Reaction sintering and characterization of lead magnesium niobate relaxor ferroelectric ceramics

The formation and densification of Pb(Mg_1/3Nb_2/3)O₃ ceramics prepared by reaction sintering have been investigated. Two kinds of lead sources. PbO and Pb₃O₄ are used as the starting materials for Pb(Mg_1/3Nb_2/3)O₃. During heating processes, the specimens first expand while the pyrochlore phase is formed. At elevated temperatures, the formation and rapid sintering of Pb(Mg_1/3\Nb_2/3)O₃ occur simultaneously. The starting materials of the Pb₃\O₄ system exhibit better reactivity and sinterability than those of the PbO system. With Pb₃\O₄ as the starting material, monophasic Pb(Mg_1/3\Nb_2/3)O₃ ceramics with high sintering density are successfully achieved by reaction sintering at as low as 900 °C. While for the PbO system, pure perovskite phase could not be synthesized because of the existence of residual pyrochlore phase, and the ceramics obtained have low sintering density. The dielectric permittivity of the Pb(Mg_1/3Nb_2/3)O₃ ceramics obtained in the Pb₃O₄ system is higher than that in the PbO system. This is attributed to the formation of pure perovskite phase and high sintering density in the former system.     

Preparation and dielectric properties of Pb(Zn1/3Nb2/3)O3-based ferroelectric ceramics

The sintering behavior of mechanochemically prepared 0.9Pb(Zn_1/3Nb_2/3)O₃-0.1ABO₃ (ABO₃ = BaBiO₃, BaMnO₃, BaTiO₃) powders is studied. PbO and Bi₂O₃ are shown to volatilize at relatively low temperatures owing to partial reduction of these oxides during the mechanochemical synthesis. Dense (97% of theoretical density) ceramics are obtained under mild sintering conditions, and their dielectric properties are studied at different frequencies. The observed variations of their dielectric permittivity and loss tangent with frequency are typical of relaxor ferroelectrics, but the ceramics have a reduced dielectric permittivity, which is attributable to nanostructuring.     

A-site deficient perovskites Ba(M2+ 1/3Nb2/3)O3: microstructural attributes for a high quality factor

Slight A-site deficiency in ordered perovskites Ba(M²⁺ _1/3Nb_2/3)O₃(M - Co, Zn, Mg) is shown to promote the formation of single-phase dense ceramics, in which the microwave (MW) quality factor Q attains its maximum values. Any further decrease in the Ba concentration in Ba(M²⁺ _1/3Nb_2/3)O₃ always results in the formation of a multiphase material containing secondary phase with the tetragonal tungsten bronze (TTB) structure. The amount of TTB phase in the perovskite matrix was found to depend on both the Ba concentration and the sintering temperature. The composition and properties of the TTB phase are discussed in terms of their effect on the MW dielectric parameters of Ba(M²⁺ _1/3Nb_2/3)O₃ ceramics.     

Fabrication and dielectric properties of textured Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-BaTiO<Subscript>3</Subscript> ceramics by RTGG method

Grain-oriented Na_0.5Bi_0.5TiO₃-BaTiO₃ (NBTBT) ceramics were fabricated by reactive-templated grain growth using plate-like Bi_2.5Na_3.5Nb₅O₁₈ (BNN) as templates. The specimens are composed of NBTBT perovskite phase and BNN lay-structured phase. Textured ceramics have a brick-wall microstructure with strip-like grains aligning in the direction parallel to the casting plane and exhibit an {h00} preferred orientation. The texture fraction increases initially, and then decreases with increasing sintering temperature. The optimal sintering temperature is 1,185 °C where the texture fraction has a maximum value of 0.58 and d₃₃ is 98 pC/N. The textured NBTBT ceramics show evidence of relaxor ferroelectrics with diffuse phase transition and frequency dispersion because of composite biphasic structure.     

