Effects of Fe2O3 doping on the microstructure and piezoelectric properties of 0.55Pb(Ni1/3Nb2/3)O3-0.45Pb(Zr0.3Ti0.7)O3 ceramics

0.55Pb(Ni_1/3Nb_2/3)O₃-0.45Pb(Zr_0.3Ti_0.7)O₃(PNN-PZT) ceramics with different concentration of xFe₂O₃ doping (where x = 0.0, 0.8, 1.2, 1.6 mol%) were synthesized by the conventional solid state sintering technique. X-ray diffraction analysis reveals that all specimens are a pure perovskite phase without pyrochlore phase. The density and grain size of Fe-doped ceramics tend to increase slightly with increasing concentration of Fe₂O₃. Comparing with the undoped ceramics, the piezoelectric, ferroelectric and dielectric properties of the Fe-doped PNN-PZT specimens are significantly improved. Properties of the piezoelectric constant as high as d₃₃ ~ 956 pC/N, the electromechanical coupling factor k_p ~ 0.74, and the dielectric constant ε_r ~ 6095 are achieved for the specimen with 1.2 mol% Fe₂O₃ doping sintered at 1200 °C for 2 h.     

The effect of Sb2O5 additions on the dielectric properties of Ag(Nb0.8Ta0.2)O3 ceramics

The sintering behavior and dielectric properties for perovskite Ag(Nb_0.8Ta_0.2)O₃ ceramic with Sb₂O₅ doping was explored. A small amount of Sb₂O₅ (2.5 wt.%) led to high densification at temperatures < 1060 °C. The dielectric constant increased and the temperature coefficient decreased with increasing concentration of Sb₂O₅, and the dielectric constant reached 673, combined with a low temperature coefficient of 147 ppm/°C, and dielectric loss of 0.0044 (at 1 MHz) for the sample with 3.5 wt.% Sb₂O₅ sintered at 1080 °C.     

Enhancement microwave dielectric properties of La(Mg0.5Sn0.5)O3 ceramics by Substituting Mg for Co

The microwave dielectric properties of La(Mg_0.5−xCo_xSn_0.5)O₃ ceramics were examined with a view to exploiting them for mobile communication. The La(Mg_0.5−xCo_xSn_0.5)O₃ ceramics were prepared using the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the La(Mg_0.4Co_0.1Sn_0.5)O₃ ceramics revealed that La(Mg_0.4Co_0.1Sn_0.5)O₃ is the main crystalline phase, which is accompanied by small extent of La₂Sn₂O₇ as the second phase. Formation of this Sn-rich second phase was attributed to the loss of MgO upon ignition. Increasing the sintering temperatures seemed to promote the formation of La₂Sn₂O₇. An apparent density of 6.67 g cm⁻³, a dielectric constant (?_r) of 20.3, a quality factor (Q.F.) of 70,500 GHz, and a temperature coefficient of resonant frequency (τ_f) of −77 ppm °C⁻¹ were obtained for La(Mg_0.4Co_0.1Sn_0.5)O₃ ceramics that were sintered at 1550 °C for 4 h.     

Modified (K0.5Na0.5)(Nb0.9Ta0.1)O3 ceramics with high Qm

Lead-free ceramics (K_0.5Na_0.5)(Nb_0.9Ta_0.1)O₃ (KNNT) + x mol% K₄CuNb₈O₂₃ (KCN) + y mol% MnO₂ have been prepared using the conventional solid-state reaction technique. Crystalline structures and Microstructures were analyzed by X-ray diffraction and scanning electron microscope (SEM) at room temperature. The low dielectric loss tanδ and relatively high piezoelectric properties were obtained when KCN and MnO₂ were added into KNNT ceramics. The ceramics with x = 1.0, y = 0.50 exhibited excellent piezoelectric properties: high mechanical quality factor Q_m = 1563, piezoelectric coefficient d₃₃ = 96pC/N, electromechanical coupling coefficient k_p = 42.2%, k_t = 44.5%, k₃₃ = 58.4%, relative dielectric constant ε′ = 308, tanδ = 0.4%. This material is a promising candidate for the lead-free piezoelectric transformer applications.     

