obtained the polar phase transition to non-polar phase due to Li-modiﬁed at A-site of BNKT-Ta. 11) However, the Li + ions promotion the tetragonal phase developed from pseudocubic phase in BNKT-Sn. 12,23) In other word, the phase transition combination with distorted structure ob- tained via BLTO-modi ﬁ ed BNKTBA ceramics.
Perovskite-based materials are in the focus of research not only because of their ex- cellent physical properties, but also because their relatively simple structure facilitates the understanding of structure-property relationships, which is crucial for developing novel materials with improved qualities. Recent research in the field of ferroelectric and piezoelectric materials is concerned with the development of eco-friendly lead-free materials. To achieve this goal, it is important to understand the fundamental correla- tion between the ‘Structure’ and the ‘Property’. In this work, the primary focus has been to elucidate the structural changes occurring as a function of doping in three dif- ferent systems: (1) BiScO 3 −PbTiO 3 (BS-PT), a recently developed system which has already attracted much interest because of its superior physical properties near the mor- photropic phase boundary (MPB); (2) BiScO 3 −BaTiO 3 (BS-BT), which can be consid- ered as a lead-free analogue of the BS-PT family and lastly, (3) Na 0.5 Bi 0.5 TiO 3 −BaTiO 3 (NBT-BT), which is a well-known lead-free material at the NBT-rich side of the phase diagram.
non-linear dielectric, ferroelectric, and piezoelectric responses 13,14 and was more recently reapplied. 15,16 The intrinsic contribution is a result of the atomic displacements of the unit cell under an applied field, whilst the extrinsic contribution is a result of non-180 domain wall motion 17 and is generally associated with irreversible and lossy proc- esses and can greatly affect the electromechanical response. Therefore, as the intrinsic and extrinsic contributions vary with composition and temperature, 18 Rayleigh analysis is an effective method of analysing new materials. Piezoelectricceramics are often characterised from electrical impedance at low voltage (0.5–1 V) frequency sweeps in conjunction with the sample geometry and density 19 while transducers and actuators are typically driven at much higher excitation levels (1–2 kV/mm). 20 This technique therefore allows the possibility of simulated studies of real applications (assum- ing that the ceramics will not be driven by bipolar switching electric-fields). The technique has been applied to BaTiO 3 ,
Piezoelectric materials are expected to acquire a market of around $ 95 billion by 2017. Due to toxicity of Lead Zirconium Titanate [PZT] ceramics, its usage will end by 2017. So the recent research is concentrated on developing lead free piezo ceramics [1-7]. With this regard, two classes of lead free piezoelectric materials have drawn more attention, viz. bismuth layer structured ferroelectrics and perovskite structured ferroelectrics. Barium sodium titanate [BNT] based ceramics show large remnant polarization (38μC/cm 2 ) but with a large coercive field (73kV/cm)  and a phase transition at 200 C from ferroelectric to anti ferroelectric. KNN is good compared to BNT due to its high Curie temperature. But achieving fully dense sodium– potassium based ceramics is difficult from normal sintering.Thus KNN powder has shown certain promising result which makes it a novel alternative for
ing the formation of the pyrochore phase and they will be detrimental to the physical properties of lead based ferroelectricceramics . Therefore, in this work, we combined the conventional solid-state reaction method and the B-site Oxide mixing technique (BO) for fabricate ceramic samples. Firstly, the mixture of (Zn 0.125 Mn 0.075 )Nb 0.4 [(Zr 0.48 Ti 0.52 ) 2.4 ]O 6 (BO) were prepared by reactions of ZnO, MnO 2 , Nb 2 O 5 , ZrO 2 and TiO 2
and Na doped PBN single crystals studied by Xu et al. . Low Qm piezoelectricceramics are suitable for wide band ultrasonic transducer applications. The piezoelectric effect of ferroelectricceramics has vast potential as electromechanical transducers. The piezoelectric transducers are limited to device involving only very small mechanical displacements and small amounts of electrical charge per cycle. In this paper we briefly studied the structure, dielectric and piezoelectric properties of ceramics by solid state reaction method.
