Development of perovskite in Fe-substituted Pb(Zn1/3Ta2/3)O3 and dielectric characteristics

Pb(Zn_1/3Ta_2/3)O₃ ceramics, compositionally modified by the incorporation of Fe to the octahedral lattice sites, were prepared and characterized in terms of perovskite development, dielectric properties, as well as microstructure evolution. The powders of the B-site precursor compositions were synthesized separately and reacted with PbO to form Pb[(Zn_1/3Ta_2/3),(Fe_1/2Ta_1/2)]O₃. The perovskite contents increased continuously with the Fe concentration. The maximum dielectric constant values of the ceramics increased tremendously with the fraction of Fe, whereas the dielectric maximum temperatures were rather insensitive to the compositional change.     

Preparation of Mg-modified Pb[Zn1/3(Ta0.4Nb0.6)2/3]O3 ceramics and dielectric characteristics

Mg (full composition range) and Nb (60 at %) were simultaneously substituted into Pb(Zn_1/3Ta_2/3)O₃, in an attempt to stabilize the perovskite structure. System powders were prepared using a B-site precursor method in order to enhance perovskite formation. The developed structures were examined by X-ray diffraction, from which perovskite phase yields as well as lattice parameters of the pyrochlore and perovskite were determined. Low-frequency dielectric responses of the ceramics were investigated. Phase transition modes (reflected in the dielectric constant spectra) were further analyzed in terms of diffuseness parameters.     

Perovskite phase developments in Pb[(Mg,Zn)1/3Ta2/3]O3 system and dielectric characteristics

Stabilization of a perovskite structure was attempted by replacing Mg for Zn in Pb(Zn_1/3Ta_2/3)O₃. System powders were prepared using a B-site precursor method by reacting PbO with separately-prepared precursor compositions. Effects of the substituent Mg concentration on perovskite phase developments and subsequent changes in dielectric properties were investigated, as a function of measurement frequency. Phase transition modes reflected in the dielectric constant spectra were analyzed in terms of diffuseness exponent and degree of diffuseness. Internal microstructures of the ceramics were examined, and correlations with perovskite phase contents and dielectric properties are discussed.     

Perovskite phase stabilization and dielectric properties of Pb(Zn1/3Ta2/3)O3–BaTiO3 ceramics

The phase structure and dielectric properties of (1 − x)Pb(Zn_1/3Ta_2/3)O₃–xBaTiO₃ (x = 0.00–0.40) ceramics were investigated. Pure perovskite is obtained when x ≥ 0.24. With increasing BT content, the diffuse phase transition and frequency dissipation of the dielectric constant increase and the dielectric maxima temperature decreases. It is related to the existing of Ba(Zn_1/3Ta_2/3)O₃ paraelectric microregions and the incomplete solid solution reaction between Pb(Zn_1/3Ta_2/3)O₃ and BaTiO₃.     

Dielectric responses in Mg<Subscript>1/3</Subscript>Ta<Subscript>2/3</Subscript>-replaced Pb[(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>),Ti]O<Subscript>3</Subscript> ceramics

Octahedral lattice sites of Pb[(Zn_1/3Nb_2/3),Ti]O₃ were replaced by 20 at.% Mg_1/3Ta_2/3 complex to enhance perovskite development, especially at Pb(Zn_1/3Nb_2/3)O₃-rich compositions. Resultant changes in the perovskite formation and associated dielectric responses were investigated. A perovskite structure was identified at Pb(Zn_1/3Nb_2/3)O₃-rich compositions by X-ray diffraction, although the development was rather incomplete. Phase transition modes in the dielectric constant spectra changed from diffuse to sharp ones, regardless of the introduction of Mg_1/3Ta_2/3. Dielectric maximum temperatures of the ceramics shifted linearly with the compositional change.     

Crystallographic and dielectric properties of barium-substituted Pb(Mg1/3Ta2/3)O3 ceramics

Ceramic powders of (Ba,Pb)Pb(Mg_1/3Ta_2/3)O₃ were prepared via a B-site precursor route. Crystal symmetries and lattice parameters were determined. Monophasic perovskite was developed after the two-step reaction process, in which the lattice parameters showed linear changes in the entire composition range. Dielectric responses of the ceramics with compositional and frequency changes were investigated. The results were also compared with the (Ba,Pb)(Zn_1/3Ta_2/3)O₃ data.     

Phase developments in the Pb(Zn1/2W1/2)O3-Pb(Zn1/3Ta2/3)O3-Pb(Zn1/3Nb2/3)O3 pseudo-ternary system

The phase stability ranges in the B-site precursor (Zn_1/2W_1/2)O₂-(Zn_1/3Ta_2/3)O₂-(Zn_1/3Nb_2/3)O₂ were determined by X-ray diffraction (XRD), where wolframite, tri-αPbO₂, and columbite phases were identified. Next attempts were carried out (with the addition of PbO) for the system Pb(Zn_1/2W_1/2)O₃-Pb(Zn_1/3Ta_2/3)O₃-Pb(Zn_1/3Nb_2/3)O₃, where the perovskite phase did not develop in the entire compositions investigated. Instead, only the Pb₂WO₅ and pyrochlore phases (along with ZnO) resulted.     

