Добірка наукової літератури з теми "(x)BiScO3-(1-x)PbTiO3"

(1-x)BiScO3-xPbTiO3 (BSPT) based ferroelectric ceramics were prepared by conventional solid state process. X-ray diffraction analysis revealed that the morphotropic phase boundary (MPB) separating the rhombohedral and tetragonal phases for the BSPT system exited near x=0.62. It was found that the stability of perovskite structure of the BSPT system was improved with the increase of PbTiO3 content. For the 0.36BiScO3-0.64Pb1-ySryTiO3 (BSPST) system, because of higher amount of ionic bonding, the stability of perovskite structure for BSPT compounds containing strontium is larger than that of non-strontium compound.

In this study, (1–x)Bi0.5Na0.5TiO3– xBiScO3 (BNT–xBS) ceramics were synthesized via conventional solidstate reaction sintering. The effects of the BiScO3 content on the surface microstructure, energy storage, strain, and dielectric properties of BNT–xBS ceramics were systemically investigated. Results indicated that the phase structure of BNT–xBS ceramics transformed from the rhombohedral phase into the pseudo-cubic phase. As the increasing BiScO3 content, the average grain size decreased. BiScO3 destroyed the long-range ordered ferroelectric phase, enhancing relaxor behavior. Energy storage density initially increased and then decreased, reaching a maximum of 0.17 J/cm3 at x = 0.1. In addition, the maximum energy storage efficiency was 59% at x = 0.2. The BiScO3 content significantly affected the electrical properties of BNT– xBS ceramics.

he extent of BiInO₃ substitution in the perovskite system xBiInO(₃)-(1 - x)PbTiO₃ and the corresponding raise in the transition temperature were investigated using thermal analysis, dielectric measurements, x-ray diffraction, and electron microscopy. Maximum tetragonal perovskite distortion (c/a = 1.082) was obtained for x = 0.20, with a corresponding Curie temperature of 582°C. Phase-pure tetragonal perovskite was obtained for x less than or equal to 0.25. Compound formation after calcining mixed oxide powders resulted in agglomerated cube-shaped tetragonal perovskite particles, which could be fired to 94.7% of theoretical density (TD). Niobium-modified BIPT ceramics with PT contents of 80% and 85% were found to possess significantly lower dielectric loss at elevated temperatures, making it possible to polarize the materials. Piezoelectric properties were measured for a 1.5 mol% Nb -0.15BI-0.85PT composition with a transition temperature of 542°C; the longitudinal piezoelectric coefficient and coercive field were found to be 60 pC/N and 125 kV/cm, respectively. Compositions of xBiLaO₃-(1 − x)PbTiO₃ over the range 0 < x < 0.225 were calcined and sintered. Dielectric constant with temperature and differential scanning calorimetry measurements were in excellent agreement with respect to a Curie-like tetragonal to cubic transformations starting at 495°C for pure PbTiO₃, shifting to lower temperatures with increasing x. For compositions of x > 0.05, a second higher-temperature (∼600°C) endotherm, and matching dielectric anomaly, were consistently observed, for which there were no structural changes indicated by hot-stage x-ray diffraction. This transformation was interpreted to be similar to a Curie transformation in relaxor ferroelectrics in which localized segregation of B-site cations (below the resolution limit of x-ray diffraction) facilitated ferroelectric behavior.

