Simultaneous preparation and densification of lead magnesium niobate-based ferroelectrics

Abstract

Ferroelectric lead titanate-doped lead magnesium niobate ceramics have been prepared and densified simultaneously by a new reaction sintering process. At low temperatures, the pyrochlore phase is firstly formed, which induces the expansion of the specimens. When the perovskite phase begins to produce at elevated temperatures, the specimens rapidly shrink, indicating the occurrence of reaction sintering. After sintering at 850°C, monophasic Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ solid solutions with high density are obtained. With an increase in the doping amount of PbTiO₃, the maximum dielectric permittivity and the Curie temperature increase; however, the relaxor characteristics of Pb(Mg_1/3Nb_2/3)O₃ become weakened. With the addition of 15 mol% PbTiO₃, the maximum dielectric permittivity is over 25000 at 1 kHz. It is concluded that monophasic and densified Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ with high dielectric permittivity are successfully prepared by the newly developed reaction sintering process.     

Processing and properties of nanocrystalline Pb(Sc0.5Ta0.5)O3, Pb(Sc0.5nb0.5)O3 and Pb(Mg1/3Nb2/3)O3 films produced by RF-sputtering from ceramic targets

Abstract

Nanocrystalline thin films of different relaxor materials, namely Pb(Sc_0.5Ta_0.5)O₃ (PST), Pb(Sc_0.5Nb_0.5)O₃(PSN), Pb(Mg_1/3Nb_2/3)O₃(PMN) have been produced by RF-sputtering to investigate whether it will affect their dielectric properties if their grain size is reduced to the dimensions known from their nanodomains. The XRD shows that the amorphous film crystallizes in pyrochlore structure at lower temperatures and short times. Annealing at higher temperatures and far longer time intervals leads to an increasing amount of perovskite phase with a grain size in the nanometer range. These results including dielectric measurements will be presented and discussed.     

Dielectric and piezoelectric properties of (0.90-x) PIN-xPT-0.10PZ ternary system near morphotropic phase boundary

The (0.90-x)Pb(In_1/2Nb_1/2)O₃-xPbTiO₃-0.10PbZrO₃ (PINTZ10) ceramics are prepared by solid state reaction and their structural, dielectric and piezoelectric properties near morphotrophic phase boundary (MPB) has been examined systematically. The structure undergoes a gradual change from rhombohedral to tetragonal when the PbTiO3 content (x) is increased. From the frequency and temperature dependent dielectric measurement it is found that the dielectric relaxation (ΔT) decreases with Ti⁴⁺ substitution. Even though the MPB of this ternary system is formed with lower PT content (0.62PIN-0.28PT-0.10PZ), the substitution of Zr⁴⁺ in the B site maintains the transition temperature (T_m) at 300 °C resembling its binary, 0.67PIN-0.37PT. The higher saturation polarization obtained for x?=?0.27 and the high piezoelectric co-efficient obtained for x?=?0.29 substantiate the existence of MPB between these two compositions.     

Synthesis, formation and characterization of lead indium niobate–lead titanate powders

In this study, powders of lead indium niobate–lead titanate (1???x)Pb(In_1/2Nb_1/2)O₃–(x)PbTiO₃ (PINT) binary system near the morphotropic phase boundary (MPB) composition with x?=?38 mol% PbTiO₃ are synthesized with the conventional mixed oxide and the wolframite methods via a rapid vibro-milling technique for the first time. The preparation method and calcination temperature have been found to show pronounced effects on the phase formation behavior of the PINT powders. The stabilized perovskite phase form of PINT can be synthesized by the wolframite method, while precursor phases are still found in powders prepared by the conventional method. Finally, this study shows that the rapid vibro-milling mixing technique is effective in preparing the phase pure perovskite of PINT powders.     