Dielectric characteristics of Mg-replaced Pb[(Zn1/3Ta2/3)0.2(Zn1/3Nb2/3)0.6Ti0.2]O3 ceramics

Powders of a Pb[(Zn_1/3Ta_2/3)_0.2(Zn_1/3Nb_2/3)_0.6Ti_0.2]O₃ system with gradual replacement of Zn by Mg were prepared by employing a B-site precursor method and developed structures were studied by X-ray diffractometry. Dielectric properties of the sintered ceramics were characterized under weak-field low-frequency conditions. A high maximum dielectric constant value of 38,000 (@1 kHz) was realized when 3/4 of octahedral Zn was replaced by Mg. Field-dependent polarization responses were also monitored at various temperatures to investigate ferroelectricity. Microstructures of the fractured ceramics were examined using a scanning electron microscope.     

The B-site order-disorder transformation in Pb(Sc1/2Ta1/2)O3 triggered by mechanical activation

Having pioneered mechanical activation on Pb-based relaxor ferroelectrics, we describe a unique order-disorder transformation phenomenon brought about by mechanical activation in Pb-based relaxor ferroelectrics of complex perovskite. B-site disorder in Pb(Sc_1/2Ta_1/2)O₃ (PST) which is traditionally tailored by thermal annealing after sintering at elevated temperatures, can be triggered by mechanical activation. The B-site disorder in Pb(Sc_1/2Ta_1/2)O₃ triggered by mechanical activation can well be retained in sintered Pb(Sc_1/2Ta_1/2)O₃, leading to an unique ferroelectric transition behavior (e.g., from a normal ferroelectric to relaxor) and a shift in the Curie temperature.     

Crystallographic and dielectric aspects of Pb[(Mg,Zn)1/3Ta2/3]O3 system with 40 at.% Nb substitution

A total of 40 at.% Nb was substituted for Ta in the Pb[(Mg,Zn)_1/3Ta_2/3]O₃ system in order to enhance perovskite development. System powders were prepared by a B-site precursor method. Perovskite formation yields and lattice parameters of the pyrochlore/perovskite structures were determined from X-ray diffraction results. Weak-field low-frequency dielectric responses of the system ceramics were investigated as functions of temperature, composition, and frequency. Phase transition modes reflected in the dielectric constant spectra were further analyzed in terms of diffuseness parameters.     

Preparation of stabilized Pb(Zn1/3Nb2/3)O3(PZN) films by the sol-gel method

Pb(Zn_1/3Nb_2/3)O₃ thick films with the perovskite structure were prepared by the sol-gel method. Niobium ethoxide Nb(OC₂H₅)₄, lead acetate Pb(CH₃COO)₂, and Zinc 2-ethylhexanoate Zn(O₂C₈H₁₅)₂ were reacted in 2-methoxyethanol to form the precursor. Titanium isopropoxide, Ti(O·i-C₃H₇)₄ and barium isopropoxide Ba(O·i-C₃H₇)₄ were added into the precursor solution to stabilize the formation of the perovskite phase. Films of upto 10 m thickness were obtained by controlling the viscosity of the solution and the dipping speed of silicon wafers. The phase evolution was investigated using differential thermal analysis (DTA) and X-ray diffraction techniques. The thickness-dependent dielectric constant of the resultant films is also reported.     

Dielectric properties of Pb(Zn<Subscript>1/3</Subscript>Ta<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-introduced (Ba,Pb)TiO<Subscript>3</Subscript> ceramic system

Ceramic powders of the Pb(Zn_1/3Ta_2/3)O₃-introduced BaTiO₃–PbTiO₃ system were prepared using a B-site precursor method. Perovskite formation tendencies of the system compositions were determined by X-ray diffraction. Weak-field low-frequency dielectric properties of the sintered ceramics were investigated. Dielectric constant spectra were further analyzed in terms of diffuseness. Internal microstructures of the ceramics were also examined.     

Microwave dielectric properties of mixed phase ceramics, Ba(Zn1/3Ta2/3)O3–xCaTiO3 and xMgTiO3–yCaTiO3–z(Nd2O3,wTiO2)

