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.     

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.     

Epitaxial ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 thin films on La0.7Sr0.3MnO3 bottom electrode

Epitaxial (001)-oriented 0.7Pb(Mg_0.33Nb_0.67)O₃-0.3PbTiO₃ (PMN-PT) thin films were deposited by pulsed laser deposition on vicinal SrTiO₃ (001) substrates using La_0.7Sr_0.3MnO₃ as bottom electrode. Detailed microstructural investigations of these films were carried out using X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). Polarization-field hysteresis curves were measured at room temperature. Spontaneous polarization P _s , remnant polarization P _r and coercive voltage V _c were found to be 25 μC/cm², 15 μC/cm² and 0.81 V, respectively. Field dependent dielectric constant measurements exhibited butterfly shaped curves, indicating the true ferroelectric nature of these films at room temperature. The dielectric constant and the dielectric loss at 100 kHz were found to be 238 and 0.14, respectively. The local piezoelectric properties of PMN-PT films were investigated by piezoelectric force microscopy and were found to exhibit a local piezoelectric coefficient of 7.8 pm/V.     

Electromechanical properties of PMN-PT thin films prepared by pulsed laser deposition technique

Abstract

Ferroelectric relaxor thin films of the composition 0.9Pb(Mg_1/3Nb_2/3)O₃-0.1PbTiO₃ (PMN-PT) were fabricated by pulsed laser deposition technique on Pt/Ti/SiO₂/Si(100) substrates using a La_0.5Sr_0.5CoO₃ film as a template layer. The films were polycrystalline with random orientation of the grains. Electromechanical properties of the films were evaluated by a sensitive interferometric technique as a function of the dc and ac electric fields and frequency. Experimental results show that the effective piezoelectric coefficient d₃₃ can be tuned over a wide range of magnitudes by varying dc bias fields. A small hysteresis and a low remanent d₃₃ were observed, which favor the use of PMN-PT films in electric field-controlled micromechanical devices. The maximum d₃₃ ranged from 50 to 100 pm/V, depending on the thickness of the films and frequency. The piezoelectric properties are explained based on the expression for the electrostriction biased by polarization. At low electric field, strain is proportional to the square of electric field, while at higher fields it can be better described as the polarization squared. The asymmetry of the strain response in PMN-PT films is attributed to the polarization offset appearing due to the different electrode materials.     

Preparation of Pb(Mg1/3Nb2/3)O3-PbTiO3 thin films by MOCVD using ultrasonic nebulization

Thin films of Pb(Mg_1/3,Nb_2/3)O₃ (PMN) and Pb(Mg_1/3,Nb_2/3)O₃-PbTiO₃ (PMN-PT) were fabricated on Si and Pt/Ti/SiO₂/Si substrates by MOCVD using ultrasonic nebulization and their characteristics were investigated. PMN-PT films deposited at 350^∘C were annealed in a RTA (Rapid Thermal Annealing) system at 650^∘C for 30 sec to improve the micostructural properties. The crystallographic properties of PMN-PT films strongly depend on the content ratio of PbTiO₃. The content of pyrochlore phase in PMN-PT films decreased with the increase of Ti content and nearly single phase perovskite films were obtained at the composition of 80PMN-20PT. The PMN-PT films with perovskite phase showed a typical butterfly type C-V curve which verifies the ferroelectricity and had the relative dielectric constant of about 60.     

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.     

Phase transition and piezoelectric response under electric field in PMN-PT crystals

The phase transition between the ferroelectric and relaxor states for (1-x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMN-PT) single crystals at low PT (x = 0.21) was identified using high-resolution X-ray diffraction. The characterization of the dielectric and pyroelectric currents determined the properties of the polar state. The temperature stability region of the polar phase was enlarged with increasing bias field, and the corresponding polarization and piezoelectric properties were enhanced. Non-linearity of the electric displacement and loss under high ac fields was investigated by laser interferometry at a frequency of 40 kHz well below the resonant frequency. A linear displacement was obtained up to a large alternating current-field of 125 V/mm with an almost negligible second order harmonic component. The optimal d₃₃ improvement was 1,339 pm/V found for the [001] orientation. Such disclosure of phase stability and enhanced performances under high external field will be useful to determine their practical applications for resonant power transducers and quasi-static actuators.     