Stability of perovskite-type clusters in melts for relaxor ferroelectric crystal growth

Relaxor ferroelectric single crystals with perovskite structure were novel materials which might revolutionize some applications in medical ultrasonic imaging, telecommunication and ultrasonic devices. But during crystal growth and melt solidification, pyrochlore-type phase presented now and then, which reduced the integrality and properties of ferroelectric single crystals. This work dealt with the stability of perovskite-type clusters in melts for relaxor ferroelectric crystal growth by quenching and slow cooling. Differential thermal analysis (DTA) and X-ray diffraction (XRD) were employed to ascertain the transformation temperature between perovskite-type and pyrochlore-type clusters. Investigated results indicated that clusters in Pb(Mg_1/3Nb_2/3)O₃–32PbTiO₃ (PMN–32PT) melt which was under suitable temperature and prepared by proper pre-synthetic method were all and singular of perovskite-type structure, which established the fundament of PMN–32PT relaxor ferroelectric crystal growth from melts by Bridgman method. Whereas, clusters in Pb(Zn_1/3Nb_2/3)O₃–9PbTiO₃ (PZN–9PT) melt were of perovskite-type structure, pyrochlore-type structure, homologous PbO structure or homologous ZnO structure. During crystal growth from melts by Bridgman method, the pyrochlore phase always appeared.     

Piezoelectric ceramics and single crystals for ultrasonic medical transducers

Complex system ceramics Pb(Sc_1/2Nb_1/2)O₃-Pb (Mg_1/3Nb_2/3)O₃-Pb(Ni_1/2Nb_1/2)O₃-(Pb_0.965,Sr_0.035)(Zr,Ti) O₃(PSN-PMN-PNN-PSZT abbreviated to PSMNZT) with extremely high dielectric constants, ε₃₃ ^T /ε₀ and ε₃₃ ^S /ε₀, have been synthesized by the conventional technique and the dielectric and piezoelectric properties of the ceramics have been investigated for ultrasonic medical transducers. On the other hand, relaxor-PbTiO₃ single crystals (SCs) of xPb(In_1/2Nb_1/2)O₃-yPb(Mg_1/3Nb_2/3)O₃-zPbTiO₃ (PIN-PMN-PT abbreviated to PIMNT 100x/100y/100z) with high phase transition temperature between rhombohedral and tetragonal phase, T _rt , and high Curie temperature, T _c , have been investigated for medical array transducers in order to overcome the shortcomings of the binary SCs such as 0.91Pb(Zn_1/3Nb_2/3)O₃-0.09PbTiO₃ (PZNT91/9) and 0.68Pb(Mg_1/3Nb_2/3)O₃-0.32PbTiO₃ (PMNT68/32). Moreover, the pulse echo characteristics of the ultrasonic probes using the piezoelectric ceramic and piezoelectric SC are discussed on the basis of simulation employing Mason’s model in this paper.     

Electromagnetic Wave Absorbing Properties of High-Permittivity Ferroelectrics Coated with ITO Thin Films of 377 Ω

For the aim of thin electromagnetic wave absorbers used in quasi-microwave frequency band, this study proposes the high-permittivity ferroelectrics of quarter wavelength thickness (/4 spacer) coated with ITO thin film of 377 /sq (impedance transformer). For high-permittivity dielectrics, BaTiO₃ (BT), 0.9Pb(Mg_1/3Nb_2/3)O₃-0.1PbTiO₃ (PMN-PT) and 0.8Pb(Mg_1/3Nb_2/3)O₃-0.2Pb(Zn_1/3Nb_2/3)O₃ (PMN-PZN) are prepared by conventional ceramic processing technique. The ferroelectric materials show high dielectric constant and dielectric loss in microwave frequency range and their dominant loss mechanism is considered to be domain wall relaxation or dynamics of polar clusters. The microwave absorbance (determined at 2 GHz) of BT, PMN-PT and PMN-PZN are found to be 65% (at a /4 thickness of 3.5 mm), 20% (2.5 mm) and 37% (2.5 mm), respectively. By coating ITO thin films on the ferroelectric substrates with a thickness of /4, the microwave absorbance is greatly improved. Particularly, when the sheet resistance of ITO films is closed to 377 /sq, the reflection loss is reduced to –20 dB (99% power absorption). This is attributed to the wave impedance matching led by ITO thin film combined with a /4 thickness of high-permittivity dielectric spacer. It is, therefore, successfully proposed that the ITO/ferroelectrics structure with controlled electrical properties and thickness can be useful as thin microwave absorbers used in quasi-microwave frequency band.     