Advanced piezoelectric ceramics are widely used as piezoelectric sensors, transducers, actuators, etc. Among the commercially viable piezoelectric systems, lead zirconate titanate, PbZr1-XTiXO3 (PZT) has dominated the market due to its superior properties and cost effective reproducibility. PZT exhibits enhanced piezoelectric properties in the vicinity of morphotropic phase boundary (MPB). The mechanism(s) associated with the anomalous piezoelectric response in the MPB systems is still a subject of considerable debate. The two contending theories in this regard are based on (i) field induced polarization rotation in single domain crystal and (ii) formation of a high density of low energy domain walls. Diffraction experiments in-situ with electric field can, in principle, give direct information about domain reorientation, lattice strain and phase transformation (if any) in ferroelectric systems. However, the combined effect of preferred orientation and severe overlapping of Bragg peaks in diffraction pattern of MPB compositions makes structural analysis very challenging. As a consequence, domain reorientation studies have mostly been reported for compositions away from the critical MPB, i.e., in the single phase regime. So far it has not been established how the domain switching and phase transformation influence each other in the core MPB compositions of piezoelectric alloys. In the present dissertation, we have addressed this issue in an important lead based piezoelectric alloy system (X)BiScO3- (1-X)PbTiO3 (BSPT). In spite of their superior piezoelectric performance, lead based systems have major drawback because of its toxicity and environmental concerns. Several legislations have been passed all over the globe to encourage the development of lead free alternatives. Lead free piezoelectrics belong to three major categories - BaTiO3 (BT) based, Na0.5Bi0.5TiO3 (NBT) based and K0.5Na0.5NbO3 (KNN) based. Among them, NBT based systems have been most widely investigated due to their promising piezoelectric properties –mostly with regard to their large electrostrain response. In this thesis, we have attempted to understand the underlying mechanisms associated with the large piezoelectric response in the lead-based MPB piezoelectric BiScO3-PbTiO3 and also in one of NBT-based lead-free piezoelectric. In the process, we investigated the effect of grain size in influencing the global structure, piezoelectric properties and electrical conduction behaviour of the parent compound NBT. For the first time, in this thesis, we have used rare-earth photoluminescence as a tool to probe the nature of local symmetry in the non-ergodic relaxor ferroelectric state. The thesis comprise of several novel results and ideas which has been systematically detailed in four comprehensive chapters (Chapter 3 to Chapter 6). The thesis comprise of seven chapters. Chapter 1 summarizes some of the basic concepts related to the work presented in this thesis. The experimental techniques and characterizations are discussed in Chapter 2. Chapter 3 deals with a comparative in-situ electric field dependent high energy synchrotron x-ray diffraction (XRD) study on a critical MPB (x=0.3725) and a close by non-MPB (x=0.40) compositions of (X)BiScO3- (1-X)PbTiO3.We show that the rhombohedral ferroelectric-ferroelastic domain reorientation fraction is considerably reduced in the MPB composition as compared to the non-MPB composition. The reduction in the rhombohedral domain reorientation is also accompanied by a corresponding anomalous reduction in the field-induced rhombohedral lattice strain in the MPB along the nonpolar direction. The MPB composition however shows electric-field-induced rhombohedral to tetragonal phase transformation, the fraction of which follows the same hysteretic trend as the lattice strain and domain reorientation fraction. The non-MPB composition, on the other hand does not show field induced phase transformation. We use these results to propose that the field-induced structural transformation is most likely to be the dominant mechanism responsible for the larger macroscopic piezoelectric response in the critical MPB composition of this piezoelectric system. We also found a strong correlation between lattice strain and phase transformation with the field induced domain reorientation in the MPB composition. Although the magnitudes of the changes are very small, we could demonstrate that these phenomena and their coupling occur even in the subcoercive field regime. Chapter 4 to 6 detail the results of the investigation carried out on pure and modified NBT. In Chapter 4, we have reported an extensive study of the effect of grain size on the global structure and piezoelectric response of pure NBT prepared via spark plasma sintering. The grain size was varied in the range 0.2 – 40 µm by changing the annealing temperature. We found that the reported global monoclinic (CC) distortion of NBT collapses for grains size below ~2.5 microns even while it retains its non-ergodic relaxor state. This dramatic change in the global structure on such a large grain size confirms that the characteristic length scale responsible to alter the global structure in this system is mesoscopic in nature. We argue that the perceived difference in the global structure of NBT on size reduction is because of the change in nature of the assemblage of the mesoscopic structural heterogeneity (in-phase and out-of-phase octahedral tilts) inherently present in the system. Further, while we observed a dramatic decrease in the piezoelectric and ferroelectric properties of bulk ceramic with grains in the submicron range, we used an innovative powder poling technique to demonstrate unambiguously that the lack of piezoelectric response is not because of the submicron grains loosing ferroelectric character, but rather because of the inability of the grains to transform to a long ranged rhombohedral ferroelectric state on application of electric (poling) field due to clamping effect and/or increased incoherence of grain boundaries. In Chapter 5, we have demonstrated that the highly efficient nature of the photoluminescence emission of rare earth ions, in conjunction with the sensitivity of the Stark manifolds to the local symmetry, can be utilized to examine the nature of the local structure in the non-ergodic relaxor ferroelectric state of 0.94Na0.5Bi0.5TiO3-0.06BaTiO3. This composition exhibits a cubic like phase on the global structure and there is no unanimity in literature on its structural state on the local length scale. We used Eu and Er as two rare earths to examine the local symmetry in the unpoled and poled states of this system. A series of Eu and Er modified compositions were synthesized as per the nominal formula 0.94Na0.5Bi0.5-x(Eu/Er)xTiO3– 0.06BaTiO3 and a systematic structural, microstructural, piezoelectric and dielectric measurements was carried out. Surprisingly, we found that the number of Stark manifolds in the PL spectra of cubic-like phase is more as compared to that in the field stabilized rhombohedral (R3c) phase. This proves that the local symmetry on the A-site of what appears to be globally more symmetric cubic phase is lower than that in the field stabilized rhombohedral (R3c) phase. Chapter 6 details the results of an extensive investigation to understand the structural mechanism associated with the large electrostrain reported in the lead free system (0.94-x)Na0.5Bi0.5TiO3-0.06BaTiO3-xK0.5Na0.5NbO3 (0.0≤x≤0.025). We show that in the unpoled state, while XRD data suggest cubic like structure, neutron powder diffraction data shows weak superlattice peaks. A systematic structural analysis led us to propose a long period structural modulation of the type √2 x √2 x 16, contradicting the earlier proposal of coexistence of rhombohedral (R3c) and tetragonal (P4bm) phases. We show that the large electrostrain is associated with field induced transformation of the long period modulated structure to rhombohedral (R3c) ferroelectric phase. We also demonstrated that if the field induced R3c phase is partly retained when the field is reduced to zero in the previous cycle, the electrostrain is substantially reduced in the next cycle. The reduced large electrostrain could however be reproduced after heating the specimen above depolarization temperature (~75 oC). Chapter 7 summarizes the essential results of this thesis and also suggests prospects for further research.