Mechanochemical synthesis, phase composition, and properties of Pb(Zn1/3Nb2/3)O3-based ferroelectric ceramics

Pb-containing relaxor ferroelectric ceramics are prepared by mechanochemical ceramic processing. Mechanochemical reactions in binary and ternary mixtures of the PbO-ZnO-Nb₂O₅ system are studied by x-ray diffraction. Disordered compounds with the columbite, changbaiite, and pyrochlore structures are prepared. The perovskite and pyrochlore phases in 0.9Pb(Zn_1/3Nb_2/3)O₃ + 0.1ABO₃ morphotropic phase boundary materials are shown to be in mechanochemical equilibrium. Among the ABO₃ additives studied, BaMnO₃ is the most effective for stabilizing the perovskite structure. The mechanochemical synthesis path has a strong effect on the phase composition of the resulting material. Conventional synthesis through a columbite phase leads to the predominant formation of a pyrochlore phase. Firing conditions also have a profound effect on the phase composition of the ceramics, but the disordered perovskite phase retains cubic symmetry.     

Microstructure and microwave dielectric properties of multi-oxide-doped (Zr,Sn)TiO4 ceramics

(Zr_0.8Sn_0.2)TiO₄ (ZST) ceramics were prepared by solid-phase method. The effects of MgO/La₂O₃/Nb₂O₅ doped on the phase composition, microstructure, sintering behavior, and microwave dielectric properties of ZST ceramics were investigated. XRD analysis showed that the major crystalline phase was ZST. Very small amounts of phases, Nb₂O₅ and Mg(Ti₂O₅), were observed when dopants were added, and Nb₂O₅ inhibited the formation of Mg(Ti₂O₅). The results showed that upon adding 7 wt% Nb₂O₅ and small amounts of MgO and La₂O₃ to the ceramics, the permittivity of the ceramics was greatly reduced compared to that of other oxide-doped (Zr_, Sn)TiO₄ ceramic materials, and the Q?×?f value was also increased. The coefficients of thermal expansion of ZST ceramics in this study were within the range reported in the literature. Optimal dielectric properties, ε_r?=?34.78, Q?×?f?=?55,190 GHz (f?=?5.8 GHz), τ_f?=?? 13.86 ppm/°C, and CTE?=?7.0 ppm/°C, were achieved for the sample with 7 wt% Nb₂O₅ sintered at 1330 °C for 2 h.

     

Stoichiometric Pb(Mg1/3Nb2/3)O3 perovskite ceramics produced by reaction-sintering process

Stoichiometric lead magnesium niobate, Pb(Mg_1/3Nb_2/3)O₃ (PMN), perovskite ceramics produced by reaction-sintering process were investigated. Without calcination, a mixture of PbO, Nb₂O₅, and Mg(NO₃)₂ was pressed and sintered directly. Stoichiometric PMN ceramics of 100% perovskite phase were obtained for 1, 2, and 4 h sintering at 1250 and 1270 °C. PMN ceramics with density 8.09 g/cm³ (99.5% of theoretical density 8.13 g/cm³) and K_max 19,900 under 1 kHz were obtained.     

Preparation,characterization, electrical properties and giant dielectric response in (In + Nb) co-doped TiO<Subscript>2</Subscript> ceramics synthesized by a urea chemical-combustion method

Pure rutile phase of nanocrystalline (In?+?Nb) co-doped TiO₂ (INTO) ceramics were prepared by a chemical combustion method using urea as fuel. Dense ceramic microstructure can be obtained by sintering INTO nanocrystalline powders. Good dispersion of In³⁺ and Nb⁵⁺ co-doping ions in the microstructure is observed. Notably, high dielectric permittivity (≈20,674) and low loss tangent (≈0.054) at a low frequency and 30?°C are achieved in the (In_1/2Nb_1/2)_0.015Ti_0.985O₂ ceramic. Using an impedance spectroscopy, the INTO ceramics are confirmed to be electrically heterogeneous, consisting of semiconducting and insulating phases. The giant dielectric response in INTO ceramics can suitably be explained by the interfacial polarization. The low value of the loss tangent of INTO ceramics is attributed to a large value of resistivity of insulating phase.     