The effect of different chemical compositions on the microwave dielectric properties of Ba(Zn_1/3Ta_2/3)O₃–xCaTiO₃ and xMgTiO₃–yCaTiO₃–z(Nd₂O₃,wTiO₂) was studied. High fQ dielectrics were designed by optimizing composition and firing conditions. Adding up to 1 mol % CaTiO₃ to Ba(Zn_1/3Ta_2/3)O₃ increased ε_r from 25 to 30 at a firing temperature of 1450 °C, and produced very high fQ values of more than 100 000 GHz at a firing temperature of 1550 °C. EPMA and XRD suggested that ceramics based on Ba(Zn_1/3Ta_2/3)O₃ with CaTiO₃ had mixed phases of Ba(Zn_1/3Ta_2/3)O₃ and Ca–Ti–Zn–O. Addition of CaTiO₃ increased the Ba(Zn_1/3Ta_2/3)O₃ peak observed in XRD and decreased the Ba₃Ta₂O₈ peak. Prolonged sintering of Ba(Zn_1/3Ta_2/3)O₃ with CaTiO₃ increased the fQ value but kept ε_r constant. 0.5MgTiO₃–0.5CaTiO₃–z(Nd₂O₃,wTiO₂) showed a high dielectric constant ε_r>40 and fQ>20 000 GHz. When w=1, τ_f decreased linearly with z around 0 ppm/ °C in 0.5MgTiO₃–0.5CaTiO₃–z(Nd₂O₃,TiO₂) (0.25≤z≤0.5). X-ray and EDX analysis revealed a mixed phase matrix of MgTiO₃ and (Ca_1?αNd_2α/3)Ti_βO₃. It was concluded that ε_r of the high fQ materials Ba(Zn_1/3Ta_2/3)O₃–xCaTiO₃ and xMgTiO₃–yCaTiO₃–z(Nd₂O₃,wTiO₂) would be increased by varying their chemical compositions, x, y, z, and w, and that their fQ value would be improved by appropriate choices of heating temperature and time.     

Dielectric properties of Pb[(1?x)(Zr1/2Ti1/2)?x(Zn1/3Ta2/3)]O3 ceramics prepared by columbite and wolframite methods

Polycrystalline samples of Pb[(1 − x)(Zr_1/2Ti_1/2) − x(Zn_1/3Ta_2/3)]O ₃ , where x = 0.1–0.5 were prepared by the columbite and wolframite methods. The crystal structure, microstructure, and dielectric properties of the sintered ceramics were investigated as a function of composition via X-ray diffraction (XRD), scanning electron microscopy (SEM), and dielectric spectroscopy. The results indicated that the presence of Pb(Zn_1/3Ta_2/3)O₃ (PZnTa) in the solid solution decreased the structural stability of overall perovskite phase. A transition from tetragonal to pseudo-cubic symmetry was observed as the PZnTa content increased and a co-existence of tetragonal and pseudo-cubic phases was observed at a composition close to x = 0.1. Examination of the dielectric spectra indicated that PZT–PZnTa exhibited an extremely high relative permittivity at the MPB composition. The permittivity showed a ferroelectric to paraelectric phase transition at 330 °C with a maximum value of 19,600 at 100 Hz at the MPB composition.     

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 Pb(Zn1 / 2W1 / 2)O3 introduction on perovskite development and dielectric properties of (Ba,Pb)TiO3

Powders of a Pb(Zn_1 / 2W_1 / 2)O₃-introduced BaTiO₃-PbTiO₃ system were prepared. A two-step calcination route of a B-site precursor method was employed to promote perovskite formation. The overall effects of the Pb(Zn_1 / 2W_1 / 2)O₃ incorporation on changes in crystalline aspects as well as dielectric properties were explored.     

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.     

Processing, sintering characteristics and dielectric properties of barium-substituted Pb(Mg1/3Nb2/3)O3–PbTiO3 solid solution

Solid solutions in the lead-based relaxor system Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ were modified by minor substitutions of Ba in the Pb-site of the perovskite lattice. The modified compositions were calcined at 830 °C for 3 h to yield fine-grained, single-phase perovskite materials. A small amount of excess MgO(0.05 wt %), which mostly served as a sintering aid, was added to the calcined batches and the resulting mixtures were sintered at temperatures between 1150 and 1250 °C for periods ranging from 3 to 5 h. The substitutions of BaO for PbO in the perovskite solid solution lattice caused a progressive lowering of the Curie point with increasing BaO content. On average, the Curie point decreased by about 10 °C for each mole of BaO substituted for PbO. Among the various Ba-substituted solid solutions studied, the one with a nominal composition Pb_0.99Ba_0.01[(Mg_1/3Nb_2/3)_0.9Ti_0.1]O₃ which has a Curie point located near 28 °C, exhibited excellent dielectric properties. On sintering at 1250 °C for 3 h, this composition yielded a density near 96% of the theoretical density. The peak dielectric constant of the composition at 1 KHz was slightly higher than 22000, and the corresponding tan δ value was 1.5% with a specific resistivity of 2.5 × 10¹² Ω cm^-1. This revised version was published online in November 2006 with corrections to the Cover Date.     

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.     

Synthesis of perovskite Pb(Zn1/3Nb2/3)O3 powders via a polymer complex solution route with a large excess of polyethylene glycol

A polymer complex solution process was employed to produce perovskite Pb(Zn_1/3Nb_2/3)O₃ (PZN) from a solution comprising Pb(NO₃)₂, ZnCl₂, NbCl₅ and polyethylene glycol (PEG). X-ray diffraction peaks due to the perovskite phase were observed after firing at temperatures between 700 and 1000°C. By increasing the concentration of PEG, the perovskite phase appeared at a lower temperature. With 600 vol% PEG and after heating at 800°C for 1 h, perovskite PZN amounted to 91 % of the total solid product. The role of ligand-to-metal charge transfer during polymer complex formation on the apparent stabilization of PZN is discussed by using UV-VIS.