碩士
輔仁大學
物理學系
91
Because of the ultrahigh piezoelectric response in (PbMn1/3Nb2/3O3)1-x(PbTiO3)x crystals, especially near the morphotropic phase boundary. It is important to have a better understanding of these origins. The structure transition can be driven by temperature and electric field. We believe that the path of polarization rotation is associated with high-strain performance in PMN-PT system. For technological applications, it is necessary to select the right PT concentrate, temperature and electric field in order to ensure the best performance. Domain structures and dielectric permittivity have been measured as functions of temperature, frequency and electric field on （001）-cut PMN-37%PT, （001）-cut PMN-24%PT, （102）-cut PMN-31%PT and（211）-cut PMN-33%Ptsingle crystals. By using relations of optical indicatrices and extinction, we found the structure and polarization rotation with temperature and electric field changing. The domain structures show a strong hysteresis behavior during processes of increasing and decreasing electric field.

碩士
輔仁大學
物理學系
91
The dielectric constant and polarization-electric field ( P-E) hysteresis loops have been measured as a function of temperature in relaxor ferroelectric single crystals (PbMg1/3Nb2/3O3)1-x(PbTiO3)x , PMN-28%PT[001], PMN-26%PT[110], PMN-31%PT[111], PMN-29%PT[102] . We found that the coervive field Ec and polarization of P-E hysteresis loop increases with increasing PT content. A sharp ferroelectric transition with an abrupt strp-like discontinuity in polarization was observed near 403K for PMN-28%PT[001], 384K for PMN-26%PT[110], 416K for PMN-31%PT[111], 410K for PMN-29%PT[102], respectively. Both thermal hysteresis and discontinous behavior of polarization imply a metastable state at the phase transition temperature, which can only exist theoretically for first-order transition but not second-order transition.

碩士
輔仁大學
物理學系
89
Dielectric Permittivity and domain structures have been measured as a function of temperature in relaxor-based ferroelectric single crystals (PbMg1/3Nb2/3O3)1-x(PbTiO3)x(PMN-x%PT) for x = 0.32 and 0.33 along [001], [110]and[122] orientations, respectively. As temperature increases, PMN-32%PT and PMN-33%PT undergo successive phase transitions: rhombohedral phase ® coexistence of rhombohedral and tetragonal phases ® tetragonal phase ® coexistence of tetragonal and cubic phases ® cubic phase. A relaxation mechanism which is responsible for the so-called diffuse transition, crossovers a wide-temperature region of ~340-400 K, and may result from partial microdomains conversion from rhombohedral to the tetragonal phase. Extra peak dielectric anomalies were observed in each crystal, possibly due to the percolating polar cluster induced by an external electric field. A field-induced tetragonal symmetry was evidenced and coexists with rhombohedral symmetry in the low-temperature region. In addition, field-induce tetragonal phase along the external field was observed.