Dielectric properties of BaBi2Nb2O9 ceramics

The crystal structure and dielectric properties as a function of temperature for Ba-based with Bi-layered structure BaBi₂Nb₂O₉ (BBN) ceramics were investigated. The obtained results confirmed the relaxor ferroelectric behavior of the studied ceramics, including a strong frequency dispersion of the permittivity maximum and a visible shift of its temperature with frequency. Analysis of the real and imaginary part of permittivity allowed us to determine the values of Burn’s temperature and of the freezing temperature characterizing the relaxor ferroelectrics. The physical processes, responsible for the relaxor behavior of the studied ceramics are discussed. The additional low frequency dielectric dispersion at high temperatures in the paraelectric phase range was also observed. Correlation between this dispersion and the thermally stimulated depolarization current was ascertained.     

The effect of titanium compounds addition on the microwave dielectric properties of the ZnO–Nb2O5 ceramics for LTCC

The ZnO–Nb₂O₅ ceramics with titanium compounds were prepared by solid state reaction method. The effect of titanium compounds addition on the densification, phase development, microstructure and microwave dielectric properties of the ZnO–Nb₂O₅ ceramics was investigated. Adding TiO₂ to the ZnO–Nb₂O₅ ceramics in different order, the X-ray diffraction patterns showed that ZnTiNb₂O₈ was the main crystalline phase, only the minor crystalline phases were different. The TiO₂ phase could not coexist with ZnNb₂O₆ phase, but the CaTiO₃ phase could coexist with ZnNb₂O₆ phase. The effect of adding TiO₂ in different order on the microstructures of ZnO–Nb₂O₅ ceramics is unconspicuous. Compared to the ZnNb₂O₆–0.2CaTiO₃ ceramics, it is easier to lower the sintering temperature of the ZnNb₂O₆–1.8TiO₂ ceramics by doping BaCu(B₂O₅). The τ _f values of the ZnNb₂O₆–1.8TiO₂ ceramics and ZnNb₂O₆–0.2CaTiO₃ ceramics can be adjusted to zero by doping opposite τ _f values compounds, but the two mechanisms of adjusting τ _f are different.     

Low-temperature fabrication of BaBi2Nb2O9 ceramics by reaction controlled sintering

Reaction controlled sintering was applied to the fabrication of BaBi₂Nb₂O₉ (BBN) ceramics at lower temperature. A powder mixture of BaCO₃ and Nb₂O₅ was heated at 600 °C in a 1st step calcination to produce a binary precursor of BaNb₂O₆. The pre-heated powder was then mixed with a fixed amount of Bi₂O₃, which was subsequently pressed into a disk pellet. After a powder compact of the mixture was subjected to heating at 950 °C for 4 h, a BBN bulk sample with a relative density of 92% was successfully obtained. The low-temperature fabrication of dense BBN ceramics could be attributed to the inhibited formation of an intermediate phase of Ba₅ Nb₄O₁₅ and the production of submicron powder with an appropriate reactivity during a 1st step calcination.     

Influence of Nb2O5 doped amount on the property of BCTZ lead-free piezoelectric ceramics doped with Li2CO3

