Phase coexistence in lead zirconate titanate solid solutions

This paper discusses the phenomena observed in the vicinity of the morphotropic phase boundary in Pb(Ti_1?x Zr_x)O₃ (PZT) solid solutions. The location of the boundary between the stable tetragonal ferroelectric phase and the stable rhombohedral ferroelectric phase is calculated, and an analytical expression for determining the concentration range of the possible coexistence of these phases is derived. According to the numerical estimates, the concentration range can be as much as 20 mol % lead zirconate. However, reliable experimental data in support of these estimates are as yet unavailable.     

Control of the properties of Pb(TixZr1-x )O3 solid solutions by external disturbances

The influence of x-ray irradiation to absorbed radiation doses D = (0.5?12) × 10⁸ rad on the properties of ferroelectric ceramic Pb(Ti_xZr_1?x )O₃ solid solutions with compositions close to the morphotropic phase boundary was studied. The effects of x-ray radiation on the electrical conductivity of ferroelectric ceramics are shown to differ with x ranging from 0.42 to 0.60. Using empirical equations and numerical techniques, quantitative relations are established between the composition, absorbed radiation dose, and electrical conductivity for Pb(Ti_xZr_1?x )O₃.     

X-ray study of the PZT solid solutions near the morphotropic phase transition

In the solid solutions Pb(Zr_xTi_1?x)O₃ it is stated that for x ? 0.55 there is a morphotropic phase change. Thermodynamically, it is expected that there will be a region of x, in which the two phases coexist and obey the leverage law. By X-ray diffraction, we found that the two phases coexist for x between 0.49 and 0.64. In this range the lattice parameters do not change, and the leverage law is obeyed. We conclude that an adequate explanation of the particular properties of the PZT solutions has to be found.     

Piezoelectric activities and domain patterns of orthorhombic Ba(Zr,Ti)O3 ceramics

Ba(Zr_xTi_1?x)O₃ (0.025 ≤ x ≤ 0.065) ceramics were prepared by conventional solid-state reaction method. Crystalline structures were analyzed by X-ray diffraction. It was shown that all the Ba(Zr_xTi_1?x)O₃ (0.025 ≤ x ≤ 0.065) ceramics were of orthorhombic phase at room temperature. Piezoelectric activities and domain patterns were investigated and compared with those of BaTiO₃ ceramic. All the Ba(Zr_xTi_1?x)O₃ ceramics showed nearly the same d₃₃ values of about 265 pC/N and the same domain width of about 220 nm. By comparing the grain sizes and domain width of the Ba(Zr_xTi_1?x)O₃ ceramics with those of BaTiO₃ ceramic, it is speculated that the variation of domain width with grain sizes in orthorhombic Ba(Zr_xTi_1?x)O₃ ceramics may be different with that in tetragonal BaTiO₃ ceramic. Besides domain width, the effective inertia mass of domain wall is also considered to be a very important factor that impacts the piezoelectric activities of the Ba(Zr_xTi_1?x)O₃ ceramics.     

In situ hot-stage transmission electron microscopy of Pb(Zr0.52Ti0.48)O3

The domain structure of Pb(Zr_0.52Ti_0.48)O₃ before and after hot-stage experiment has been studied. The influence of maximum temperature, heating and cooling rate on the domain configuration of Pb(Zr_{1? x} , Ti _x )O₃ with x = 0.40, 0.45, 0.48 and 0.55 was analysed. A reliable basis for further hot-stage experiments of Pb(Zr_1?x, Ti_x)O₃ has been established. The investigations revealed a temperature dependent appearance and disappearance of nano- and microdomains. The appearance of microdomains in the nano scale range during cooling, denoted as domain miniaturisation, and the time dependent recovering of the former domain structure, revealed that under specific experimental conditions the domain configuration is reversible.     

Synthesis of Zr-doped TiO2 templated from cloth and its photocatalytic activity

Biomorphic Zr-doped TiO₂ (Zr _x Ti_{1 ? x} O₂) with hierarchical micro- and nanostructures was successfully fabricated using cloth as the host template. We found that the resulting Zr _x Ti_{1 ? x} O₂ faithfully duplicated the morphologic microstructures of the initial cloth with grain size of about 10–50 nm. The photocatalytic activity of the as-prepared Zr _x Ti_{1 ? x} O₂ was examined by the degradation of rhodamine B in aqueous solution under simulated solar light, which showed that templates pretreated with NaOH solution followed by mixed acid and an appropriate amount of doped Zr (3 mol%) could significantly enhance the photocatalytic activities of Zr _x Ti_{1 ? x} O₂. This simple template method provides a cost-effective and ecofriendly route to synthesize other metal-doped semiconductor materials of predicted morphology.     