Gd2O3 doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 lead-free piezoelectric ceramics

Gd₂O₃ (0–0.8 wt.%)-doped 0.82Bi_0.5Na_0.5TiO₃–0.18Bi_0.5K_0.5TiO₃ (BNKT18) lead-free piezoelectric ceramics were synthesized by a conventional solid-state process. The effects of Gd₂O₃ on the microstructure, the dielectric, ferroelectric and piezoelectric properties were investigated. X-ray diffraction (XRD) data shows that Gd₂O₃ in an amount of 0.2–0.8 wt.% can diffuse into the lattice of BNKT18 ceramics and form a pure perovskite phase. Scanning electron microscope (SEM) images indicate that the grain size of BNKT18 ceramics decreases with the increase of Gd₂O₃ content; in addition, all the modified ceramics have a clear grain boundary and a uniformly distributed grain size. At room temperature, the ferroelectric and piezoelectric properties of the BNKT18 ceramics have been improved with the addition of Gd₂O₃, and the BNKT18 ceramics doped with 0.4 wt.% Gd₂O₃ have the highest piezoelectric constant (d₃₃ = 137 pC/N), highest relative dielectric constant (ε_r = 1023) and lower dissipation factor (tan δ = 0.044) at a frequency of 10 kHz. The BNKT18 ceramics doped with 0.2 wt.% Gd₂O₃ have the highest planar coupling factor (k_p = 0.2463).     

Synthesis of a novel langanite-type compound La3Al5.5Nb0.5O14 by the sol-gel process

Langanite (La₃Ga_5.5Nb_0.5O₁₄, LGN) and its isomorphs are a few piezoelectric materials which have the unique temperature compensation and piezoelectric properties. But the high Ga₂O₃ content makes them very expensive and limits their applications. We reported a new langanite-type compound La₃Al_5.5Nb_0.5O₁₄ (LAN) which has the advantage of no Ga₂O₃ content. Chemically homogeneous La₃Al_5.5Nb_0.5O₁₄ sol was synthesized using La (NO₃)₃·6H₂O, Al (NO₃)₃·9H₂O and niobium citrate as starting materials. Single-phased LAN powder was prepared by decomposition of a citrate polymer precursor and subsequent reactions at high temperatures. TG-DTA, XRD and FTIR were employed to investigate the transformation process of gel to LAN powder. The results showed that, after calcination at 900 °C, pure La₃Al_5.5Nb_0.5O₁₄ polycrystalline powder with a narrow particle size distribution was obtained, which has the same structure with La₃Ga_5.5Nb_0.5O₁₄.     

Silver cofirable Bi1.5Zn0.92Nb1.5O6.92 microwave ceramics containing CuO-based dopants

Bi₂O₃–ZnO–Nb₂O₅ system has emerged as a good low sintering (1050 °C) microwave material because it exhibits high dielectric constant and low temperature coefficient of resonance frequency (τ_f). We have lowered the sintering temperature of Bi_1.5Zn_0.92Nb_1.5O_6.92 (BZN) below 900 °C by using 3 wt.% of CuO-based dopants, such as 0.21BaCO₃–0.79CuO (BC) and 0.81MoO₃–0.19CuO (MC). The doped BZN exhibits high microwave dielectric constant at 2.3 GHz (k  120). The interfacial behavior between BZN and silver was investigated by using X-ray diffractometer, scanning electronic microscope, and electronic probe microanalyzer. The extent of silver migration of MC and BC dopants is reduced at least by one order of magnitude as compared with V₂O₅ dopant when the samples was prepared at 900 °C for 4 h. Thus, CuO-based dopants can replace V₂O₅ to lower the sintering temperature of BZN and to be cofired with silver.     

Topochemical synthesis of plate-like Na0.5Bi0.5TiO3 templates from Bi4Ti3O12

Plate-like templates for the development of grain oriented microstructures are required for lead-free piezoelectric ceramics with directionality of properties. Plate-like Na_0.5Bi_0.5TiO₃ templates with perovskite structure were synthesized by the Topochemical Microcrystal Conversion (TMC) method from bismuth layer-structured ferroelectric compound Bi₄Ti₃O₁₂. The TMC-derived NBT templates, with diameters of 5-15 µm and an average thickness of 0.7 µm, maintained the morphology of Bi₄Ti₃O₁₂ precursors, showing a high degree of preferred pseudocubic < 001> orientation. The Na_0.5Bi_0.5TiO₃ particles prepared could serve as good templates for the preparation of grain oriented lead-free NBT-based piezoelectric ceramics.     