Ba_0.85Ca_0.15Ti_0.9Zr_0.1O₃ (BCTZ) lead-free piezoelectric ceramics doped with Nb₂O₅ (0.1, 0.3, 0.5, 0.7, 0.9 wt%) and Li₂CO₃ (0.6 wt%) were prepared by conventional solid-state reaction method. Influence of Nb₂O₅ doping amount on the piezoelectric property, dielectric property, phase composition and microstructure of prepared BCTZ lead-free piezoelectric ceramics doped with Li₂CO₃ were investigated by X-ray diffraction and scanning electron microscopy and other analytical methods. The results showed that the sintered temperature decreased greatly when the BCTZ lead-free piezoelectric ceramics were co-doped with Nb₂O₅ and Li₂CO₃; a pure perovskite structure of BCTZ lead-free piezoelectric ceramics co-doped with Nb₂O₅ and Li₂CO₃ sintered at 1,020 °C could be also obtained. The grain size decreased when Nb₂O₅ doping amount increased. The piezoelectric constant (d₃₃), the planar electromechanical coupling factor (k_p), the relative dielectric constant (ε_r) of BCTZ ceramics doped with Li₂CO₃ increased firstly and then decreased, the dielectric loss (tanδ) decreased firstly and then increased when Nb₂O₅ doping amount increased, indicating that Nb₂O₅ was “soft” additive. When Nb₂O₅ doping amount (z) was 0.7 wt% and Li₂CO₃ doping amount was 0.6 wt%, the BCTZ ceramics sintered at 1,020 °C possessed the best piezoelectric property and dielectric property, which d₃₃ was 238 pC/N, k_p was 29.33 %, ε_r was 4,691, tanδ was 2.07 %.     

Sintering behaviors and microwave dielectric properties of Ti-modified Ba<Subscript>3</Subscript>Ti<Subscript>5</Subscript>Nb<Subscript>6</Subscript>O<Subscript>28</Subscript> ceramics with 35BaO–35ZnO–30B<Subscript>2</Subscript>O<Subscript>3</Subscript> addition

Effect of 35BaO–35ZnO–30B₂O₃ (BZB) addition on the sintering behaviors, phase evolution and microwave dielectric properties of Ti-modified Ba₃Ti₅Nb₆O₂₈ (Ba₃Ti_5.1Nb_5.9O_27.95, BTNO) ceramics had been investigated. BZB addition effectively reduced the sintering temperature of BTNO from 1250 °C to about 900 °C. With increasing BZB addition, the crystal phase of the present ceramics changed from single phase Ba₃Ti₅Nb₆O₂₈ to mixing phases of Ba₃Ti₅Nb₆O₂₈ and Ba₃Ti₄Nb₄O₂₁. And the major phase gradually became from Ba₃Ti₅Nb₆O₂₈ to Ba₃Ti₄Nb₄O₂₁. Dielectric constant and temperature coefficient increased with the rising of BZB addition. But the Qf value gradually declined from 28000 to about 6000 GHz. The BTNO ceramics with 15% BZB addition exhibited excellent microwave dielectric properties as following: ε?=?46.3, Qf?=?5887 GHz and τ_f?=?35.5 ppm/°C, which was potential of candidate materials for LTCC application. And the variation of microwave dielectric properties had been also discussed with the phase and microstructure evolution.     

Electrical properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics modified with WO3

Ferroelectrics 0.67Pb (Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (PMN-PT) + x mol% WO₃ (x=0.1, 0.5, 1, 2) were prepared by columbite precursor method. Electrical properties of WO₃-modified ferroelectrics were investigated. X-ray diffraction (XRD) was used to identify crystal structure, and pyrochlore phase were observed in 0.67Pb (Mg_1/3Nb_2/3)O₃-0.33PbTiO₃+2 mol% WO₃. Dielectric peak temperature decreased with WO₃ doping, indicating that W⁶⁺ incorporated into PMN-PT lattice. Lattice constant, pyrochlore phase and grain size contribute to the variation of K_max. Both piezoelectric constant (d₃₃) and electromechanical coupling factors (k_p) were enhanced by doping 0.1 mol% WO₃, which results from the introduction of “soft” characteristics into PMN-PT, while further WO₃ addition was detrimental. We consider that the two factors, introduction of “soft” characteristics and the formation of pyrochlore phase, appear to act together to cause the variation of piezoelectric properties of 0.67PMN-0.33PT ceramics doping with WO₃.     

