Effect of micro-region heterogeneity on phase structure and dielectric properties in Pb(Zn1/3Nb2/3)O3–PbTiO3–BaTiO3 ceramics

The phase structures of PZN-PT-BT ceramics under different synthesizing steps and thermal treatment were investigated. Although the calcinated powders (C.T. = 900 °C) of the compositions in tetragonal area exhibit pure tetragonal structure, the phase structures of the ceramics sintering at higher temperatures (S.T. 1080 °C) are the mixtures of tetragonal and rhombohedral. The content of tetragonal phase in PZN-PT-BT ceramics decreases further after the specimens are annealed. Dielectric and ferroelectric properties were studied. The annealed ceramics have higher average phase transition temperatures, lower frequency dispersions, lower dissipation factors and larger aging rates. The maximum of the dielectric constant and the spontaneous polarization at room temperature are almost unaffected by annealing process. The concept of nano-phase separation is assumed to explain the experimental results.     

Enhanced thermal stability and large piezoelectric properties of Sm-doped Pb(Sc1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 multifunctional ceramics

Journal of Materials Science - The crystal structure, electric properties, thermal stability and optical properties of Sm-doped 0.15Pb(Sc1/2Nb1/2)O3–0.50Pb(Mg1/3Nb2/3)O3–0.35PbTiO3...     

Dielectric and electromechanical properties of Mn-doped 0.2875 Pb(Mg1/3Nb2/3)O3–0.2875 Pb(Yb1/2Nb1/2)O3–0.425 PbTiO3 ceramics

In this study, 0.2875 Pb(Mg_1/3Nb_2/3)O₃–0.2875 Pb(Yb_1/2Nb_1/2)O₃–0.425 PbTiO₃ (0.2875PMN–0.2875PYbN–0.425PT) ternary ceramic composition was doped with 1 mol% MnCO₃ in order to induce hard character for potential high-power applications. Dense 0.2875PMN–0.2875PYbN–0.425PT ceramics with 1 mol% MnCO₃ addition were fabricated after sintering at 1100 °C. ε _r = 1728, tanδ = 0.35 %, d ₃₃ = 320 pC/N, d ₃₁ = ?103 pC/N, Q _m = 467, k _p = 0.40, k ₃₁ = 0.24, k ₃₃ = 0.49, and T _c = 280 °C were measured for Mn-doped ceramics. However, undoped ceramics had ε _r = 2380, tanδ = 1.95 %, d ₃₃ = 433 pC/N, d ₃₁ = ?145 pC/N, Q _m = 60, k _p = 0.43, k ₃₁ = 0.27, k ₃₃ = 0.48, and T _c = 285 °C. Acceptor Mn²⁺/Mn³⁺ ions presumably substituted B-site ions in the perovskite structure and formed defect dipole pairs. The electrically “hard” character was induced as a result of the domain wall pinning due to the existing defect pairs. Particularly, increasing Q _m from 60 to 467 and decreasing tanδ from 1.95 to 0.35 % after Mn doping showed that Mn-doped 0.2875PMN–0.2875PYbN–0.425PT ceramics with “hard” character are potential candidates for high-power projector and transducer applications.     

Effect of La on piezoelectric properties of Pb(Ni1/3Sb2/3)O3–Pb(ZrTi)O3 ferroelectric ceramics