Microwave dielectric and elastic properties of glass-added Ba6−3xR8+2xTi18O54 (x = 2/3)

Microwave dielectric properties of Ba_6−3xSm_8+2xTi₁₈O₅₄ (x = 2/3) [BST] ceramics with the addition of 0–3 wt.% of various glasses have been studied. It has been found that the addition of 0.5 wt.% of the glasses decreases the sintering temperature by about 150 °C. In general, addition of 0.5 wt.% of Zn, Mg and Pb-based glasses deteriorate the quality factor, whereas aluminum and barium borosilicates do not decrease it considerably. The quality factor and dielectric constant decrease with increasing amount of glass. The temperature coefficient of resonant frequency shifts towards positive or negative depending on the composition of the glass. A glass–ceramic composite with a dielectric constant 64, Q × f nearly 8500 GHz and near to zero τ_f could be obtained at a sintering temperature of 1175 °C when 3–4 wt.% Al₂O₃–B₂O₃–SiO₂ glass was added to BST ceramic. The Young's modulus decreases with increasing amount of glass, irrespective of the composition of glass.     

The study on electrical behavior of Gd2O3-WO3 complex ceramics at high temperature

Gd₂O₃-WO₃ complex ceramics are fabricated by the conventional solid-state reaction process. The electrical characteristics and dielectric properties of the samples were measured at various ambient temperatures in a low electric field (E < 150 V/mm). As the temperature increases, the dielectric constant and the loss tangent show an obvious change at about 50 °C and 330 °C. When the temperature is above 200 °C, the samples display stable nonlinear electrical properties characterized by semiconductivity, and the nonlinearity increases along with increasing temperature. XRD analysis reveals that Gd₂W₂O₉ is the main phase and Gd₂O₃ is the secondary phase. Based on the phase transition of tungsten trioxide, these electrical properties of Gd₂O₃-WO₃ complex ceramics can be simply explained.     

Improved dielectric properties of CaCu3Ti4O12 thin films on oxide bottom electrode of La0.5Sr0.5CoO3

We report on the effect of La_0.5Sr_0.5CoO₃ (LSCO) bottom electrode to the dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) thin films grown on Ir/Ti/SiO₂/Si substrates. Compared with the films grown directly on Ir/Ti/SiO₂/Si substrates, the dielectric constant has been increased greatly about 100%, and the dielectric loss decreased to lower than 0.2 in the frequency range of 1-100 kHz. The origin has been discussed in details based on the analysis of the X-ray diffraction and impedance spectra measurements. Results of the impedance spectra suggest that the absence of undesired interfacial layer between Ir/CCTO thin films might be one of the major reasons of the improvement of the dielectric properties when the LSCO was introduced as the bottom electrode.     

Enhanced temperature stability of modified (K0.5Na0.5)0.94Li0.06NbO3 lead-free piezoelectric ceramics

To improve both the temperature stability and the mechanical quality factor of (K_0.5Na_0.5)_0.94Li_0.06NbO₃ (KNLN6) ceramics, dense (K₄CuNb₈O₂₃, Bi₂O₃)-modified KNLN6 lead-free ceramics were prepared. Results showed that the (K₄CuNb₈O₂₃, Bi₂O₃)-modified ceramics exhibited a flat, temperature-stable behavior over the range of 20–120 °C. K₄CuNb₈O₂₃ (KCN) and Bi₂O₃-codoping changed the KNLN6 to “hard” ceramics with a significant improvement of mechanical quality factor, Q _m, from 82 to 756. Meanwhile, the piezoelectric constant, d ₃₃, and the planar electromechanical coefficient, k _p, still maintained relatively high levels (d ₃₃ ~118 pC/N, k _p ~35.6%). These results indicate that the modified KNLN6 ceramics are promising lead-free piezoelectric candidates for practical applications.     