Crystallization kinetics and growth mechanism of Pb(Zr0.52·Ti0.48)O3 nanopowders

In this study, Pb(Zr_0.52·Ti_0.48)O₃ nanopowders were synthesized via sol–gel process. Particle morphology, crystalline phases and thermal behavior were characterized by scanning electron microscopy, X-ray diffraction and simultaneous thermal analyzer, respectively. The X-ray diffraction pattern showed perovskite phase clearly. The non-isothermal activation energy for the perovskite crystallization in Pb(Zr_0.52·Ti_0.48)O₃ gel powders was 224.91 kJ mol^?1. Both growth morphology parameter (n) and crystallization mechanism index (m) are close to 3.0, indicating that the bulk nucleation is dominant in the perovskite PZT formation. To determine dielectric properties, the calcined Pb(Zr_0.52·Ti_0.48)O₃ nanopowders were pressed using uniaxial press. It was found that the Pb(Zr_0.52·Ti_0.48)O₃ disks, by sintering at 1,200 °C for 2 and 10 h, and at 1 kHz frequency, had 966 and 1,490 of the dielectric constant, respectively.     

Concentration dependences of the properties of multicomponent PZT-based piezoelectric ceramics in the morphotropic transition range

The following three ternary PZT-based systems are studied in detail: 0.98Pb(Ti_xZr_1−x )O₃-0.02Pb(Nb_1/2Bi_1/2)O₃, 0.98(Pb_0.9727Sr_0.0273)(Ti_xZr_1−x )O₃-0.02Pb(Nb_1/2Bi_1/2)O₃ + 1 wt% PbO, and 0.98(Pb_0.9727Sr_0.0273)(Ti_xZr_1−x )O₃-0.02Pb(Nb_1/2Bi_1/2)O₃ + 2 wt % PbGeO₃, where 0.45 ≤ x ≤ 0.49 and the concentration step is Δx = 0.025. A number of concepts are formulated regarding the phase diagrams of PZT-type systems near the morphotropic transition. A scheme for real tetragonal-rhombohedral transformation is given. The maxima of the electrophysical characteristics of the solid solutions from the morphotropic range are shown to be caused mainly by an appearing intermediate phase. Analysis of the insulating, piezoelectric, and mechanical properties of the samples demonstrates that there is a group of solid solutions that are promising materials for high-temperature piezoelectric devices operating in the medium-frequency band.     

A TEM study of crystal and domain structures of Nb-Doped 95/5 PZT ceramics

95/5 PZT ceramics with compositions of Pb(Zr_1–x Ti _x )₃+1 wt% Nb₂O₅ (x=0.025 and 0.04) are studied with TEM. The coexistence of both ferroelectric (F) and antiferroelectric (AF) phases in one ceramic grain at room temperature is confirmed for these two compositions. The AF phase is mainly tetragonal, while a pseudo-cubic arrangement of AF polarization is also possibly present. When the Ti⁴⁺ concentration is increased, the F phase becomes predominant. Direct interfaces between F and AF domains can be observed, the former expands at the expense of the latter when bombarded by 200 keV electrons.     

The piezoelectric effect in Pb[(Fe1/3Sb2/3) x Ti y Zr z ]O3 ceramics

The piezoelectric properties of Pb[(Fe_1/3Sb_2/3) _x Ti _y Zr _z ]O₃ with x + y + z = 1, x = 0.1, y = 0.43–0.48 ceramics have been investigated over a broad temperature range using a resonance technique. The influence of modification of PZT normal ferroelectric synthesized near the morphotropic phase boundary by a relaxor Pb(Fe_1/3Sb_2/3)O₃ compound on its physical properties was studied. The coefficients s ₁₁, k ₃₁, and d ₃₁ were calculated from the parameters characterizing the behavior of damped harmonic oscillator in the vicinity of the piezoelectric resonance. Several anomalies of the piezoelectric coefficients have been found in the temperature range 300–600 K. Two diffuse phase transitions were observed in Pb[(Fe_1/3Sb_2/3) _x Ti _y Zr _z ]O₃. The anomaly near 530 K for y = 0.43 is responsible for the transition from the rhombohedral phase to the tetragonal one. For y > 0.44 this transition is found to be very diffuse and the coexistence of rhombohedral and tetragonal phases occurs. The observation of low piezoelectric activity confirms the existence of polar regions in Pb[(Fe_1/3Sb_2/3) _x Ti _y Zr _z ]O₃ above T _m.     