Piezoceramic compositions Pb_1?zLa_z(NiSb)_0.05[(Zr_0.52Ti_0.48)_1?Z/4]_0.95O₃ with Z = 0.01–0.05 were synthesized by mixed oxide route to study the effect of Lanthanum (La) on crystal structure, microstructure, piezoelectric and ferroelectric properties. Calcination was performed at 1,060 °C and sintering at 1,270 °C for 1 h. X-Ray diffraction pattern indicated the polycrystalline microstructure along with co-existence of tetragonal and rhombohedral perovskite phases. Dielectric constant ( $ K_{3}^{T} $ ) was increased whereas piezoelectric voltage constant (g ₃₃) was decreased with increase in lanthanum. Dense microstructure was observed for the composition containing 3 mol% of lanthanum. This was resulted in optimum piezoelectric charge constant (d ₃₃ = 468 × 10^?12 C/N), electromechanical coupling factor (k _p  = 0.68), remanent polarization (P _r = 24.65 μC/cm²) and displacement (D = 2,012 nm). Results indicated that the composition Pb_0.97La_0.03(NiSb)_0.05[(Zr_0.52Ti_0.48)_0.9925]_0.95O₃ could be suitable for actuator applications. The composition Pb_0.98La_0.02(NiSb)_0.05[(Zr_0.52Ti_0.48)_0.995]_0.95O₃ resulted into moderately high value of voltage constant (g ₃₃ = 39.3 × 10^?12 V m/N) and optimum value of Figure of Merit (d ₃₃ × g ₃₃ = 16.2 × 10^?12 C V m/N²) indicated the usefulness for sensor and power harvesting applications.     

Dielectric and Piezoelectric Properties of Pb(Mg1/3Nb2/3)O3–PbTiO3–Pb(Mg1/2W1/2)O3 Ceramics

Data are presented on the phase composition, crystal structure, microstructure, and dielectric and piezoelectric properties of (1 – y)[(1 – x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃]–yPb(Mg_1/2W_1/2)O₃ (x = 0.30–0.36; y = 0, 0.05, 0.10) ceramics. It is shown that the use of fine-particle magnesia as a starting reagent ensures the formation of single-phase materials. The ceramics with a rhombohedral structure are found to exhibit relaxor behavior. Increasing the content of the Pb(Mg_1/2W_1/2)O₃ perovskite leads to ordering of the domain structure of poled ceramics and increases their piezoelectric charge coefficient d ₃₁ and the width of their phase transitions.     

Microstructure and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3–MgO composite ceramics with nano-silica added

Ba(Mg_1/3Nb_2/3)O₃–MgO composite ceramics were prepared by solid-phase method. The ceramic exhibited the 1:2 ordered structure. By adding a proper amount of MgO, the permittivity decreased rapidly compared with other Ba(Mg_1/3Nb_2/3)O₃-based ceramics. The Q?×?f values of the samples were greatly improved by nano-silica. Raman spectra showed that the permittivity and Q?×?f value showed a strong correlation with Raman shift and full width at half maximum of the A_1g(O) phonon mode, respectively. The Raman shift of A_1g(O) was consistent with the variation trend of permittivity. And the full width at half maximum of the A_1g(O) phonon mode had a negative correlation with the Q?×?f value. The results showed that upon adding 1.5 wt% nano-silica to the ceramics, the ceramics sintered at 1550 °C for 5 h had the lowest Raman shift and the narrowest full width at half maximum, achieving the best microwave dielectric properties: ε_r?=?22.22, Q?×?f?=?80,436 GHz, τ_f?=?–?5.89 ppm/°C.

     

Electrocaloric properties of (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 ferroelectric ceramics near room temperature

Electrocaloric effects of (1 − x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃ [abbreviated as (1 − x)PMN–xPT] ferroelectric ceramics with x being, 0.08, 0.10, and 0.25, respectively, were measured near room temperature, and the origins of the electrocaloric effects of these ceramics were discussed. It was found that these ceramics possess large electrocaloric effect with ΔT being, more than 1 K under an electric field of 1.5 kV mm⁻¹ in a wide temperature range (more than 10 K) near room temperature, and this effect is due to both of the electrocaloric effect resulting from the electric field induced first-order phase transition and the linear electrocaloric effect. It is expected that these ceramics could be used for multi-stage cascade ferroelectric refrigeration near room temperature.     