into account the relationships between the primary material coefficients, a simple classical mechanics model has been proposed. 11 The model is based on the simplest structural motif necessary to provide piezoelectric behavior: a 3 atom dipole defined by an effective ionic charge and asymmetry in the strength of the interatomic bonds. Applying this Equiv- alent Dipole Model to the property data for any piezoelectric material, both ferroelectric and non-ferroelectric, provides an evaluation of the effective charge and bond strengths, which can be used as simple parameters to describe and compare the origin of the piezoelectric effect in that material.
axis is investigated from first principles. We show that the calculated ideal tensile strength is 6.85 GPa and that the superlattice under the loading of uniaxial tensile stress becomes soft along the nonpolar axes. We also find that the appropriately applied uniaxial tensile stress can signifi- cantly enhance the piezoelectricity for the superlattice, with piezoelectric coefficient d 33 increasing from the
increased from 44 pC/N for KBT to a maximum of 130 pC/N at x = 0.1, decreasing to ~ 100 pC/N for x = 0.2 and then dropping sharply at x > 0.2, Figure 8. Hence the optimum ferroelectric and piezoelectric properties in KBT-BZT occur around the changeover in phase content from tetragonal to mixed phase (tetragonal and pseudocubic) at x = 0.1. A future detailed crystallographic study would clarify the symmetry of the ferroelectric phase(s) in this region.
further attrition milled and dried as mentioned above. The attrition milled powder was mixed with poly(vinyl alcohol) equal to 0.5 wt% of the attrition milled powder, dried, pulverized by using an agate pestle and mortar, and sieved through a 250 micron mesh. ~0.3 g batches of powder were uniaxially pressed into discs with diameter of 10 mm at 125 MPa to form green body pellets. These compacts were sintered 2 h between 940 to 1020 ºC after burning out the binder at 550 ºC. Sintering temperatures and relative densities of the ceramics are shown in Table 3. To evaluate the electric, dielectric, and piezoelectric properties of the samples, silver paste electrodes were applied to the sintered pellets, and then fired 2h at 500 ºC.
grains, as indicated by the arrow in Figure 3(b). An an- gular grain with a flat surface is typically observed in the abnormal grain growth in the presence of the liquid phase. Therefore, it was considered that densification of the Li and Sb co-doped KNN ceramics might be explained by the liquid-phase sintering. This may be attributed to the low melting temperature of Li compounds that appears to promote the formation of a liquid phase during sintering. However, it was very difficult to find liquid phase, im- plying that the liquid phase formed during the sintering could be a transient liquid phase, with a high solubility in the KNN ceramics that led to its eventual disappearance with sintering time. Figures 3(c) and 3(d) shows the KNN ceramics sintered at 1100˚C and 1120˚C; enlarged grains can be observed showing an abnormal grain growth (AGG). Their relative density was found to be much less as compared to the ceramics sintered at 1080˚C. It is generally agreed that AGG is caused by the existence of a liquid phase. Chun et al.  found that extensive AGG occurred on the surface of a sintered Ba- TiO 3 specimen and concluded that the BaO evaporation
order parameter φ, for example the angle of rotation of the octahedra. Then, the free energy F contains additional terms with even powers of φ, possible FE-tilt coupling terms containing both P and φ, and the coupling between φ and stress σ is exactly of the form (8) of the electrostrictive coupling, ∝ σφ 2 [29,30]. As a consequence, if the coupling between FE and tilt modes is weak, with two transitions well separated in temperature, the compliance will undergo two well separated softenings at the two transitions, and the previous treatment is still valid at the FE transition. It is impossible to distinguish which is the FE transition from the elastic measurement alone, but it is very easy from the dielectric susceptibility. In fact, the latter presents a huge peak of Curie-Weiss type at the FE transition, but only a small step at the tilt transition, if this occurs within the ferroelectric phase. This is due to the coupling between polarization and tilting, which, for symmetry reasons, to the lowest order is biquadratic , k 2 P 2 φ 2 , and simply renormalises the α 2 P 2 term in the free energy (11) as 1 2 α + kφ 2 P 2 and the susceptibility in the FE phase, Eq. (13), from χ = 1/ ( 2α ) to 1/2 α + kφ 2 . Below the tilt transition transition temperature T T , φ passes from 0 to φ 0 ( T ) producing a step in χ,which is positive for
evident as x increases, all compositions, however, still show the features of long-range polar order. It is also worth noting that the aforementioned modes 1 and 2 are present at all tem- peratures. Hence, based on both permittivity measurements and Raman spectroscopy analysis, all ceramics studied exhibit dielectric anomalies associated with structural phase transitions, and their ferroelectric nature is corroborated by the presence of a Fano-type resonant dip in their Raman
compositionally driven phase transition is nearly independent of temperature, PZT has been widely applied to many applications. T and R phases have six spontaneous polariza- tion directions along h001i and eight along h111i, respec- tively. Therefore, at the MPB, there exist many possible polarization directions and hence high piezoelectric proper- ties are generated. In addition, Noheda et al. 8,9 reported a monoclinic (M ) phase between the T and R phase in PZT in 1999. The M phase has 24 possible polarization directions which enhance the electromechanical properties. The prop- erties of commercial PZTs are controlled by dopants which are broadly categorized as soft PZT (donor doped) and hard PZT (acceptor doped). 10–14 These features have made PZTs the most widely used piezoelectrics to date.