Effect of CuO addition to Nd(Zn1/2Ti1/2)O3 ceramics on sintering behavior and microwave dielectric properties

The microwave dielectric properties and microstructures of CuO-doped Nd(Zn_1/2Ti_1/2)O₃ ceramics prepared by the conventional solid-state route were investigated. The prepared Nd(Zn_1/2Ti_1/2)O₃ exhibits a mixture of Zn and Ti showing 1:1 order in the B-site. As an appropriate sintering aid, not only did CuO lower the sintering temperature, it could effectively hold back the evaporation of Zn in the Nd(Zn_1/2Ti_1/2)O₃. Moreover, CuO only resided in boundaries, which was confirmed by EDX analysis. The measured lattice parameters of CuO-doped Nd(Zn_1/2Ti_1/2)O₃ (a = 5.4652 ± 0.0005 ?, b = 5.6399 ± 0.0007 ?, c = 7.7797 ± 0.0008 ? and β = 90.01 ± 0.01°) retained identical to that of the pure Nd(Zn_1/2Ti_1/2)O₃ in all cases. In comparison with the pure Nd(Zn_1/2Ti_1/2)O₃ ceramics, specimen with 1 wt.% CuO addition possesses a compatible combination of dielectric properties with a ε_r of 30.68, a Q × f of 158,000 GHz (at 8 GHz) and a τ_f of − 45 ppm/°C at 1270 °C. It also indicated a 60 °C lowering in the sintering temperature. The proposed dielectrics can be a very promising candidate material for microwave or millimeter wave applications requiring extremely low dielectric loss.     

Effects of Bi2O3 and Cr2Ti3O9 Co-doping on dielectric properties in BaTiO3-based ceramics

A microwave ceramic with general composition (1-x-y) BaTiO₃ + x Cr₂Ti₃O₉ + y Bi₂O₃ has been prepared by solid state synthesis at 1300-1400 °C. The phase composition, perovskite structural parameters and dielectric properties have been obtained by X-ray diffraction and dielectric measurements as a function of chemical composition and temperature. At low doping levels the formation of BaTiO₃-based solid solution has been found. The precipitation of BaCrO₃ has been detected at x = y = 2.0 mol%. A model of the incorporation of Cr³⁺ and Bi³⁺ ions into BaTiO₃-based crystal lattice has been proposed. Diffused phase transition in the temperature range 100-140 °C have been revealed by dielectric measurements for different ceramic composition. As high dielectric constant as 7311 and as low dielectric loss as 0.02 have been found for the composition of 0.98BaTiO₃-0.01Cr₂Ti₃O₉-0.01Bi₂O₃.     

Influence of ZnO additions to 0.8(Mg0.95Co0.05)TiO3–0.2Ca0.6La0.8/3TiO3 ceramics on sintering behavior and microwave dielectric properties

The effects of ZnO addition on the microstructures and microwave dielectric properties of 0.8(Mg_0.95Co_0.05)TiO3–0.2Ca_0.6La_0.8/3TiO₃ ceramics were investigated. ZnO was selected as liquid phase sintering aids to lower the sintering temperature of 0.8(Mg_0.95Co_0.05)TiO3–0.2Ca_0.6La_0.8/3TiO₃ ceramics. With ZnO additives, the densification temperature of 0.8(Mg_0.95Co_0.05)TiO₃–0.2Ca_0.6La_0.8/3TiO₃ can be effectively reduced from 1450 to 1200–1325 °C. The crystalline phase exhibited no phase difference at low addition levels (0.25–2 wt.%). It is found that low-level doping of ZnO (0.25–2 wt.%) can significantly improve the density and dielectric properties of 0.8(Mg_0.95Co_0.05)TiO₃–0.2Ca_0.6La_0.8/3TiO₃ ceramics. The quality factors Q × f were strongly dependent upon the amount of additives. Q × f values of 36 000 and 13 000 GHz could be obtained at 1200–1325 °C with 1 and 2 wt.% ZnO additives, respectively. During all additives ranges, the relative dielectric constants were significantly different and ranged from 23.1 to 27.96. The temperature coefficient varies from 14.1–24.3 ppm/°C.     

