal phase is formed in the ceramics with 0.04 ≤ x ≤ 0.06 at room temperature, and enhanced dielectric, ferroelectric and piezoelectric properties are achieved in the two phase’s region. The ceramics in the mixed phase region exhibits the following optimum electrical properties: d ₃₃  = 130–147 pC/N, ε _r  = 642–851, P _r  = 5.51–12.44 μC/cm². The Curie temperature of the ceramics with mixed phase region was found to be 353–384 °C. The significantly enhanced dielectric properties, ferroelectric properties and piezoelectric properties with high cubic-tetragonal phase transition temperatures (T _c ) make the KNLN–xBCZT ceramics showing the promising lead-free piezoelectrics for the practical applications.     

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.     

Non-Ohmic and dielectric properties of Ba-doped CaCu3Ti4O12 ceramics

The microstructure, dielectric and electrical properties of Ca_1?x Ba _x Cu₃Ti₄O₁₂ (where x = 0, 0.025, and 0.05) ceramics were investigated. Our microstructural analyses revealed that Ba²⁺ doping ions preferentially form in a secondary phase, and are not introduced into the CaCu₃Ti₄O₁₂ lattice. Grain growth rate of CaCu₃Ti₄O₁₂ ceramics was significantly inhibited by the Ba-related secondary phase particles, resulting in a large decrease in their mean grain size. The dielectric permittivity of CaCu₃Ti₄O₁₂ ceramics decreased with increasing Ba content. Their loss tangent decreased after addition of CaCu₃Ti₄O₁₂ with 2.5 mol% of Ba²⁺, and increased with increasing Ba contents to 5.0 mol%. The nonlinear coefficient and breakdown field of the Ca_1?x Ba _x Cu₃Ti₄O₁₂ ceramics were significantly enhanced by adding 2.5 mol% of Ba²⁺, followed by a slight decrease as Ba²⁺ concentration was increased to 5.0 mol%. Using impedance spectroscopy analysis, it was revealed that variations in dielectric and non-Ohmic properties are associated with electrical response of grain boundaries. This supports the internal barrier layer capacitor model.     

Effects of MgO on properties of Li2O–Al2O3–SiO2 glass–ceramics for LTCC applications

Li₂O–Al₂O₃–SiO₂ (LAS) glass–ceramics for low temperature co-fired ceramics (LTCC) application were prepared by melting method, and the effects of MgO on the sinterability, microstructure, dielectric property, thermal expansion coefficient (CTE) and mechanical character of this glass–ceramics have been studied. The X-ray diffraction images represent that the main phase is β-spodumene solid solutions. And some ZrO₂ and CaMgSi₂O₆ phases in LAS glass–ceramics are detected. The LAS glass–ceramics without additive (MgO) sintered at 800° had the dielectric properties: dielectric constant (ε_r) of 5.3, dielectric loss (tanδ) of 2.97 × 10^?3 at 1 MHz, CTE value of 1.06 × 10^?6 K^?1, bulk density of 2.17 g/cm³, and flexural strength of 73 MPa. 5.5 wt% MgO-added LAS glass–ceramic achieves densification at 800° exhibited excellent properties: low dielectric constant and loss (ε_r = 7.1, tanδ = 2.02 × 10^?3 at 1 MHz), low CTE (2.89 × 10^?6 K^?1), bulk density = 2.65 g/cm³ as well as high flexural strength (145 MPa). The results indicate that the addition of MgO is helpful to improve the dielectric and mechanical properties. The formation of CaMgSi₂O₆ crystal phase with higher CTE leads to the increase of CTE value of LAS glass–ceramics due to the increasing MgO content, and the increase of CTE is favourable for matching with silicon (3.1 × 10^?6 K^?1). The prepared LAS glass–ceramics have the potential for LTCC application.     