Effect of electric field on electrocaloric effect in Pb(Zr1 − xTix)O3 solid solution

A thermodynamic analysis is employed to investigate the intrinsic electrocaloric effect of Pb(Zr_1 − xTi_x)O₃ solid solution system under the different electric field. Theoretical analysis indicates that Pb(Zr_1 − xTi_x)O₃ system has the giant electrocaloric coefficient and the large adiabatic temperature change near its ferroelectric Curie temperature. The applied electric field decreases not only the electrocaloric coefficient but also its temperature dependence. Furthermore, it increases the adiabatic temperature change as well as its dependence of temperature. The temperature corresponding to the maximum of electrocaloric coefficient and adiabatic temperature change increases with the enhancement of electric field because of its first-order phase transition between ferroelectric phase and paraelectric phase.     

Ferroelectric properties of Pb(Zr1/2Ti1/2)O3–Pb(Zn1/3Nb2/3)O3 ceramics under compressive stress

Effects of compressive stress on the ferroelectric properties of ceramics in PZT–PZN system were investigated. The ceramics with a formula (1−x)Pb(Zr_1/2Ti_1/2)O₃–xPb(Zn_1/3Nb_2/3)O₃ or (1−x)PZT–(x)PZN (x = 0.1–0.5) were prepared by a conventional mixed-oxide method. The ferroelectric properties under the compressive stress of the PZT–PZN ceramics were observed at the stress levels up to 170 MPa using a compressometer in conjunction with a modified Sawyer–Tower circuit. It was found that with increasing compressive stress the area of the ferroelectric hysteresis (P–E) loops, the saturation polarization (P_sat), the remnant polarization (P_r), and the coercive field (E_c) decreased. These results were interpreted through the non-180° ferroelastic domain switching processes.     

An intermediate monoclinic phase and electromechanical interactions in xPbTiO3-(1−x)Pb(Zn1/3Nb2/3)O3 crystals

The elastic matching of phases in the vicinity of the morphotropic phase boundary in xPbTiO₃-(1?x)Pb(Zn_1/3Nb_2/3)O₃ crystals is investigated in an external electric field with strength E ‖ [001]. The field dependences of the unit cell parameters of the monoclinic phase are determined experimentally in the range 0≤E≤2 MV/m. The results obtained are used in analyzing specific features in the electromechanical properties of xPbTiO₃-(1?x)Pb(Zn_1/3Nb_2/3)O₃ crystals (0.08?x?0.09), in which the monoclinic phase is intermediate between the rhombohedral and tetragonal phases and can coexist with these phases. A correlation between the optimum volume concentrations of domains or twins in different two-phases states is revealed and interpreted for the first time.     

Dielectric properties of lead zirconate titanate films synthesized through oxidation of metal layers

Films of the composition Pb(Zr _x Ti_1?x )O₃ are prepared by magnetron sputtering of metal layers onto titanium substrates with subsequent heat treatment in an oxygen atmosphere. The electrical properties of the samples prepared are investigated using impedance spectroscopy in the frequency range from 10² to 5 × 10⁵ Hz at temperatures of 300–750 K. The temperature dependences of the permittivity and the dielectric loss tangent at different frequencies exhibit a behavior typical of ferroelectrics and indicate the occurrence of a ferroelectric phase transition at temperatures close to T = 663 K. Analysis of the imaginary part of the electric modulus has revealed two possible relaxation mechanisms. The activation energy for dc electrical conduction in the paraelectric phase is determined.     

Synthesis and physicochemical properties of Li2 Me x Zr1 − x O3 − δ (Me = Nb,Ti; x = 0.05, 0.1) solid solutions

Complex lithium metallates Li₂ Me _x Zr_{1 ? x} O_{3 ? δ} (Me = Nb, Ti, x = 0.05, 0.1) with iso-and heterovalent substitutions for Zr⁴⁺ ions in lithium zirconate are synthesized for the first time using a citrate technique. The inclusion of Ti⁴⁺ and Nb⁵⁺ ions in the crystal structure of Li₂ZrO₃ is confirmed by means of X-ray diffraction and NMR. It is shown that in the temperature range of 750–820 K, Li₂Ti_0.1Zr_0.9O₃ solid solution has higher conductivity than phases of undoped lithium zirconate.     