Synthesis and characterizations of the (1 − x)Pb(Sc1/2Nb1/2)O3–xPbTiO3 solid solution ceramics

We report a systematic study of the (1???x)Pb(Sc_1/2Nb_1/2)O₃–xPbTiO₃ (PSN–PT) solid solution in the form of ceramics with compositions at or near the morphotropic phase boundary (MPB) region (0.35?≤?x?≤?0.50). The PSN–PT ceramics have been synthesized by an improved two-step wolframite precursor method. The synthetic process has been optimized in terms of calcining and sintering conditions. Both dielectric permittivity measurements and differential scanning calorimetry (DSC) show a clear peak at T _C, at which the transition from the paraelectric to ferroelectric phase takes place. Interestingly, the solid solution of the MPB compositions displays a T _C?>?200 °C, i.e. higher than the T _C of the Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ and Pb(Zn_1/3Nb_2/3)O₃–PbTiO₃ solid solutions, making the PSN–PT system very promising piezoelectric and ferroelectric materials for high-temperature applications. A dielectric maximum as high as 50,000 is obtained for the 0.65PSN–0.35PT ceramic with losses smaller than 0.05. The values of the remnant polarization and the strain level of the PSN–PT ceramics are comparable to those of the PZT ceramics.     

Surface acoustic wave properties in 0.955Pb(Zn1/3Nb2/3)O3-0.045PbTiO3 multidomain single crystal poled along [001]c

Surface acoustic wave propagation in a 0.955Pb (Zn_1/3Nb_2/3)O₃-0.045PbTiO₃ multidomain single crystal poled along [001]_c has been analyzed theoretically using Christoffel wave equations. From the measured experimental data, the orientational dependence of surface acoustic wave phase velocities, electromechanical coupling coefficients and power flow angles was calculated. The results showed that surface acoustic wave propagations of 0.955Pb (Zn_1/3Nb_2/3)O₃-0.045PbTiO₃ are poor than 0.93Pb(Zn_1/3Nb_2/3)O₃-0.07PbTiO₃ crystal slightly. However, the 0.955Pb (Zn_1/3Nb_2/3)O₃-0.045PbTiO₃ single crystals have higher rhombohedral-tetragonal phase transition temperature and much stabler electromechanical properties. This may expand applications range of SAW devices.     

Lead-free (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)<Subscript>0.95</Subscript>(LiSb)<Subscript>0.05</Subscript>Nb<Subscript>0.95</Subscript>O<Subscript>3</Subscript>-BaTiO<Subscript>3</Subscript> piezoceramics

Lead-free (1-x)(K_0.5Na_0.5)_0.95(LiSb)_0.05Nb_0.95O₃-xBaTiO₃ (abbreviated as (1-x)KNNLS-xBT) piezoceramics were synthesized by conventional solid state sintering and the effect of BaTiO₃ on the microstructure, dielectric and piezoelectric properties was investigated. It was found that both orthorhombic-tetragonal (T _O-T) and tetragonal-cubic (T _C) phase transition temperatures decreased obviously with increasing BaTiO₃ content. Although proper amount of BaTiO₃ facilitated the sintering of (1-x)KNNLS-xBT ceramics, the addition of BaTiO₃ affected the relaxor behavior slightly and it was not beneficial to improve piezoelectric strain coefficient d ₃₃, remnant polarization P _r and piezoelectric coupling constant k _p.     

Application of spark plasma sintering for growing dense Pb(Mg1/3Nb2/3)O3–35 mol% PbTiO3 single crystal by solid-state crystal growth

This study examined the effect of spark plasma sintering (SPS) on the densification behavior and resulting dielectric and piezoelectric properties of Pb(Mg_1/3Nb_2/3)O₃–35 mol% PbTiO₃ ceramics with a 5 mol% excess of PbO. Through normal sintering at 1200^∘C, the density of the specimen reached only 92% of the theoretical density (TD). However, with the SPS treatment, the density of the PMN-PT ceramics increased to more than 99% of the TD at 900^∘C, and maintained over 98% of the TD during subsequent heat-treatment at 1200^∘C for 10 h. The increased density of the Pb(Mg_1/3Nb_2/3)O₃–35 mol% PbTiO₃ ceramics resulted in an improvement in the dielectric and piezoelectric properties. The SPS treatment was also successfully applied to the densification of a PMN-PT single crystal grown on a BaTiO₃ seed crystal using a solid-state crystal growth (SSCG) process.     

