Phase developments in Pb(Mg<Subscript>1/2</Subscript>W<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> and Pb(Zn<Subscript>1/2</Subscript>W<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> via B-site precursor route

Phase formation stages of MgWO₄ and ZnWO₄ (precursor compositions for following steps) were investigated by monitoring the reactions of oxide chemicals at various temperatures. Developed phases were examined by using X-ray diffraction (XRD). Successive attempts were also conducted for Pb(Mg_1/2W_1/2)O₃ (PMW) and Pb(Zn_1/2W_1/2)O₃ (PZW) by reacting PbO with the precursor compounds. Stages of phase development in the two compositions were also analyzed. The results are compared with those of another tungsten-containing perovskite Pb(Fe_2/3W_1/3)O₃ (PFW) and its B-site precursor Fe₂WO₆. After PbO addition to the precursor powders, a perovskite phase formed directly (i.e., without any intermediate phases) in the case of PMW. For PbO + ½ZnWO₄, in contrast, the decomposition of ZnWO₄ and preferential reaction with PbO resulted in Pb₂WO₅ and ZnO, instead of the perovskite PZW.     

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.     

Perovskite formation and dielectric responses in Pb(Zn1/3Nb2/3)O3-modified Pb(Zn1/3Ta2/3)O3-PbTiO3 ceramics

Pb(Zn_1/3Ta_2/3)O₃-PbTiO₃ ceramic compositions were modified by the introduction of Nb to the octahedral lattice sites. Resultant tendencies in the perovskite formation and dielectric properties were examined. System powders were prepared using a B-site precursor method. Developed structures and lattice parameters of the system compositions were investigated by powder X-ray diffractometry, from which the parameter of a hypothetical perovskite Pb(Zn_1/3Ta_2/3)O₃ is proposed. Weak-field low-frequency dielectric responses of the system ceramics were measured.     

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.     

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.     

Dielectric characteristics of Pb(Zn<Subscript>1/3</Subscript>Ta<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-BaTiO<Subscript>3</Subscript> ceramics with/without PbTiO<Subscript>3</Subscript> modification

Stabilization tendencies of the perovskite structure in a Pb(Zn_1/3Ta_2/3)O₃-BaTiO₃ pseudobinary system with/without compositional modification by 20 mol% PbTiO₃ introduction were compared. In order to promote perovskite phase formation, the B-site precursor method (which is conceptually similar to the columbite process) was employed in this study. Dielectric properties of sintered samples were investigated as functions of composition and measurement frequency. Dielectric constant spectra, in the paraelectric temperature region, were further analyzed in terms of diffuseness. Microstructures of sintered specimens were also investigated and correlated with perovskite stabilization.     

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.     

Preparation and phase formation of perovskite Pb(Ni<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> by a reaction-sintering process

Pyrochlore-free Pb(Ni_1/3Nb_2/3)O₃ perovskite ceramics produced by a simple and effective reaction-sintering process were investigated. Without any calcination, the mixture of PbO, Ni(NO₃)₂ and Nb₂O₅ was pressed and sintered directly into PNN ceramics. Density of 98.5% of theoretical value was obtained after sintered at 1230 °C for 2 h in air. 99.3% of theoretical density was obtained after sintered at 1,200 °C for 2 h in PbO compensated atmosphere. PNN ceramic with dielectric constant 1,680 at 25 °C and 1 kHz has been obtained.     

Preparation of Pb(Zr,Ti)O<Subscript>3</Subscript>–Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> piezoelectric ceramics by dry–dry method

Ternary perovskite ceramics of Pb[(Zr_0.5Ti_0.5)_0.8−x (Mg_1/3Nb_2/3)_0.2+x]_0.98Nb_0.02O_3.01 (PZTMN, x = −0.075, −0.05, −0.025, 0, 0.025, 0.05, and 0.075 ), are synthesized via dry–dry method. B-site precursors of PZTMN ([(Zr_0.5Ti_0.5)_0.8−x (Mg_1/3Nb_2/3)_0.2+x ]_0.98Nb_0.02O_2.01, ZTMN) can be synthesized via a two-step solid state reaction method. The first calcination temperature is 1,300 °C, and the second is not higher than 1,360 °C. Incorporation of magnesium and niobium ions promotes the formation of the single phase solid solution with ZrTiO₄ structure. Single phase perovskite PZTMN is formed at 780 °C, much lower than that in conventional process. Dense ceramics can be sintered at about 1,260 °C with dielectric and piezoelectric properties comparable to that of wet–dry method and higher than that of conventional method. It seems that B-site precursor method is cost effective in preparation of ternary piezoelectric ceramics.     