Low-temperature sintering and piezoelectric properties of Pb(Fe2/3W1/3)O3–added Pb(Zn1/3Nb2/3)O3–Pb(Ni1/3Nb2/3)O3–Pb(Zr,Ti)O3 ceramics

Low-temperature sintering of (a–x)Pb(Zr_0.48Ti_0.52)O₃–bPb(Ni_1/3Nb_2/3) O₃–cPb(Zn_1/3Nb_2/3)O₃–xPb(Fe_2/3W_1/3)O₃ (a + b + c + x = 1, 0.06 ≤ x ≤ 0.10) ceramics were prepared through two-step synthesis process using perovskites-structured ferroelectric materials Pb(Fe_2/3W_1/3)O₃ (PFW) as a sintering aid. The effects of PFW content on the densification, microstructure, phase structure, dielectric and piezoelectric properties of the ceramics were investigated. The sintering temperature was reduced from 1,180 °C (without PFW addition) to 940 °C when the material was PFW-doped. PFW-doping increased the sintered density and the average grain size of PFW–PNN–PZN–lead zirconate titanate ceramics. The ceramics sintered at 940 °C for 4 h with x = 0.08 exhibited favorable properties, which were listed as follows: d₃₃ = 496pC/N, εT 33/ε₀ = 3,119, tanδ = 2.1 % and Curie temperature = 242 °C. These values indicated that the newly developed composition might be suitable for multilayer piezoelectric devices application.     

Effect of sintering parameters on the microstructure and microwave dielectric properties of Ba(Zn1/3Nb2/3)O3–ZnNb2O6 Ceramics

Ba(Zn_1/3Nb_2/3)O₃–ZnNb₂O₆(BZNZ) composite ceramics were fabricated by conventional solid solution processing. After optimizing the composition, the effects of the sintering parameters, such as the heating rate, the soaking time, and the cooling rate on densities, microstructure, and microwave dielectric properties were investigated using orthogonal experimental design method. The results show that with increasing the content of Ba(Zn_1/3Nb_2/3)O₃, the ε _r increases, while the Q × f value increases first, then decreases, and τ _f shifts to the negative value. The BZNZ ceramics with composition of 0.3Ba(Zn_1/3Nb_2/3)O₃–0.7ZnNb₂O₆ show the optimal dielectric properties. The results of orthogonal experimental design show that sintering parameters play an important role in the microstructure and dielectric properties. The ceramics show obvious duplex-grain structure. The importance sequence of the sintering parameters is: cooling rate > heating rate > soaking time. The sintering parameters were optimized, with 0.3Ba(Zn_1/3Nb_2/3)O₃–0.7ZnNb₂O₆ ceramic sintered at a heating rate of 2 °C/min, soaking time of 8 h, and cooling in the air. Samples have the excellent dielectric properties: ε_r = 32.75, Q × f = 34,100, and τ _f  = ?10.2 ppm/°C.     

Sintering and electrical properties of Nb5+ doped 0.63Bi(Mg1/2Ti1/2)O3–0.37PbTiO3 piezoelectric ceramics

Nb⁵⁺ doped 0.63Bi(Mg_1/2Ti_1/2)O₃–0.37PbTiO₃ (0.63BMT–0.37PT?+?xNb⁵⁺) ceramics have been fabricated by means of citrate sol–gel method and ordinary sintering. Effects of Nb⁵⁺ doping on the densification and various electrical properties were studied. The results indicated that the addition of a small amount of Nb⁵⁺ gradually changes the crystal structure from a typical rhombohedral-tetragonal coexisted structure to a nearly pure rhombohedral structure. A slight amount of secondary phases start to appear as the doping content of Nb⁵⁺ is more than 1.5?mol%, indicating that the solubility limit of Nb⁵⁺ in the matrix composition is reached. Moreover, electrical properties of the sintered ceramics were obviously changed based on the effect of densification and ionic substitution. 0.63BMT–0.37PT?+?0.005Nb⁵⁺ ceramics sintered at 1,020?°C exhibit optimum properties of piezoelectric constant d₃₃?~?245 pC/N, planar electromechanical coupling factor k_p?~?30?%, $ \varepsilon_{33}^{\text{T}} /\varepsilon_{\text{o}} $ ?~?1,220, and T_c?~?460?°C.     