(5 − x)BaO-xMgO-2Nb2O5 ceramics prepared using a reaction-sintering process

(5 − x)BaO-xMgO-2Nb₂O₅ (x = 0.5 and 1; 5MBN and 10MBN) microwave ceramics prepared using a reaction-sintering process were investigated. Without any calcinations involved, the mixture of BaCO₃, MgO, and Nb₂O₅ was pressed and sintered directly. MBN ceramics were produced after 2-6 h of sintering at 1350-1500 °C. The formation of (BaMg)₅Nb₄O₁₅ was a major phase in producing 5MBN ceramics, and the formation of Ba(Mg_1/3Nb_2/3)O₃ was a major phase in producing 10MBN ceramics. As CuO (1 wt%) was added, the sintering temperature dropped by more than 150 °C. We produced 5MBN ceramics with these dielectric properties: ?_r = 36.69, Qf = 20,097 GHz, and τ_f = 61.1 ppm/°C, and 10MBN ceramics with these dielectric properties: ?_r = 39.2, Qf = 43,878 GHz, and τ_f = 37.6 ppm/°C. The reaction-sintering process is a simple and effective method for producing (5 − x)BaO-xMgO-2Nb₂O₅ ceramics for applications in microwave dielectric resonators.     

Fabrication and properties of PYN-PMN-PZT quaternary piezoelectric ceramics for high-power, high-temperature applications

xPb(Yb_1/2Nb_1/2)O₃ - 0.05Pb(Mn_1/3Nb_2/3)O₃ - (0.95 - x)Pb(Zr_0.48Ti_0.52)O₃ (PYN-PMN-PZT) quaternary piezoelectric ceramics were prepared by a traditional ceramics process. The effects of Pb(Yb_1/2Nb_1/2)O₃ (PYN) content on the phase structure, electrical properties and Curie temperature of the quaternary system were investigated in detail. The phase structure of PYN-PMN-PZT ceramics changed from tetragonal to rhombohedral with increasing PYN content. The piezoelectric coefficient (d₃₃), the electromechanical coupling factor (K_p) and the dielectric constant (ε₃₃^T/ε₀) reach maximum values near the morphotropic phase boundary (MPB), whereas the mechanical quality factor (Q_m) decreases. The sintered PYN-PMN-PZT ceramics exhibit high T_C, and as the PYN content increases, T_C decreases slightly. The MPB of the tetragonal and rhombohedral phase coexist and are located at a PYN composition of 0.12 ≤ x ≤ 0.14.The composition of PYN-PMN-PZT around the MPB showed high d₃₃ (> 300pC/N), K_p (> 0.50), Q_m (> 1000) and T_C (> 350 °C), meaning it is a very promising piezoelectric material for high-power and high-temperature applications.     

Comparative investigation of structure and dielectric properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 (65/35) and 10% PbZrO3-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (65/35) ceramics prepared by a modified precursor method

Relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (65/35) and 10% PbZrO₃-doped Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (65/35) ceramics were both prepared by a modified precursor method, which was based on the high-temperature synthesis of an oxide precursor that contained all the B-site cations for the consideration of B-site homogeneity. The dielectric properties of Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (65/35) ceramic was more of normal ferroelectric behavior, but the high dielectric constant (?_m = 34,200 at 1 kHz) and piezoelectric constant (d₃₃ = 709 pC/N) were observed for this composition close to the morphotropic phase boundary. Comparatively, introduction of 10% PbZrO₃ into Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (65/35) ceramics enhanced the diffuse phase transition as well as the rhombohedral to tetragonal phase transition temperature, while it also kept the high dielectric constant (?_m = 29,600 at 1 kHz) and piezoelectric constant (d₃₃ = 511 pC/N).     