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.     

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.     

Synthesis and characterization of pseudo-ternary Pb(Fe<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>)O<Subscript>3</Subscript>-PbZrO<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> ferroelectric ceramics via a B-site oxide mixing route

Perovskite phase formation and dielectric/ferroelectric properties of the pseudo-ternary Pb(Fe_1/2Nb_1/2)O₃-PbZrO₃-PbTiO₃ (PFN-PZ-PT) ferroelectric ceramics have been investigated as promising materials for multi-layer ceramic capacitors. Complete solid solution with pure perovskite phase can be formed in this system in the whole composition range studied using conventional solid-state reaction method via a B-site oxide mixing route. Crystal lattice of the ceramics obtained shrinkages with the increase of the concentration of Pb(Fe_1/2Nb_1/2)O₃ (PFN) and expands with the increase of the content of PbZrO₃ (PZ). With the increase of the concentration of PbTiO₃ (PT), crystal structure of PFN-PZ-PT changes from pseudo-cubic ferroelectric phase to tetragonal one while retains the fraction of PFN as constant. A morphotropic phase boundary (MPB) forms at the composition of 42 mol% PT regardless of whatever concentration of PFN, and the content of PFN affects little on the composition of MPB. The preliminary phase diagram of the PFN-PZ-PT system is determined by X-ray diffraction (XRD) measurements combining with dielectric/ferroelectric characterization. Dielectric measurements indicate that the value of dielectric maximum (ɛ_m) and the temperature where ɛ_m appears (T_m) increase with the increase of the concentration of PT. However, PFN exhibits opposite effects, i.e., ɛ_m increases with the increase of the concentration of PFN accompanied by the decrease of T_m.     

Structural and electrical properties of Ba(Sb<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> ceramic

Lead-free perovskite Ba(Sb_1/2Nb_1/2)O₃ was prepared by conventional ceramic fabrication technique at 1200 °C/5 h in air atmosphere. The crystal symmetry, space group and unit cell dimensions were determined from the experimental results using FullProf software whereas crystallite size and lattice strain were estimated from Williamson–Hall approach. XRD analysis of the compound indicated the formation of a single-phase monoclinic structure with the space group P2/m. EDAX and SEM studies were carried out to evaluate the quality and purity of the compound. Dielectric study revealed the frequency-dependent dielectric anomaly. To find a correlation between the response of the real system and idealized model circuit composed of discrete electrical components, the model fittings were presented using the impedance data. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in Ba(Sb_1/2Nb_1/2)O₃. The ac conductivity data were used to evaluate the density of states at Fermi level, minimum hopping length and apparent activation energy of the compound.     

Effect of substitution of titanium by magnesium and niobium on structure and piezoelectric properties in (Bi<Subscript>1/2</Subscript>Na<Subscript>1/2</Subscript>)TiO<Subscript>3</Subscript> ceramics

To develop new (Bi_1/2Na_1/2)TiO₃-based ceramics with excellent piezoelectric properties, the similarities and the differences between PZT and (Bi_1/2Na_1/2)TiO₃ ceramics were analysed. Based on the analysis, a new (Bi_1/2Na_1/2)TiO₃-based piezoelectric ceramic of B-site substitution of complex ions (Mg_1/3Nb_2/3)⁴⁺ for Ti⁴⁺ was prepared by a conventional ceramic technique, and effect of complex ions (Mg_1/3Nb_2/3)⁴⁺ addition on the microstructure, dielectric and piezoelectric properties was investigated. The results show that all compositions are mono-perovskite phase and the grain size increases with increasing content of (Mg_1/3Nb_2/3)⁴⁺. The piezoelectric constant, d ₃₃, first increases and then decreases, and electromechanical coupling factor, k _p, varies insignificantly with increasing content of (Mg_1/3Nb_2/3)⁴⁺.     