Niobium doping effects and ferroelectric relaxor behavior of bismuth lantanium titanate

Ferroelectrics Bi_3.25La_0.75(Ti_3−x Nb_x)O₁₂ (BLTN, x = 0∼ 0.1) solid solution systems were prepared, and Nb doping effects and relaxor behaviors were investigated. The BLTN single phases were confirmed by XRD. The phase transition temperature decreased as the Nb content increased, and the corresponding dielectric constant maximum broadened. The temperature T _m of the dielectric maximum depended on frequency and increased, which indicate that the relaxor behavior was caused by Nb substitution. The substitution of Nb for Ti ions affected the degree of disorder and modified the dielectric properties from those of normal ferroelectrics to relaxor ferroelectrics.     

Dielectric properties of Pb[(Mg1/3Nb2/3),Ti]O3 with Bi modification

Bi(Mg_2/3Nb_1/3)O₃ was partially substituted into a Pb(Mg_1/3Nb_2/3)O₃⋅PbTiO₃ perovskite system and resultant changes in the phase developments and dielectric properties were investigated. Two major structures of columbite and rutile, along with a small fraction of Mg₄Nb₂O₉ (α-Al₂O₃ structure), were developed in the B-site precursor system, whereas only a perovskite was observable after the addition of PbO and Bi₂O₃. The replacement of Bi for Pb resulted in a great reduction in the maximum dielectric constants as well as a substantial decrease in the dielectric maximum temperatures.     

RELAXATIONAL PROPERTIES OF LAYERED FERROELECTRICS CaBi1.5 La0.5Nb2O9

ABSTRACT

CaBi_1.5La_0.5Nb₂O₉ ceramics were prepared by a conventional solid-state reaction method. Their structure and dielectric properties were investigated. X-ray diffraction analysis indicated that single phase layered perovskites were obtained. Dielectric studies demonstrated that CaBi_1.5La_0.5Nb₂O₉ is characteristic of relaxor ferroelectrics. The dielectric relaxation of CaBi_1.5La_0.5Nb₂O₉ was modeled using the Vögel-Fulcher relationship, and the dielectric relaxation in CaBi_1.5La_0.5Nb₂O₉ is found to be analogous to a spin glass with thermally activated polarization fluctuations above a static freezing temperature.     

Ferroelectric properties of Al and Nb doped PbTiO3 thin films prepared by chemical solution deposition process

Abstract

Thin films of pure and acceptor (Al) as well as donor (Nb) doped PbTiO₃ were prepared using a chemical solution deposition method. The nominal compositions of the solutions were equivalent to those of PbTiO₃, Pb(Ti_0.95Al_0.95)O₃ and Pb(Ti_0.95Nb_0.05)O₃, respectively. In the case of PbTiO₃, the remanent polarization amounted to 43 μC/cm², but the shape of the hysteresis curve was round. On the other hand, Al and Nb doped PbTiO₃ thin films exhibited well-saturated P-Ehysteresis curves. The shape of these curves was slim compared to that of PbTiO₃. The remanent polarization of the Pb(Ti_0.95Al_0.05)O₃ and Pb(Ti_0.95Al_0.05)O₃ thin films amounted to 18 and 15 μC/cm², respectively, and the coercive field decreased in comparison with that of PbTiO₃. The leakage currents of the PbTiO₃, Pb(Ti_0.95Al_0.05)O₃ and Pb(Ti_0.95Al_0.05)O₃ thin films were 7.68x10^?3, 3.21x10^?6 and 6.58x10^?4 A/cm², respectively, at+10V.     

Domain Wall Dynamics Near the Phase Transition in PZN-9%PT

To investigate the paraelectric–ferroelectric phase transition in relaxor Pb(Zn_1/3Nb_2/3)O₃-9% PbTiO₃, correlations and scaling relations were measured from the domain structure of single crystals near the Curie temperature using a multifractal analysis. The dynamics of the domain walls were observed in (100) platelets using polarized light microscopy. The complexity of the domain wall distribution was evaluated by means of its fractal dimension and singularity spectrum. The changes in the energy state of the samples are assessed by measuring changes of the spatial distribution of the walls as a function of temperature; this can be used to estimate the specific heat.     