Substituent Effects in 0.65Pb(Mg1/3Nb2/3O30.35PbTiO3 Piezoelectric Ceramics

Pb(Mg_1/3Nb_2/3O₃–-PbTiO₃ (PMN-PT) ceramics with base compositions close to the morphotropic phase boundary are potential materials for many applications such as transducers and actuators due to their high dielectric constants and electromechanical coupling factors. However, their dielectrical and mechanical losses are too high for high-power applications. In this paper, the dielectric and electromechanical properties of piezoelectric PMN-PT ceramics were investigated in specimens containing various A-site and B-site substituents with the goal of developing lower loss materials for wider applications. Emphasis was placed on various transition metal cation substituents of both lower and higher valences. Mn substituent was found to be the most promising substituent investigated for developing high power low loss piezoelectric PMN-PT ceramics.     

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.     

Fabrication of 0.655Pb(Mg1/3Nb2/3)O3-0.345PbTiO3 functionally graded piezoelectric actuator by tape-casting

A 0.655Pb(Mg_1/3Nb_2/3)O₃-0.345PbTiO₃ (PMN-0.345PT) functionally graded (FG) piezoelectric actuator was fabricated by tape-casting. The effects of sintering temperature on the physical and electrical properties of the PMN-PT ceramics were initially investigated. High dielectric and piezoelectric properties of d ₃₃?=?700pC/N, k _p?=?0.61, ??_r?=?4.77?×?103, tan???=?0.014, P _r?=?30.68 ??C/cm² were obtained for the specimens sintered at 1200°C. Compared with the traditional solid-state reaction, the properties of the ceramics were significantly enhanced by tape-casting. The new FG piezoelectric actuator consisted of four layers, and the variation of changes in their d ₃₃ and ?? _r were graded opposite the thickness direction. The relationship between displacement and voltage for the actuator was also determined, with the results showing that it was linear. The driving displacement of the free end of the actuator reached 430.668 ??m.     

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.     

Pb(Mg1/3Nb2/3)O3 and (1 − x)Pb(Mg1/3Nb2/3)O3 − xPbTiO3 Relaxor Ferroelectric Thick Films: Processing and Electrical Characterization

The lead magnesium niobate [Pb(Mg_1/3Nb_2/3)O₃ or PMN], and its solid solutions with lead titanate (PbTiO₃ or PT), are of great interest because of their high electromechanical properties. At large PMN content, these materials exhibit relaxor characteristics with large electrostrictive strains and a large permittivity, while compositions near the morphotropic phase boundary present very interesting piezoelectric properties. So far, properties of these materials in ceramic, thin film and single-crystal form have been investigated. In this paper, we report on preparation and properties of pyrochlore free PMN and 0.65PMN-0.35PT thick films (thickness = 10 to 20 m). The films were prepared from ethyl cellulose ink by screen printing on alumina substrate. The influence of various parameters, such as powder characteristics, inks formulation and films sintering conditions, on films densification are discussed. The dielectric and electromechanical properties of the films were examined. Relaxor-like behaviour was clearly demonstrated in PMN films. The maximum relative permittivity for PMN film was 10000 (at 0.1 kHz), which is lower than in bulk ceramics (17800 at 0.1 kHz) prepared under the same conditions. For 0.65PMN-0.35PT, the maximum relative permittivity was around 15500 against 24000 in the bulk. Several parameters, which might be responsible for the lower permittivity, are discussed. Poled 0.65PMN-0.35PT thick films exhibit relatively large piezoelectric response (d ₃₃ up to 200 pm/V) and unipolar strains approaching 0.1%, making these films of interest for various actuator and transducer applications.     