Preparation and dielectric properties of Pb[(Zn1/3Ta2/3)0.8−x(Mg1/3Nb2/3)xTi0.2]O3 ceramics

A PbTiO₃ component of 20 mol% was substituted into a Pb[(Zn_1/3Ta_2/3),(Mg_1/3Nb_2/3)]O₃ system to promote the perovskite formation, especially at Pb(Zn_1/3Ta_2/3)O₃-rich compositions. Perovskite formation yields after the heat treatments were determined by X-ray diffraction. Weak-field dielectric properties of the ceramics were investigated as functions of temperature and frequency. A quite high value of the maximum dielectric constant (37,900 at 1 kHz) was realized, whereas the dielectric maximum temperatures of the entire compositions stayed nearly constant. Microstructure developments in the sintered ceramics were also examined.     

Effect of La2O3 additive on the dielectric properties of barium strontium titanate glass–ceramics

The barium strontium titanate (Ba_xSr_1–xTiO₃) glass–ceramics doped with different content of La were prepared via controlled crystallization. Phase compositions, microstructure and dielectric behaviors were investigated systematically. The results revealed that La₂O₃ additives had little influence on the dielectric constant but significantly changed the microstructure of the glass–ceramics, which led to improved breakdown strength (BDS). The optimized energy-storage density of 3.18 J/cm³ was achieved in the glass–ceramics with 1.0 wt% La₂O₃ content which is 2.56 times higher than pure BST glass–ceramics, suggesting glass–ceramics of this composition could be an attractive candidate for energy-storage applications.     

Investigation of phase diagram and electrical properties of xPb(Mg1/3Nb2/3)O3–(1 − x)Pb(Zr0.4Ti0.6)O3 ceramics

Ceramics in PMN–PZT system with formula xPb(Mg_1/3Nb_2/3)O₃–(1 ? x)Pb(Zr_0.4Ti_0.6)O₃ (where x = 0.32, 0.35, 0.38, 0.41) were prepared by the conventional oxide-mixed method. The phase diagram, composition dependent ferroelectric, dielectric, field-induced strain and piezoelectric properties were systematically investigated. X-ray diffraction analysis indicated that as-prepared ceramics were of pure perovskite phase and the possible morphotropic phase boundary (MPB) between the tetragonal and pseudo-cubic phase compositions were located near the PMN content of x = 0.38, confirmed by their corresponding ferroelectric, dielectric, field-induced strain and piezoelectric properties. The composition with x = 0.38 possessed the optimum electrical properties since its composition locate close to the MPB where exist multiple polarization directions facilitates domain reorientation and consequently enables the superior electrical properties. The room temperature dielectric permittivity ε _r , tangent loss tan δ, piezoelectric coefficient d ₃₃, electromechanical coupling factor kp, remnant polarization P _r , hysteresis loop squareness R _sq and longitudinal strain of 0.38PMN–0.62PZT ceramics are 2441, 2.08 %, 662 pC/N, 63.5 %, 37.2 μC/cm², 1.51 and 1.9 ‰, respectively, which mean it has a great promise for actuator applications.     

Microwave dielectric properties of CaO–La2O3–Nb2O5–TiO2 ceramics

A series of ceramics with a general formula Ca_1+xLa_4?xNb_xTi_5?xO₁₇ (0 ≤ x ≤ 4) were fabricated using the solid-state ceramic route. The phase, microstructure, and microwave dielectric properties varied distinctly with composition or the value of x. X-ray diffraction results showed that the two end member phases, CaLa₄Ti₅O₁₇ and Ca₅Nb₄TiO₁₇, crystallized into single phases with orthorhombic and monoclinic crystal structure, respectively. For intermediate compounds with x = 1, 2, and 3, mixture phases CaLa₄Ti₅O₁₇ and Ca₅Nb₄TiO₁₇ coexisted and a trace amount of second phase was detected. The ceramics showed high ε _r in the range of 45–52, relatively high quality factors with Q × f in the range of 9,870–15,680 GHz and τ _f value in the range between ?38 and ?126.4 ppm/°C. τ _f of CaLa₄Ti₅O₁₇ can be tuned to a near-zero value by addition of suitable amount of TiO₂.     

