Synthesis of (Pb,La) (Zr,Ti)O3 films using a diol based sol–gel route

Morphotropic phase boundary compositions of lead zirconate titanate (PZT) modified with 2, 5 and 10 mol% lanthanum (PLZT) have been prepared using a diol based sol–gel route. Thin films of these PLZT compositions were fabricated on platinized silicon substrates by a spin coating technique. The effects of firing temperature and lanthanum modifications were investigated with regard to phase development, microstructure, and ferroelectric and dielectric characteristics. A strong 1 1 1 orientation developed as the amount of lanthanum doping increased. The results indicate that the values of remanent polarization, P _r, and dielectric constant, _r, decrease, relative to unmodified PZT, for films modified with 2 and 5 mol% lanthanum. The 5 mol% La films for example had a P _r of 14 C cm^–2 and an _r value of 700 compared to 31 C cm^–2 and 1480 for undoped PZT films. At these La concentrations there was also an improvement in the leakage current density by two orders of magnitude compared with unmodified PZT. The 10 mol% La sample did not exhibit any switchable polarization behaviour.     

Thickness-dependent electrical properties of sol–gel derived Pb(Zr0.52Ti0.48)O3 thick films using PbTiO3 buffer layers

Pb(Zr_0.52Ti_0.48)O₃ (PZT) thick films, with thickness up to 4 μm, using PbTiO₃ (PT) buffer layers were successfully prepared on silicon-based substrates by a sol–gel method. Thermal analysis (thermogravimetric–differential thermal analysis) of PT and PZT sols were used to determine the pyrolysis and annealing temperatures. X-ray diffraction results show that the PZT/PT composite thick films possess perovskite structure and the dominant crystalline orientation changes from (100) to (110) with increasing the film thickness. Furthermore, the composite thick films exhibit thickness-dependent ferroelectric and dielectric properties, i.e., the coercive field decreases while dielectric constant increases as the thickness increases. Theoretical analysis shows that the thickness-dependent electrical properties are mainly attributed to the low dielectric constant of PT buffer layer and the relaxation of internal stress in PZT films.     

Oleic acid assisted synthesis of CaCu3Ti4O12 powders and ceramics by sol–gel process

The CaCu₃Ti₄O₁₂ (CCTO) powders were prepared via a sol–gel method using oleic acid (OA) as surfactant. The obtained samples were characterized by thermogravimetric/differential scanning calorimeter Fourier transform-infrared spectroscopy, X-ray diffraction (XRD) and scanning electron microscope, the relative density and the dielectric properties of the ceramics were also investigated. The XRD patterns confirm the formation of CCTO crystal phase and no new peaks appeared whether the dispersant was added or not. The dispersibility of the CCTO powders is improved by adding OA as surfactant. The CCTO prepared without surfactant contains particles of various sizes ranging from 200 to 250 nm whereas the CCTO prepared with OA shows uniform particle size about 120–150 nm. The CCTO ceramics prepared with OA has higher dielectric constant (199484) and lower dielectric loss (0.0977) at 25 °C (10 kHz).     

Synthesis, characterization, and sintering of sol–gel derived cordierite ceramics for high-frequency MLCIs

The synthesis, characterization, and sintering of sol–gel derived cordierite ceramics are investigated in the present paper. Synthesis was carried out by optimizing two main preparation parameters. The effect of the heat-treatment schedule on crystallization and the properties of crystalline phases were analyzed. The additives B₂O₃ and P₂O₅ were utilized to promote the crystallization or transformation to -cordierite and sintering. This material has a low dielectric constant and a low dissipation factor and can be co-fired with high conductivity metals such as Au, Ag/Pd, Cu paste at low temperature (below 1000 °C), suggesting that it would be a promising material for high-frequency MLCIs.     