A method for determining a solid solution of the Pb(Hf1−yZry)1−xTixO3 type used for electromechanical energy conversion

The mechanical stress-forced Ferroelectric F→Antiferroelectric AF transition energy conversion is reviewed. The temperature-composition phase diagram of PbHf_1−xTi_xO₃+1%La₂O₃ is established. The composition of a suitable material such as a ternary solid solution of the Pb(Hf_1−yZr_y)_1−xTi_xO₃+1%La₂O₃ type, characterized by a low transition pressure, is theoretically determined by a graphic construction using the Goldschmidt factor. Experimental results on the prepared material are given.     

Ferroelectric studies for soft Gd-modified PZT ceramics

The polycrystalline samples of gadolinium-modified lead–zirconate–titanate (Pb_1?xGd_x (Zr_0.52Ti_0.48)_1?x/4O₃) (x?=?0, 0.07, 0.10 and 0.12) (PGZT x/52/48) ceramics near morphotropic-phase boundary were prepared using conventional solid-state reaction route. XRD patterns show the formation of single-phase compounds in rhombohedral crystal system. SEM textures of the samples reveal uniform grain distribution. Frequency and temperature dependence of dielectric constant of the materials indicates non-relaxor behavior and indication of the diffuse phase transition at higher values of Gd concentration. The temperature dependence of P–E loops confirms ferroelectricity in the materials. The piezoelectric studies of the samples show enhancement in piezoelectric coefficients on substitution of Gd at the Pb site.     

Development of perovskite and phase transition in lead cobalt niobate modified lead zirconate titanate system

Ferroelectric lead zirconate titanate–lead cobalt niobate ceramics with the formula (1 − x)Pb(Zr_1/2Ti_1/2)O₃–xPb(Co_1/3Nb_2/3)O₃ where x = 0.0–0.5 were fabricated using a high temperature solid-state reaction method. The formation process, the structure and homogeneity of the obtained powders have been investigated by X-ray diffraction method as well as the simultaneous thermal analysis of both differential thermal analysis (DTA) and thermogravimetry analysis (TGA). It was observed that for the binary system (1 − x)Pb(Zr_1/2Ti_1/2)O₃–xPb(Co_1/3Nb_2/3)O₃, the change in the calcination temperature is approximately linear with respect to the PCoN content in the range x = 0.0–0.5. In addition, X-ray diffraction indicated a phase transformation from a tetragonal to a pseudo-cubic phase when the fraction of PCoN was increased. The dielectric permittivity is remarkably increased by increasing PCoN concentration. The maximum value of remnant polarization P_r (25.3 μC/cm²) was obtained for the 0.5PZT–0.5PCoN ceramic.     

Dielectric and pyroelectric activities in Pb(Zr1−xTix)O3 ceramics: The role of the phase transition effects

Pure and Nb-doped Pb(Zr_1−xTi_x)O₃ (x = 0.47, 0.48, 0.50) ceramics were prepared by conventional solid-state reaction technique. Dielectric anomalies are observed in both kinds of samples near room temperature. The anomalies could be depressed by donor doping and prefer to be significant in ceramics with tetragonal crystallographic phase. Phase transition mechanism and domain wall pinning effect are proposed to explain this anomaly, and the former is considered as the dominated reason. Further results of the pyroelectric measurements confirm the existence of the ferroelectric–ferroelectric phase transition.     

Modified structure and electrical properties of BSZT doped KNN hybrid ceramic

Lead free (1?x)(K_0.5Na_0.5)NbO₃–x(Ba_0.9Sr_0.1)(Zr_0.1Ti_0.9)O₃ [(1?x)KNN–xBSZT] (x=0,0.02,0.04 and 0.06) ceramic were synthesized by a solid-state reaction method and the effects of BSZT doping on the electrical properties of KNN have been studied. X-ray diffraction (XRD) indicates that all the samples have single-phase perovskite structure and addition of BSZT forms a morphotropic phase boundary (MPB) i.e. the coexistence of orthorhombic and tetragonal phase in the region 0.02≤x≤0.04. Field emission scanning electron microscopy (FESEM) indicates the reduction in the grain size with the addition of BSZT. Small broadening in the dielectric peak arises at higher concentration of BSZT. The value of remnant polarization at x=0.04 is found to be higher than any other value of x except x=0 and also results in enhancement of dielectric constant at room temperature. Thereby it makes it useful for application at room temperature.