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.     

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.     

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.     

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.     

Effect of excess PbO and sintering temperature on the templated grain growth of Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)<Subscript>0.67</Subscript>Ti<Subscript>0.33</Subscript>O<Subscript>3</Subscript> polycrystals

The effect of excess lead oxide and sintering temperature on the microstructure evolution in the templated grain growth (TGG) of the Pb(Mg_1/3Nb_{2/ 3})_0.67Ti_0.33O₃ (PMNT67/33) polycrystals was investigated. By adding excess PbO in the precursor of PMNT ceramics, the textured structure of PMNT polycrystals was obtained near SrTiO₃ (ST) template by the conventional ceramic technique. The texture profiles developed progressively with increasing the concentration of excess PbO. A suitable sintering temperature is also very essential to grow a thick textured layer and avoid a second phase. Furthermore, the through-thickness of the PMNT textured layer is strongly influenced by the uniaxial compact-pressure of preparing the ST seeded PMNT specimen.     

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.     

Effect of La substitution on structural and electrical properties of Ba(Fe<Subscript>2/3</Subscript>W<Subscript>1/3</Subscript>)O<Subscript>3</Subscript> nanoceramics

The nanocrystalline fine powders (∼80 nm) of (Ba_1−x La _x )(Fe_2/3W_1/3)_1−x/4O₃, (BLFW) (x = 0.0, 0.05, 0.10 and 0.15) were synthesized with a combined mechanical activation and conventional high-temperature solid-state reaction methods. Preliminary X-ray structural analysis of pellet samples (prepared from fine powders) showed formation of a single-phase tetragonal system. Detailed studies of dielectric properties (ε_r and tan δ) exhibit that these parameters are strongly dependent on frequency, temperature and La composition. The La-substitution increases the dielectric constant and decreases the tan δ up to 10% substitutions of La at the Ba-site, and then reversed the variation, and hence this composition is considered as a critical composition. This observation was found valid for structure, microstructures, dielectric constant, electrical conductivity, J–E characteristics and impedance parameters also. Like in other perovskites (PZT, BZT), La substitution plays an important role in tailoring the properties of Ba(Fe_2/3W_1/3)O₃ ceramics.     

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.     

Strain-induced artificial multiferroicity in Pb(Zr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript>/Pb(Fe<Subscript>0.66</Subscript>W<Subscript>0.33</Subscript>)O<Subscript>3</Subscript> layered nanostructure at ambient temperature

Layered nanostructures (LNs) of the commercial ferroelectric Pb(Zr_0.53Ti_0.47)O₃ (PZT) and the natural ferroic relaxor Pb(Fe_0.66W_0.33)O₃ (PFW) were fabricated with a periodicity of PZT/PFW/PZT (~5/1/5 nm, thickness ~250 nm) on MgO substrates by pulsed laser deposition. The dielectric behavior of these LNs were investigated over a wide range of temperatures and frequencies, observing Debye-type relaxation with marked deviation at elevated temperatures (>400 K). High dielectric constant and very low dielectric loss were observed below 100 kHz and 400 K, whereas the dielectric constant decreases and loss increases with increase in frequency, similar to relaxor ferroelectrics. Asymmetric ferroelectric hysteresis loops across UP and DOWN electric field were observed with high remanent polarization (P_r) of about 33 μC/cm². High imprint (~5–7 V across 250 nm thin films) were seen in ferroelectric hysteresis that may be due to charge accumulation at the interface of layers or significant amount of strain (~3.21) across the layers. Room temperature ferromagnetic hysteresis was observed with remanent magnetization 5.32 emu/cc and a coercive field of ~550 Oe. Temperature and field dependent leakage current densities showed very low leakage ~10⁻⁷–10⁻⁵ A/cm² over 500 kV/cm. We observed imprint in hysteresis that may be due to charge accumulation at the interface of layers or active role of polar nano regions (PNRs) situated in the PFW regions.     

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.     

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.     