Estimation of energy density of PMN-PT ceramics utilizing mechanical stress

Abstract

Present study introduces an indirect measurement of energy density of (1-x)Pb(Mg_1/3Nb_2/3)O₃-(x)PbTiO₃ (PMN-PT) ceramics under compressive stress and electric field. The method works analogous to Olsen cycle which is a demonstration of a novel cycle converting mechanical energy into electrical energy. A large amount of electro-mechanical energy conversion can be achieved via this method. The ceramics were investigated under 0–75?MPa and 1–15?kV/cm of applied mechanical stress and electric field, respectively. A maximum energy density of 68?kJ/m³/cycle was achieved in 0.7PMN-0.3PT ceramic. The obtained result is significantly greater than that of linear piezoelectric phenomena.     

Study of the structure and electrical properties of PMN-PNN-PT ceramics near the morphotropic phase boundary

A series of Pb(Mg_1/3Nb_2/3)O₃-Pb(Ni_1/3Nb_2/3)-O₃-PbTiO₃ (PMN-PNN-PT) ceramics with compositions of (1–x)(0.67PMN-0.33PT)-x(0.64PNN-0.36PT) (x = 0.1–0.9) were synthesized using the columbite precursor method. The phase structures, as well as the dielectric and piezoelectric properties of the ceramics were investigated in detail. X-ray diffraction results demonstrate that all the samples possess a pure perovskite structure. It is found that the morphotropic phase boundary (MPB) region of the PMN-PNN-PT ternary system is located near the line connecting the MPBs of the PMN-PT and PNN-PT binary systems. A high value of the maximum dielectric constant (ɛ_m = 45540, at 1 kHz), together with a high value of the piezoelectric coefficient (d₃₃ = 780 pC/N), were obtained for the composition x = 0.2. The results show that a partial substitution of PNN-PT for PMN-PT can lead to improved electrical properties in this ternary system.     

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.     

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.     

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.     

Characteristics of PMW-PNN-PT-PZ thick films on various bottom electrodes

Characteristics of piezoelectric thick films on various bottom electrodes prepared by screen printing method were investigated. The composition of the ceramics used in this study was 0.01Pb(Mg_1/2W_1/2)O₃–0.41Pb(Ni_1/3Nb_2/3)O₃–0.35PbTiO₃–0.23PbZrO₃ + 0.1wt% Y₂O₃ +2.0 wt.%ZnO(PMW-PNN-PT-PZ). The Ag and the Ag-Pd electrodes were coated on SiO₂/Si substrate by screen printing method and Pt electrode was deposited on Ti/ SiO₂/Si substrate by DC sputtering system. The piezoelectric PMW-PNN-PT-PZ thick films were fabricated on each electrode and annealed by rapid thermal annealing (RTA). The PMW-PNN-PT-PZ piezoelectric thick films on Ag/SiO₂/Si has higher remanent polarization (P _r) of 22.4 μC/cm².     

Investigation of the BaTiO3–BaMg1/3Nb2/3O3 system: Structural, dielectric, ferroelectric and electromechanical studies

Lead-free (1?x) BaTiO₃ –x BaMg_1/3Nb_2/3O₃ ceramics with x?=?0.03, 0.04, 0.05 and 0.06 were prepared by solid-state synthesis. The effects of the Ba(Mg_1/3Nb_2/3)O₃ addition on the phase composition, dielectric and ferroelectric properties, as well as the electromechanical response of the classic ferroelectric BaTiO₃ were investigated. The room-temperature X-ray diffraction analyses of all the ceramics revealed a perovskite phase after sintering at 1300 °C with a composition-dependent symmetry. The samples with a lower concentration of Ba(Mg_1/3Nb_2/3)O₃, i.e., x?=?0.03 and 0.04, were tetragonal, while the samples with x?=?0.05 and 0.06 were found to be cubic. The result is in agreement with the dielectric, ferroelectric and electromechanical properties. With x increasing from 0.03 to 0.06 the temperature of the diffused maximum of the dielectric permittivity decreased from 348 K to 265 K. All the ceramics showed a large electromechanical response: the calculated room-temperature electrostrictive coefficient M ₃₃ of the sample with x?=?0.06 was 1.4 · 10^?16?m²/V², which is comparable to the value measured for Pb(Mg_1/3Nb_2/3)O₃ ceramics.     

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.