Effect of Bi substitution level on dielectric characteristics of Pb[(Mg1/3Nb2/3),Ti]O3 ceramics

Bi(Mg_2/3Nb_1/3)O₃ was systematically substituted (up to 30 mol%) into Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ and resultant changes in the phase formation, crystallographic aspects as well as dielectric properties of the ceramic samples were investigated. Columbite and rutile solid solutions were mostly detected in the B-site precursor compositions, whereas only a monophasic perovskite structure was identified after the addition of PbO and Bi₂O₃. Frequency-dependent dielectric relaxation behavior was observed in all of the compositions investigated. The maximum dielectric constant values decreased substantially with increasing substituent fractions of Bi. By contrast, the dielectric maximum temperatures changed in somewhat complicated ways in that the increase became comparatively insensitive to the PbTiO₃ concentration with increasing levels of Bi substitution.     

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.     

Preparation and electrical properties of Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> solid solutions

Ceramic samples of lead magnesium niobate (PMN) and (1 ? x)Pb(Mg_1/3Nb_2/3)O₃?xPbTiO₃ (PMN-PT) solid solutions with x = 0, 0.05, 0.10, and 0.30 have been prepared by solid-state reactions, and their structural, electrical, and piezoelectric properties have been studied using x-ray diffraction, Rietveld profile analysis, impedance spectroscopy, and the resonance/antiresonance method. The results indicate that the use of nonstoichiometric columbite niobates enables the synthesis of phase-pure PMN and PMN-PT.     

Dielectric and magnetic properties of Ca(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>/NiZn ferrite composites

Dense Ca(Zn_1/3Nb_2/3)O₃/NiZn ferrite composites with homogeneously fine microstructures were prepared through conventional solid-state method. The powder XRD patterns confirm the coexistence of the two phases. The dielectric properties in the low frequency range (100 Hz–1 MHz) follow the rule of Maxwell–Wagner interfacial polarization. The dielectric and magnetic properties in the high frequency range (10 MHz–1 GHz) are also reported. The results show that this kind of magnetic–dielectric composites could be used in high-frequency communications for the capacitor-inductor integrating devices such as electromagnetic interference filters and antennas.     

Solid-state reactions in the system Li<Subscript>2</Subscript>CO<Subscript>3</Subscript>-Na<Subscript>2</Subscript>CO<Subscript>3</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript>

The formation mechanisms of Li _x Na_{1 ?x} Ta _y Nb_{1 ? y} O₃ perovskite solid solutions in the Li₂CO₃-Na₂CO₃-Nb₂O₅-Ta₂O₅ system have been studied by x-ray diffraction, differential thermal analysis, thermogravimetry, IR spectroscopy, and mass spectrometry at temperatures from 300 to 1100°C. The results indicate that the synthesis of Li _x Na_{1 ? x} Ta _y Nb_{1 ? y} O₃ solid solutions involves a complex sequence of consecutive and parallel solid-state reactions. An optimized synthesis procedure for Li _x Na_{1 ? x} Ta _y Nb_{1 ? y} O₃ solid solutions is proposed.     

Fabrication of thin films by sputtering deposition using (Ba<Subscript>0.3</Subscript>Sr<Subscript>0.7</Subscript>)(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> ceramic as target

Dielectric ceramic thin films were fabricated on SiO₂ (110) substrates by the radio frequency (RF) magnetron sputtering method using (Ba_0.3Sr_0.7)(Zn_1/3Nb_2/3)O₃ microwave dielectric ceramic as target. The microstructure, components, and morphology of the thin films were investigated thoroughly. The results reveal that the experimental conditions can affect the growth of the thin films significantly. The main phases of the thin films are Ba_0.5Sr_0.5Nb₂O₆ and Ba_0.27Sr_0.75Nb₂O_5.78, which are of different composition from that of the ceramic target due to Zn loss. The thin films are polycrystalline with high-quality crystalline and are made up of dense rod-like structures. The growth mechanism of the thin films is discussed in particular.