is indicated by the dashed line in part (b) of Figure 4. 1. From this figure it is also evident that the position of the reflection associated with the undoped phase remains virtually unchanged, however its intensity decreases with the increasing x. Basically this observation shows that at low dopant levels homogenisation is more difficult to achieve. Conversely, the shoulder that start appearing in KBBNZ x=0.05 shifts slightly towards lower angles with increasing x, making the peak splitting clear. This suggests there are some difficulties in the simultaneous incorporation of Ba +2 , Bi +3 , Zn +2 and Nb +5 into the KN lattice, using the processing conditions established in Chapter 3 for undoped KN. The calcined powders were uniaxially pressed into pellets under 1 ton. Then, green bodies were fired in air for 12 hours at temperatures ranging from 1070 to 1100 °C, using a controlled heating rate of 3 °C/min. Room-temperature X-ray diffraction (XRD) data for KBBNZ ceramics are shown in Figure 4. 2.
mapping (Fig. 2d-k). The EDS elemental maps of polished BF-BT-0.05BZN samples are shown in Fig. 2(d-k). The Ba and Ti signals are weaker in the brighter regions of the SEM image, associated with the grain cores (Fig. 2d and e). Conversely, Bi and Fe exhibit a slightly increased intensity in the brighter areas (Fig. 2f, g). These results indicate that the observed core-shell microstructure in BF-BT- xBZN are associated with the micro-segregation of Ba and Ti into the shell, while Bi and Fe are concentrated in the core regions. 41-47. Murakami et al. investigated the role of composition and quenching on core-shell formation in BiMg 1/3 Nb 2/3 O 3 doped BF-BT ceramics. 41,42 They concluded that
the ferroelectric rhombohedral polymorph. It is worth the note that the aforementioned modes 1 and 2 are present at all temperatures. Hence, based on both permittivity measurements and Raman spectroscopy analysis all ceramics studied exhibit dielectric anomalies associated with structural phase transitions and their ferroelectric nature is corroborated by the presence of a sharp mixed mode (at ~290 cm -1 ) and by a Fano-type resonant dip in their Raman spectra. Basically, all studied ceramics are ferroelectric in a wide temperature range.
voltage constant geff. The Cymbal transducer exhibited a higher deff · geff than that of other transducer structures such as multilayer stacks and bimorphs. The actual piezoelectric coefficient of the Cymbal transducer was amplified several times because the presence of a cavity enabled the metal end-caps to serve as a mechanical transformer, transforming and amplifying a portion of the incident axial stress in the radial stresses of an opposite sign . Recently, the authors  investigated the effect of dimensional size on the output electrical characteristics of uncapped PZT piezoelectricceramics by using drop weight impact techniques. In this paper, the authors using drop weight impact techniques to study the output electrical characteristics of PZT piezoelectricceramics Cymbal transducer, and the effects of geometric parameters of metal end-cap on the output electrical characteristics are study also.
According to Figure 11, the curve peak with increase- ing frequency, has not an outstanding displacement along the vertical axis and this represents which the BMT-BT lead free ceramic is not ferroelectric relaxor. Table 2 listed the electrical parameters of the BMT-MOM and BMT-ACM ceramics that sintered at different tempera- tures. According to Table 2, the grain size has strong effects on dielectric properties and polarization of piezo- electric materials . On the other hand, all electrical coefficients at optimum temperatures (1200˚C) were in- creased.