Microwave dielectric properties and applications of Ba(Zn1/3Nb2/3)O3–Ca(Zn1/3Nb2/3)O3 composite ceramics by one-step synthesis method

(1 ? x) Ca(Zn_1/3Nb_2/3) O₃ ? xBa(Zn_1/3Nb_2/3)O₃ (short for CZN/BZN, x = 0–1.0) ceramics were prepared and investigated through the “one-step synthesis method” method. The structure of the system was analyzed using X-ray diffraction. The microstructure of the sintered pellet was analyzed using scanning electron microscopy. Dielectric constant (ε_r), temperature coefficient of resonant frequency (τ_f) and the unloaded quality factor (Q × f) were measured in the microwave frequency region. Two dielectric properties were firstly in the rising tendency and then decreasing with the increased x. On the other hand, a good combination of microwave dielectric properties (ε_r = 24, Q × f = 23,510 GHz τ_f = ?9 ppm/°C) were obtained at x = 0.1. The compositions have excellent microwave dielectric properties and hence are suitable for ceramic capacitors or dielectric resonators applications.     

Processing and electrical properties of (1 − x)[(1 − y)(Pb(Mg1/3Nb2/3)O3)–y(Pb(Yb1/2Nb1/2)O3)]–xPbTiO3 ceramics

Ferroelectric ceramics in the vicinity of morphotropic phase boundary (MPB) with compositions represented as (1 ? x)[(1 ? y)(Pb(Mg_1/3Nb_2/3)O₃)–y(Pb(Yb_1/2Nb_1/2)O₃)]–xPbTiO₃ were prepared by solid state reaction. The addition of PYbN to PMN–PT decreased the sintering temperature from 1200 °C (y = 0.25) to 1000 °C (y = 0.75). The PT content, where the MPB was observed, increased with the PYbN addition. A remanent polarization value of 28.5 µC/cm² and a coercive field value of 11 kV/cm were measured from 0.62[0.25PMN–0.75PYbN]–0.38PT ceramics, which were close to the ones measured from PMN–0.32PT ceramics. In addition, the Curie temperature was found to increase with PYbN additions.     

Microwave dielectric properties and microstructures of Ca(Nb1−xTax)2O6 ceramics

This study elucidates the microwave dielectric properties and microstructures of Ca(Nb_1?xTa_x)₂O₆ ceramics with a view to their potential for microwave devices. The Ca(Nb_1?xTa_x)₂O₆ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Ca(Nb_0.93Ta_0.07)₂O₆ ceramics revealed no significant variation of phase with sintering temperatures. A dielectric constant (? _r ) of 17.7, a quality factor (Q × f) of 117,000 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?51 ppm/°C were obtained for Ca(Nb_0.93Ta_0.07)₂O₆ ceramics that were sintered at 1,400 °C for 4 h.     

Effects of SrO–B2O3–SiO2 glass additive on dielectric properties of Ba(Fe0.5Nb0.5)O3 ceramics

SrO–B₂O₃–SiO₂ (SBS) glass powders were prepared and employed as sintering aids to reduce the sintering temperature of Ba(Fe_0.5Nb_0.5)O₃ (BFN) ceramics. The effects of glass content on the dielectric properties and breakdown strength of BFN ceramics have been investigated. The volume density characterization results of (1 ? x) BFN ? x SBS ceramics indicate that the sintering temperature of BFN ceramics decreased by 200–350 °C with SBS glass addition (when x = 0, 0.01, 0.03 and 0.05). The XRD patterns show BFN ceramics indicate cubic crystal structure and without the formation of a secondary phase. The dielectric constant and dielectric loss decreased gradually with increasing glass content, and the dielectric loss decreased by one order of magnitude with SBS glass addition (when x = 0.05). The breakdown strength of (1 ? x) BFN ? x SBS ceramics increase with increasing glass content, in which is about 33.90 kV/cm with SBS glass addition (when x = 0.05). These improvements in the dielectric characteristics of BFN ceramics have great scientific significance for their applications.