碩士
國立成功大學
電機工程學系碩博士班
96
0.7Pb(Fe2/3W1/3)O3(PFW)-0.3PbTiO3(PT) is one of the classic relaxors with little diffuse-phase-transition(DPT) in normal temperature and lots of dielectric loss caused by space charge appearance. In present work, the 0.7PFW-0.3PT relaxor is synthesized with the conventional solid solution. To decrease the dielectric loss and make the dielectric diffusion property increases we doped the dopant La2O3 for the 0.7PFW-0.3PT. Although, the broader peak dielectric constant is obtained as doping La2O3, the curie point moves to lower temperature. According to the experimental results, the very lower dielectric loss is observed as doping 5at% La2O3. The smoothest dielectric constant in the normal temperature range is obtained between x=0.3 to 0.4 in (1-x)PFW-xPT doped the 5at% dopant La2O3. To discuss dielectric loss and DPT in different ratio Pb(0.95)La0.05(Fe2/3W1/3)0.65Ti0.35O3 prepared by ball-milled method in two steps and direct method also in this present work .

碩士
國立成功大學
電機工程學系碩博士班
94
Pb(Fe2/3W1/3)O3(PFW) is one of the classic relaxors, with the phase transition temperature of -90℃. Since the phase transition temperature of the PbTiO3-PT is 490℃, the phase transition temperature can be adjusted to higher temperature in need by increasing the x ratio for the (1-x)PFW-xPT solid solution. In present work, the (1-x)PFW-xPT relaxor system is synthesized with the conventional solid solution. The dielectric loss decreases and the dielectric diffusion property increases as doping the dopant MnO for the (1-x)PFW-xPT. Although, the broader peak dielectric constant is obtained as doping MnO, the improvement is not sufficient for the application of capacitor. A great improvement on the temperature dependence of the dielectric constant has been done by using the temperature-compensation method, where the two-layer-structure capacitor is stacked with two heterogeneous dielectric materials of 0.8PFW-0.2PT-0.15w%MnO and 0.7PFW-0.3PT-0.15w%MnO ceramics. According to the experimental results, the very lower dielectric loss is observed as doping 0.15w% MnO. The smoothest dielectric constant in the temperature range between -10℃ and 40℃ has been accomplished for the two-layer-structure capacitor with the weight ratio of 2:1 the0.8PFW-0.2PT-0.15w%MnO and the 0.7PFW-0.3PT-0.15w%MnO.

Perovskite materials have been widely embedded in many consumer and industrial electronics, both for capacitor applications in the case of dielectric materials, and for actuator, transducer and sensor applications in the case of piezoelectric materials. Functional devices used in high temperature environments, such as deep oil well instrumentation, geothermal exploration, and devices for aerospace applications require the persistence of materials’ properties at high temperatures. In this paper, high potential capacitor and piezoelectric ceramics for high temperature applications are presented. High dielectric constant (K) materials based on 0.8BaTiO3 – 0.2Bi(Zn1/2Ti1/2)O3 solid solutions have been shown to have superior properties for high temperature capacitor applications. Studies of the temperature dependence of the dielectric properties have shown that the composition with Ba vacancies exhibits a high relative permittivity (εr > 1150) and a low dielectric loss (tan δ < 0.05) that persist up to a temperature of 460 °C. This composition also shows a high resistivity in excess of 7.0 × 1010 Ω-cm which remains unchanged up to a temperature of 270 °C as well as a large RC time constant (RC > 20 s). In the case of high temperature piezoelectric ceramics, solid solutions of PbTiO3 – BiScO3 – Bi(M1/2Ti1/2)O3 ternary systems were studied, where M is Mg and Zn. The ratio of BiScO3 to Bi(M1/2Ti1/2)O3 was kept at 1:1, while the concentration of PbTiO3 was varied. X-ray diffraction patterns showed that tetragonal symmetry was observed in compositions which contain a high concentration of PbTiO3 (> 60 mol%). Evidence of a morphotropic phase boundary (MPB) was observed with compositions containing PbTiO3 in the range of 52–56 mol%. At 70 mol% PbTiO3 compositions, high Curie temperatures (TC) of 490 °C and 533 °C were observed for compositions containing Mg and Zn, respectively.