Low temperature sintering and dielectric properties of Ba2Ti3Nb4O18 ceramics for silver co-sintering application

Low temperature sintering and dielectric properties of Ba₂Ti₃Nb₄O₁₈ ceramics with ZnO–B₂O₃–SiO₂ (ZBS) frit and lithium salts addition were investigated for silver co-sintering application. The sintering temperature of dense Ba₂Ti₃Nb₄O₁₈ ceramics with ZBS frit or LiNO₃ addition was effectively lowered to 950 or 1,000 °C, respectively. LiNO₃ is found to be more efficient than LiF or Li₂CO₃ to lower the sintering temperature of Ba₂Ti₃Nb₄O₁₈ ceramics. The sintering temperature of 900 °C was obtained for the Ba₂Ti₃Nb₄O₁₈ ceramics with a combination of ZBS frit and LiNO₃ addition. The dielectric properties of Ba₂Ti₃Nb₄O₁₈ ceramics with 1 wt.% ZBS and 0.5 wt.% LiNO₃ sintered at 900 °C are as follows: ε_r ~ 37.8, tan δ ~ 0.0003, τ_ε ~ 4.6 ppm/°C.     

Microstructure,dielectric, and energy storage performance of (Zn1/3Nb2/3)4+ complex-ion modified (Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 ceramics

In this study, (Ba_0.85Ca_0.15)(Zr_0.10Ti_0.90)_1-x(Zn_1/3Nb_2/3)_xO₃ ceramics were synthesized by conventional solid-phase methods, referred to as BCZT-xZN (x?=?0.0, 0.1, 0.2, 0.3, 0.4). The effects of adding different contents of (Zn_1/3Nb_2/3)⁴⁺ ion on the microstructure, dielectric and ferroelectric properties of BCZT ceramics were studied. Scanning electron microscopy (SEM) results showed that the average particle size of the samples was significantly reduced after the addition of (Zn_1/3Nb_2/3)⁴⁺ ion, and a second phase appeared when the addition amount was?≥?0.3. The dielectric properties show that with (Zn_1/3Nb_2/3)⁴⁺ ion replacing the B-site of BCZT ceramics, the dielectric constant decreases significantly and the Curie temperature decreases below room temperature. At the same time, we observed that the ceramic has good stability to temperature (-150 °C–200 °C) and frequency (10²–10⁶ Hz) changes. The addition of (Zn_1/3Nb_2/3)⁴⁺ ion can significantly reduce the residual polarization and improve the breakdown strength of ceramics. When x?=?0.3, The maximum energy storage density of ceramics is 0.994 J/cm³, which is about four times higher than that of pure BCZT ceramic (0.25 J/cm³). These findings fully demonstrate the great potential of BCZT ceramics in energy storage.

     

The phase transitions and dielectric properties of low temperature sintered ZnNb2O6–Zn3Nb2O8–TiTe3O8 microwave ceramics

ZnNb₂O₆–Zn₃Nb₂O₈–TiTe₃O₈ ceramics were fabricated by conventional ceramic processing. The effects of TiTe₃O₈ on the microstructures and dielectric properties of 0.7ZnNb₂O₆–0.3Zn₃Nb₂O₈ ceramics were investigated and the chemical reaction mechanisms of the phase transition were discussed. The results show that addition of TiTe₃O₈ will reduce the sintering temperature of ceramics. It is observed that ZnTiO₃, Zn₂TiO₄ and ZnTeO₃ phases coexist with ZnNb₂O₆ and Zn₃Nb₂O₈ phases, which results from the decomposition and reaction between Zn₃Nb₂O₈ and TiTe₃O₈. The morphology of ceramics changes significantly with increasing amounts of TiTe₃O₈. With increasing amount of TiTe₃O₈, the dielectric constant and the temperature coefficient of resonant frequency increase, while the Q × f value decreases. The optimized composition is 0.6(0.7ZnNb₂O₆–0.3Zn₃Nb₂O₈)–0.4TiTe₃O₈, which can be sintered at 670 °C and shows the best microwave dielectric properties with τ_f of 3 ppm/°C.