Grain growth,densification and electrical properties of lead-free piezoelectric ceramics from nanocrystalline (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 powder by sol–gel technique

The sintering behavior revealed in the sintering processes of the conventional and a two-step process and electrical properties of the (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ ceramics from the nanocrystalline powders synthesized by a sol–gel technique were systematically studied. It was found that the sintering process of the (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ ceramics made from nanocrystalline powders was significantly improved, the sintering temperature was reduced markedly from 1,540 to 1,280 °C, as well as a high relative density (>97 %) was obtained in the conventional sintering. Under the two-step sintering conditions, the full densification and the most suppression of grain growth was achieved simultaneously. The (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ ceramics from nanocrystalline powders sintered by the two-step sintering technique (sintered at T ₁ of 1,300 °C for 1 min and T ₂ of 1,150 °C for 20 h) exhibited the optimum average grain size of 700 nm and a high relative density of 98 %. The electrical properties of the (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ ceramics were greatly influenced by the grain size and phase structure formed under the both sintering conditions, with sintering temperature and grain size increased, the electrical properties of the (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ ceramics, which made from nanocrystalline powders, shows an enhancing trend: d ₃₃ ~100 pC/N, k _p ~53.3 % for the specimen sintered at 1,300 °C for 1 min and 1,150 °C for 20 h, d ₃₃ ~310 pC/N, k _p ~53.3 % for the specimen sintered at 1,350 °C for 2 h respectively.     

Synthesis and characterization of sol–gel derived (Ba,Ca)(Ti,Zr)O<Subscript>3</Subscript> nanoparticles

A citrate precursor method was employed to synthesize lead-free perovskite 0.5Ba(Zr_0.2Ti_0.8)O₃-0.5(Ba_0.7Ca_0.3)TiO₃ (BZT-0.5BCT) crystallites. Powders and gels were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectra, thermal analysis and transmission electron microscopy. It was indicated that BZT-0.5BCT transparent gel can be obtained via the chelation of citric acid with metal ions. Gels transformed into crystalline powders with single-phase perovskite structure when heat-treated above 650 °C, significantly lower than that in a solid-state reaction method. The primary particle size of the powders increased from 30 to 60 nm as the decomposition temperature was raised from 600 to 750 °C.     

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.     

Synthesis and electrical properties of Pb(Zr0.52Ti0.48)O3 thick films embedded with ZnO nanoneedles prepared by the hybrid sol–gel method

Pb(Zr_0.52Ti_0.48)O₃ thick films embedded with ZnO nanoneedles (PZT–ZnO_n) were successfully prepared on Pt/Cr/SiO₂/Si substrates by the hybrid sol–gel method via spin-coating ZnO_n suspension and lead zirconate titanate (PZT) sol. To control the orientation of the films, a PbTiO₃ (PT) layer was first deposited as a seed layer. Effects of annealing method and ZnO_n contents on the corresponding orientation and crystallization of PZT–ZnO_n films were investigated by XRD and SEM. The results show that all the PZT–ZnO_n composite thick films have pure perovskite structure and high-quality film surface. The dielectric and ferroelectric properties of the PZT–ZnO_n films are close to the PZT films, and have a little decrease with the increasing of the ZnO_n contents.     

Physical and electrical properties of MnO2-doped Pb(Zr x Ti1−x )O3 ceramics

The effects of composition on the physical property change in the phase coexistence region between the tetragonal and rhombohedral phases have been investigated as a function of zirconium concentration, x, for the MnO₂-doped Pb(Zr _x Ti_1–x )O₃ (0.40x0.60) ceramics. The relative amount of phase coexisting between the tetragonal and rhombohedral phases affects greatly both dielectric and piezoelectric properties as a function of zirconium concentration. However, there are no detectable changes between the apparent density and microstructure. Also, in the coexistence region, the relative amount of coexistence of the rhombohedral phase increases with MnO₂ addition. The inflection points of the dielectric constant shift to lower zirconium concentration in proportion to the MnO₂ addition, owing to the substitution effect on the PZT lattice site.     

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.     

Density variation and piezoelectric properties of Ba(Ti1 − x Sn x )O3 ceramics prepared from nanocrystalline powders

Nanocrystalline powders of tin-doped barium titanate with different concentrations of tin have been synthesized by a combination of solid state reaction and high-energy ball milling. The average particle size of the milled powders as determined from TEM analysis was about 5·96 nm. Analysis of all the milled powders using X-ray diffraction method showed single phase perovskite structure. The density variation of the ceramics with sintering temperature has been studied by sintering the samples at different temperatures. Density variation results show that 1350°C is the optimum sintering temperature for tin-doped barium titanate ceramics. SEM micrographs show high density and increasing trend of grain size with increasing content of Sn. The ferroelectricity decreases with increasing concentration of Sn. The electromechanical coupling coefficient also decreases with increasing Sn content corroborating decreasing trend of ferroelectricity. The bipolar strain curves show piezoelectric properties of the prepared ceramics.     