Phase structures and electrical properties of LiSbO3 doped 0.994K0.5Na0.5NbO3–0.004K5.4Cu1.3Ta10O29–0.002BiMnO3 piezoelectric ceramics

LiSbO₃ (LS) doped 0.994K_0.5Na_0.5NbO₃–0.004K_5.4Cu_1.3Ta₁₀O₂₉–0.002BiMnO₃ (KNN–KCT–BM) piezoelectric ceramics with excellent properties have been fabricated by conventional ceramic processing. It is found that the dopant of LS has considerable effect on the grain size, phase structure and electrical properties of KNN–KCT–BM ceramics. The KNN–KCT–BM ceramics doped with 4.5 mol% LS ceramics show good electrical properties such as d ₃₃ = 208 pC/N, Q _m  = 95, k _p  = 40.5 %, T _c  = 335 °C, T _o?t  = 55 °C, ε _r  = 1,190 and rather low dielectric dissipation of tanδ = 1.25 % (1 kHz) and tanδ < 1 % (100 kHz). This indicates that 4.5 mol% LS-doped KNN–KCT–BM piezoceramic is an alternative lead-free piezoelectric material for the development of piezoelectric devices working at high temperature.     

Phase transition and piezoelectric properties of (1 − x)K0.5Na0.5NbO3–xLiSbO3 ceramics by hydrothermal powders

KNbO₃, NaNbO₃ and LiSbO₃ powders were synthesized by a hydrothermal route have been used to prepare (1 ? x)K_0.5Na_0.5NbO₃–xLiSbO₃ (KNN–LS; x = 0.00–0.08) ceramics. The effects of LiSbO₃ doping on the structures of KNN–LS ceramics have been systematically investigated by X-ray diffraction (XRD) and Rietveld refined XRD patterns. A gradual phase transition from orthogonal to tetragonal with the increase of LiSbO₃ content is demonstrated. Thereinto, the monoclinic phase is identified for the KNN–LS ceramic with the LiSbO₃ content of x = 0.08. Meanwhile, the XRD pattern reveals that the intensity ratio of (200)/(002) crystal face of the ceramic with x = 0.08 was bigger than one, which is different from the tetragonal phase. The tetragonal phase is revealed in the KNN–LS ceramic in the vicinity of x = 0.07, accompanying with relatively higher piezoelectric and ferroelectric properties. Tetragonal phase is beneficial to improve the piezoelectric properties of the KNN–LS ceramics.     

Dielectric properties of YSZ high-k thin films fabricated at low temperature by pulsed laser deposition

Yttria-stabilized zirconia (YSZ) films were deposited on Pt-coated silicon substrates and directly on n-type Si substrates, respectively, by pulsed laser deposition (PLD) technique using a YSZ (5 mol% Y₂O₃-stabilized ZrO₂) ceramic target. The YSZ films were deposited in 1.5×10⁻² Pa O₂ ambient at 300 °C and in situ post-annealed at 400 °C. X-ray diffraction (XRD) and differential thermal analysis measurements demonstrated that YSZ remained amorphous. The dielectric constant of amorphous YSZ was determined to be about 26.4 by measuring Pt/YSZ/Pt capacitor structure. The 6-nm-thick amorphous YSZ films with an equivalent oxide thickness (EOT) of 1.46 nm and a low leakage current of 7.58×10⁻⁵ A/cm² at 1 V gate voltage exhibit good electrical properties. YSZ thin films fabricated at low temperature 300 °C have satisfactory dielectric properties and could be a candidate of high-k gate dielectrics.     

Effect of Na/K excess on the electrical properties of Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3 thin films prepared by sol-gel processing

(Na_0.85K_0.15)_0.5Bi_0.5TiO₃ (NKBT) thin films derived from different amounts of Na/K excess content were fabricated via an aqueous sol-gel method on a Pt(111)/Ti/SiO₂/Si substrate, and the effect of Na/K excess content on the microstructure and electrical properties of the NKBT thin films was investigated. A second phase appears when Na/K excess content is below 20 mol%. Appropriated Na/K excess can enhance the polarization and dielectric properties due to compensation of Na/K loss that occurred during heat treatment. The 20 mol% excess derived NKBT thin film exhibits the best ferroelectric and dielectric properties with a remnant polarization (Pr) of 13.6 μC/cm², and a coercive field (Ec) of 104.8 KV/cm, together with a dielectric constant of 406 and a dissipation factor of 0.064. Similar to the dielectric response change with Na/K excess content, the decreasing concentration of charged defects is the main reason resulting in the increase of the piezoelectric property. The film with a 20 mol% excess content exhibited an effective d₃₃^? of about 56 pm/V. Also, the NKBT with a 20 mol% excess content exhibits the lowest current density of 5.6 × 10^− 5 A/cm² at 10 V.