Dielectric and piezoelectric properties of Y2O3 doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free piezoelectric ceramics

Y₂O₃ doped lead-free piezoelectric ceramics (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (0-0.7 wt%) were synthesized by the conventional solid state reaction method, and the effect of Y₂O₃ addition on the structure and electrical properties was investigated. X-ray diffraction shows that Y₂O₃ diffuses into the lattice of (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ to form a solid solution with a pure perovskite structure. The temperature dependence of dielectric constant of Y₂O₃ doped samples under various frequencies indicates obvious relaxor characteristics different from typical relaxor ferroelectric and the mechanism of the relaxor behavior was discussed. The optimum piezoelectric properties of piezoelectric constant d₃₃ = 137 pC/N and the electromechanical coupling factor k_p = 0.30 are obtained at 0.5% and 0.1% Y₂O₃ addition, respectively.     

Ferrimagnetic and semiconducting CaCu3Fe2Sb2O12 by first principles

CaCu₃Fe₂Sb₂O₁₂ is mechanically stable, thermodynamically stable at pressures above 18 GPa. Both GGA and GGA + U methods predict that it is a ferrimagnetic semiconductor with Fe³⁺ in high spin state (S = 5/2). The coupling of Fe–Cu is antiferromagnetic, while that of Cu–Cu is ferromagnetic. The calculated total spin moment is 6.17 μ_B.     

Synthesis of CaCu3Ti4O12 ceramic via a sol-gel method

The novel nano-ultrafine powders for the preparation of CaCu₃Ti₄O₁₂ ceramic were prepared by the sol-gel method and citrate auto-ignition method. The obtained precursor powders were pressed, sintered at 1000 °C to fabricate microcrystal CaCu₃Ti₄O₁₂ ceramic. The microcrystalline phase of CaCu₃Ti₄O₁₂ was confirmed by X-ray powder diffraction (XRD). The morphology and size of the grains of the powders and ceramics under different heat treatments were observed using scanning electron microscopy (SEM). The relative dielectric constant of the ceramic sintered at 1000 °C was measured with a magnitude of more than 10⁴ at room temperature, which was approaching to those of Pb-containing complex perovskite ceramics, and the loss tangent was less than 0.20 in a broad frequency region. The relative dielectric constant and loss tangent were also compared with that of CaCu₃Ti₄O₁₂ ceramic prepared by other reported methods.     

Effect of Ca Substitution on the Superconductivity of La2.5Y0.5CaBa3(Cu0.88Fe0.12)7Oz

The structural and superconducting properties of single-phase La_2.5–y Y_0.5Ca_1+y Ba₃ (Cu_0.88Fe_0.12)₇O _z (LYCaBCuFe) (y= 0.0–1.0) compounds with triple perovskite structure are investigated using X-ray diffraction, resistivity, a.c. susceptibility, and oxygen content measurements. Increasing Ca substitution for La resulted in a decrease in unit cell axes and volume. T _c ^R=0 shows a marginal increase from 31 K to 37 K for y = 0.0–0.21 and thereafter it decreases with increasing y leading to zero T _c ^R=0 at y 0.84. This shows that the suppression of T _c from 80 K to 31 K by Fe doping at x = 0.12 La_2.5Y_0.5CaBa₃(Cu_1–x Fe _x )₇O _z cannot be compensated by appropriate hole doping with Ca in LaYCaBCuFe.     

Microwave dielectric properties of Li2TiO3 ceramics sintered at low temperatures

Li₂TiO₃ ceramics were prepared at the sintering temperatures from 1050 to 1250 °C. The optimal microwave dielectric properties were ?_r = 23.29, Q × f = 15,525 GHz (5.9 GHz), and τ_f = 35.05 ppm/ °C for the sample sintered at 1200 °C. The microwave dielectric properties were improved obviously when the Li₂TiO₃ ceramics were sintered at low temperatures with small additions of H₃BO₃ (B₂O₃ in the form of H₃BO₃). Only monoclinic Li₂TiO₃ was found in the pure or H₃BO₃-doped Li₂TiO₃ ceramics. About 1.0 wt.% H₃BO₃ addition aided the sintering of Li₂TiO₃ ceramics effectively while excessive H₃BO₃ (≥2.5 wt.%) was not favorable. Typically the best microwave dielectric properties were ?_r = 23.28, Q × f = 37,110 GHz (6.3 GHz), and τ_f = 30.43 ppm/ °C for the 1.0 wt.% H₃BO₃-doped Li₂TiO₃ ceramic sintered at 920 for 3 h, which is promising for LTCC applications.