Preparation of Lanthanum-Doped Pb(Zr,Ti)O3 Ceramics Sheets by Tape Casting

The physical and electrical properties of lanthanum doped Pb（Zr,Ti）O3 ceramic sheets （PLZT） which were prepared by tape casting method were carried out. Tape casting of lanthanum modified PZT was performed using commercial cellulose acetate binders and poly（ethylene glycol） plasticizers in ethanol solvent. Tapes from these slips were casted on a polymer substrate. The PLZT green tapes were stacked for 5 units and sintered in air at 1050℃ for 1 h with heating rate 5℃/min. SEM micrographs show that the tape is dense （90.26% of theoretical density） and rather uniform with grain size of approximately 1.1 9 m. The dielectric permittivity and loss tangent of PLZT ceramics as a function of temperature at 1 kHz suggest that the compounds exhibit a phase transition of diffuse type. The transition temperature （Tm ） and piezoelectric coefficient （ d33 ） were 110℃ and 117 pC/N, respectively.     

90‡ domain reversal in Pb(Zr x Ti1−x )O3 ceramics

A simple and direct method has been proposed, which may be used for quantitatively distinguishing the mechanisms of domain reorientation processes in polycrystalline materials. Using this method, the 90 domain reorientation in the Pb(Zr _x Ti_1–x )O₃ ceramic under an electric field was examined through the X-ray diffraction analysis. It was found that polarization switching in the PZT ceramic with a composition near the morphotropic phase boundary, is predominantly controlled by the two successive 90 domain processes rather than only the 180 domain reversal process. Experimental results also indicate that the coercive field of ferroelectric ceramics is related to the cooperative deformation associated with each grain. This cooperative deformation arises from the 90 domain-reversal process.     

Preparation process,microstructure and dielectric properties of Na0.5La0.5Cu3Ti4O12 ceramics by a sol–gel method

Effect of concentration, water content (molar ratio of the water and titanium) and pH value of the sol, and sintering temperatures and holding time on microstructure and dielectric properties of Na_0.5La_0.5Cu₃Ti₄O₁₂ (NLCTO) ceramics by a sol–gel method were investigated in detail, respectively. It is found that the optimum concentration, the molar ratio of the water and titanium, and pH value of the sol were 1.00 mol/L, 11.0, and 0.3, respectively. The NLCTO ceramics sintered at 1,080 °C for 10 h exhibited more homogeneous microstructure, higher dielectric constant (about 1.1–1.8 × 10⁴) and lower dielectric loss (about 0.051–0.064 at 1–10 kHz). The higher dielectric constant of the NLCTO ceramics might be due to the internal barrier layer capacitor effect. The NLCTO ceramics prepared by the sol–gel method showed two kinds of dielectric relaxation at higher temperature by electric modulus analysis, and two relaxation activation energy values were obtained.     

Effects of preferred orientation on the piezoelectric properties of Pt/Pb(Zr0.3Ti0.7)O3/Pt thin films grown by sol–gel process

Tetragonal lead zirconate titanate (PZT) films with different orientations and 200 nm film thicknesses were prepared on platinized silicon substrates. Types of substrate and control of thermal processes, such as layer-by-layer and one-crystallization heat treatments, result in highly (111) or (100)-oriented PZT films. The piezoelectric, dielectric, and ferroelectric properties of polycrystalline PZT films have been investigated as a function of preferred orientation. The property difference between (111) and (100)-oriented films appears to be induced by the effect of ferroelastic domain existence (90° domain in tetragonal composition). From a modified phenomenological equation, the higher electrostrictive coefficient value of 5.6 × 10⁻² m⁴/C² for (100)-oriented PZT may be responsible for the larger piezoelectric coefficients in (100)-oriented polycrystalline PZT films of 44 pm/V in comparison to (111)-oriented PZT films with about 3.1 × 10⁻² m⁴/C² of Q ₃₃ and 40 pm/V of d _33,f . It was also observed that two (100)-oriented films prepared by different heat treatments showed different values in piezoelectric, dielectric, and ferroelectric properties even though only (100) orientation was characterized for both cases. This process-induced difference may also play an important role in determining both intrinsic and extrinsic contribution to the properties, even though these parameters seem to be more responsible for extrinsic components, such as domain wall motion.     