Preparation of magnetic composites through SrO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass crystallization

Glasses with nominal compositions 11SrO · 5.5Fe₂O₃ · 4.5Al₂O₃ · 4B₂O₃ (1) and 15SrO · 5.5Fe₂O₃ · 4.5Al₂O₃ · 4B₂O₃ (2) were prepared by rapidly quenching oxide melts between counterrotating steel rollers. The glasses were then heat-treated in the range 650–950°C to produce glass-ceramic samples. The samples were characterized by X-ray diffraction, electron microscopy, and magnetic measurements. The phase composition of the glass-ceramics was determined, and their microstructure and magnetic properties were studied. The annealing temperature was shown to have a strong effect on the coercivity of the materials, which reaches 650 and 570 kA/m for compositions 1 and 2, respectively.     

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.     

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.     

Structural,optical spectroscopy,optical conductivity and dielectric properties of BaTi<Subscript>0.5</Subscript>(Fe<Subscript>0.33</Subscript>W<Subscript>0.17</Subscript>)O<Subscript>3</Subscript> perovskite ceramic

Fe and W co-substituted BaTiO₃ perovskite ceramics, compositional formula BaTi_0.5(Fe_0.33W_0.17)O₃, were synthesized by the standard solid-state reaction method and studied by X-ray diffraction, scanning electron microscopy and spectroscopy ellipsometry. The prepared sample remains as double phases with the perovskite structure. The structure refinement of BaTi_0.5(Fe_0.33W_0.17)O ₃ sample was performed in the cubic double and hexagonal setting of the \(\text {Fm}\boldsymbol {\bar {{3}}\mathrm {m}}\) and P6 ₃ /mmc space groups. Spectral dependence of optical parameters; real and imaginary parts of the dielectric function, refractive index, extinction coefficient and absorption coefficient were carried out in the range between 1.4 and 4.96 eV by using the ellipsometry experiments. Direct bandgap energy of 4.36 eV was found from the analysis of absorption coefficient vs. photon energy. In addition, the oscillator energy, dispersion energy and zero-frequency refractive index values were found from the analysis of the experimental data using Wemple–DiDomenico single-effective-oscillator model.     

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 properties of B<Subscript>2</Subscript>O<Subscript>3</Subscript> doped Sm(Co<Subscript>1/2</Subscript>Ti<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> ceramics at microwave frequency

The microwave dielectric properties and the microstructures of Sm(Co_1/2Ti_1/2)O₃ ceramics with B₂O₃ additions (0.25 and 0.5 wt%) prepared by conventional solid-state route have been investigated. The prepared Sm(Co_1/2Ti_1/2)O₃ exhibited a mixture of Co and Ti showing 1:1 order in the B-site. Doping with B₂O₃ (up to 0.5 wt%) can effectively promote the densification of Sm(Co_1/2Ti_1/2)O₃ ceramics with low sintering temperature. It is found that Sm(Co_1/2Ti_1/2)O₃ ceramics can be sintered at 1,260 °C due to the grain boundary phase effect of B₂O₃ addition. At 1,290 °C, Sm(Co_1/2Ti_1/2)O₃ ceramics with 0.5 wt% B₂O₃ addition possess a dielectric constant (ε _r) of 27.7, a Q × f value of 33,600 (at 9 GHz) and a temperature coefficient of resonant frequency (τ_f) of −11.4 ppm/ °C. The B₂O₃-doped Sm(Co_1/2Ti_1/2)O₃ ceramics can find applications in microwave devices requiring low sintering temperature.     

Thermal Analysis of the Ternary System Li<Subscript>2</Subscript>WO<Subscript>4</Subscript>-WO<Subscript>3</Subscript>-Li<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript>

Thermal analysis results indicate that the liquidus surface of the Li₂WO₄-WO₃-Li₂B₄O₇ system consists of the primary phase fields of Li₂WO₄, Li₂B₄O₇, WO₃, Li₂WO₄ · WO₃ (congruent melting), 3Li₂WO₄ · 2Li₂B₄O₇ (congruent melting), and Li₂WO₄ · 3WO₃ (incongruent melting). Low-melting-point compositions are selected that are potentially attractive for the low-temperature synthesis of lithium tungsten bronze powders.     

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.