Fitting and analyzing the dielectric spectra of Pb(Mg1/3Nb2/3)O3-xPbTiO3 ceramics and single crystals

The dielectric spectra of Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃(PMN-xPT) ceramics and single crystals with different PbTiO₃(PT) content were fitted and analyzed with dual mechanisms model proposed by Cheng et al. Two polarization processes were proposed in this model, one is related to flips of polar regions and the other associates with the breathing behavior of frozen polar regions. The fitted results showed that the weight factors of contribution of dielectric response from the two mechanisms near T _m varied with the different measuring frequency and PT content. These results can explain why the modeling parameters of T _m and ω to Vogel–Fulcher relation show unlike results in different frequency regions.     

Study of the Electrical Properties of Pb(Mg,Ni)1/3Nb2/3O3-PbTiO3 System Across the Morphotropic Phase Boundary

Phase transitional behavior and electrical properties of (1 – x)Pb(Mg,Ni)_1/3Nb_2/3O₃-xPbTiO₃ ceramics (PMNN-PT with Mg/Ni = 1:1, x = 0.20–0.40) across the morphotropic phase boundary (MPB) were examined. X-ray diffraction and dielectric measurement reveal that two phases, pseudocubic and tetragonal phases, coexist in the composition range x = 0.30–0.36. The maximum d ₃₃ (about 570 pC/N) was observed at the composition x = 0.32–0.34. Dielectric and ferroelectric properties exhibit abnormal high near the MPB. An unusual peak shoulder occurred in the dielectric measurement upon thermal cycling for poled samples. This phenomenon was considered to be associated with the macro to micro domain transition and depolarization.     

Development and Electromechanical Properties of Multimaterial Piezoelectric and Electrostrictive PMN-PT Monomorph Actuators

Monolithic multimaterial monomorphs, comprised of varying ratios of piezoelectric 0.65Pb(Mg_1/3 Nb_2/3)O₃-0.35PbTiO₃ to electrostrictive 0.90Pb(Mg_1/3Nb_2/3)O₃-0.10PbTiO₃, have been co-fired at 1150^∘C. The relative permittivity, displacement, and polarization hysteresis were investigated for varying ratios of piezoelectric to electrostrictive material. The permittivity of the 1:1 multimaterial monomorphs followed the dielectric mixing laws, showing a dielectric constant of 5,500 at room temperature. The P-E hysteresis loop of the 1:1 sample exhibited a maximum and remnant polarization slightly less than the piezoelectric PMN-PT 65/35, but higher than the electrostrictive PMN-PT 90/10. Displacement was found to be higher for the 3:1 monolithic monomorph actuators, reaching 76 μ m at 6 kV/cm. The results indicate that by minimizing the electrostrictive layer thickness the tip displacement can be substantially increased while maintaining a lower hysteresis than that of the purely piezoelectric counterpart.     

Dielectric Properties and Phase Transition Behavior of xPMN-(1 − x)PZT Ceramic Systems

The dielectric properties and phase transition behavior of the pseudo-ternary xPb(Mg_1/3Nb_2/3)O₃-(1 – x)Pb(Zr,Ti)O₃ solid solution system were investigated as a function of the Pb(Mg_1/3Nb_2/3)O₃ (PMN) content and Ti/Zr ratio for selected compositions. The investigations have demonstrated a general trend in broadening of the phase transition and increasing diffusivity with increasing PMN content. For the morphotropic phase boundary (MPB) compositions, the dielectric permittivity maximum, its temperature (T _m) and the Curie-Weiss constant were found to decrease with increasing Mg_1/3Nb_2/3 concentration. When a Ti/Zr ratio was constant and equal to 53/47, temperature-dependent investigations demonstrated that the dielectric parameters involved in a modified Curie-Weiss law increase monotonically with increasing PMN content and T _m moves toward room temperature with average rate of –4.1°C/mol% as well. A phase transition in 0.5PMN-0.5Pb(Zr_0.47Ti_0.53)O₃ and 0.25PMN-0.75Pb(Zr_0.60Ti_0.40)O₃ ceramic systems exhibited a diffused behavior with a characteristic frequency dependence of T _m. From pyroelectric measurement, an unusual spontaneous polarization behavior at about 215 K is reported for some MPB compositions.