Effect of Ni doping on the microstructure and high Curie temperature ferromagnetism in sol–gel derived titania powders

Undoped, 0.05 and 0.5 mol% Ni-doped TiO₂ powders were prepared by a modified sol–gel route. The doping effects on the microstructure and magnetism for the powdered samples have been systematically investigated. Doping of Ni in TiO₂ inhibited rutile crystal growth. The probable reason for this is discussed on the basis of band calculation based analysis of electronic structures of 3d transition metal-doped TiO₂ and the energetic, transformation kinetics and phase stability of anatase over rutile as the function of particle size. Room temperature ferromagnetism (RTFM) with the saturation magnetization of 12 m emu g⁻¹ and Curie temperature as high as 820 K is observed only in case of 0.05 mol% Ni:TiO₂ powdered sample, whereas undoped TiO₂ was diamagnetic and 0.5 mol% Ni:TiO₂ was paramagnetic in nature. The role of any magnetic impurity or any Ni metal in the origin of the RTFM has been ruled out by energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and high resolution TEM (HRTEM) analysis, whereas magnetic force microscopy (MFM) established the presence of magnetic domains, supporting the intrinsic diluted magnetic semiconductor behavior. The observed ferromagnetism has been attributed to the spin ordering through exchange interaction between holes trapped in oxygen orbitals adjacent to Ni substitutional sites.     

Effects of annealing ambient on ferroelectric properties and surface chemistry of sol–gel derived Bi3.25La0.75Ti3O12 thin films

In this work, Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films were prepared by sol–gel coatings followed by rapid thermal annealing in Ar or O₂ ambient. The correlation among annealing ambient, ferroelectric characteristics and surface chemistry of the BLT thin films were investigated. The BLT thin film annealed in Ar showed weaker crystallization, less dense surface and smaller polarization value than that annealed in O₂. After 10⁹ cycles, the remnant polarization of the BLT film annealed in Ar decreased to 83.5 % of the initial value while it remained 89.5 % for the sample annealed in O₂. X-ray photoelectron spectroscopy results indicated the inferior fatigue characteristics of the sample annealed in Ar was the comprehensive result of oxygen vacancies vicinity to Bi and Ti ion in the thin film.     

Fabrication and electrical properties of textured Ba(Zr0.2Ti0.8)O3–(Ba0.7Ca0.3)TiO3 ceramics using plate-like BaTiO3 particles as templates

Plate-like BaTiO₃ (BT) particles were used as templates to fabricate grain-oriented Ba(Zr_0.2Ti_0.8)O₃–(Ba_0.7Ca_0.3)TiO₃ (BZT–BCT) ceramics. The effects of the sintering temperature and the soaking time on the microstructure and electrical properties of the textured BZT–BCT ceramics were investigated. The results show that textured ceramics were obtained with orientation factor better than 0.5. The textured BZT–BCT ceramics have rhombohedral and tetragonal structures. Terrace morphology can be observed in the grains and the mechanism of grain growth is multi-nucleation multilayer growth. The T_R–T and T_C of BZT–BCT ceramics shift to higher temperature as the soaking time increases. Textured structures improve the dielectric, piezoelectric properties, and weaken the dielectric relaxor characteristics. When BZT–BCT ceramics sintered at 1,500 °C for 20 h, the maximum piezoelectric coefficient of 350 pC/N can be obtained.     

Piezoelectric properties of Nb2O5 doped and MnO2—Nb2O5 co-doped Pb(Zr0.53Ti0.47)O3 ceramics

The effects of Nb₂O₅ addition and MnO₂Nb₂O₅ co-addition on the piezoelectric properties of Pb(Zr_0.53Ti_0.47)O₃ (PZT) ceramics are investigated. When Nb₂O₅ is added to PZT, the planar coupling factor (K _p) significantly increases but the mechanical quality factor (Q _M) as well as the electrical quality factor (Q _E) decreases. When MnO₂ and Nb₂O₅ are co-doped, Q _M increases remarkably while K _p rarely changes. This increase in Q _M is ascribed to the domain pinning by Mn as is the case of previously reported MnO₂-doped PZT, and the negligible change in K _p is ascribed to the barely changed tetragonality. Even though MnO₂-Nb₂O₅ co-doped PZT shows a smaller induced strain than that of Nb₂O₅- doped PZT, excellent temperature stability is obtained. It is shown that MnO₂Nb₂O₅ co-doped PZT may be a very suitable material for high-power piezoelectric actuators because of its high K _p, Q _M and Q _E, its low dielectric constant and its excellent temperature stability.