Relaxor Composition Research Articles

Achieving large strain and low hysteresis in BiFeO3-BaTiO3-based piezoelectric ceramics

The high strain hysteresis has impeded lead-free piezoelectric ceramics to replace lead zirconate titanate ceramics applied in actuators. In this study, we report a significant advancement with the synthesis of a novel BiFeO3-BaTiO3-(Ba0.6Sr0.4)TiO3 (BF-BT-BST) system. The optimal composition has demonstrated a remarkable strain of 0.42 % coupled with a notably low hysteresis of 21 %. It is found that the incorporation of BST into BF-BT facilitates the transition from the rhombohedral phase to the pseudo-cubic phase, which in turn significantly enhances the relaxor ferroelectric characteristics of the ceramic. Through adjusting the composition proportion of BST, a unique ferroelectric domain structure is established for the BF-BT-0.04BST ceramic, where polar nanoregions (PNRs) are surrounded by ferroelectric macrodomains. The domain structure enables the ceramic to have the ability to respond the external electric field quickly compared to the PNRs for typical relaxor composition, thereby leading to large strain and low hysteresis simultaneously. Hence, it is inferred that the ferroelectric macrodomains simplify the response process of the PNRs under electric field. This study provides an efficient strategy to break through the bottleneck of large strain hysteresis for BF-BT ceramic, and gives a deep comprehension for the improvement of the strain characteristics.

Strain properties of (1-x)Bi0.5Na0.4K0.1TiO3-xBi(Mg2/3Ta1/3)O3 electroceramics

A ternary solid solution of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–Bi(Mg2/3Ta1/3)O3 (BNKT-xBMT) lead-free electroceramics was synthesized by a solid-state reactive sintering technique. The electrostrain, dielectric, and ferroelectric properties as well as the impedance characteristics and the microstructure were systematically assessed. With the increase of BMT, the BNKT-xBMT ceramics gradually transformed from non-ergodic relaxor phase to ergodic relaxor phase, manifested as the ferroelectric-to-relaxor temperature (TF-R) shifts towards below room temperature. Additionally, the ferroelectric hysteresis curves became pinched, and the strain curve changed from butterfly-shaped into sprout-shaped. At the ergodic relaxor composition of x = 0.04, a large electrostrain value (S = 0.4%; under an electric field of 60 kV/cm, d33* = 632 pm/V) was achieved, which is mainly attributed to the electric-field-induced transition from the ergodic relaxor phase to the ferroelectric phase.

Nanoscale compositional segregation and suppression of polar coupling in a relaxor ferroelectric

A number of relaxor ferroelectric ceramics have been demonstrated to possess a near stable value of relative permittivity over very wide temperature ranges. This cannot be explained by conventional theories of relaxors. One such system is based on the perovskite solid solution series: (1-x) (Ba0.8Ca0.2)TiO3-xBi(Mg0.5Ti0.5)O3, giving stable relative permittivity from 150 to 500 °C. We show by scanning transmission electron microscopy and electron energy loss spectroscopic elemental mapping that nanoscale compositional segregation occurs in the temperature stable relaxor composition (x = 0.55), with Ba/Ti clusters some 2–4 nm in extent, separated by Bi-rich regions of comparable size. This nanomosaic structure is consistent with phase separation into a ferroelectrically active BaTiO3 – type phase (Ba/Ti rich) and a weakly polar Bi/(Mg) rich perovskite solid solution. The possibility that nanophase segregation is the cause of weak dipole coupling and suppression of the dielectric relaxation peak is considered.

Structural and Dielectric Properties of Sn Doped Barium Magnesuim Zirconium Titanate Perovskite Ceramics

Perovskite type ceramics (Ba0.9Mg0.1)(SnxZr0.4-xTi0.6)O3 (with x = 0.01, 0.02, 0.03 and 0.04) relaxor composition prepared through solid state reaction route and calcinated at temperature is 1150°C for 5 hrs with intermediate mixing. The room temperature XRD study suggests that all the samples have the single phase cubic symmetry with space group pm 3 m. The pellets were sintered at 1500°C for 4 hrs. Scanning Electron Microscope (SEM) observations revealed enhanced micro structural uniformity and retarded grain growth with decreasing Sn content. The dielectric measurements at constant frequency show that dielectric constant increases with Sn content. Loss factor and dielectric constant decreased with increasing frequency but at very high frequencies it was independent.

Fabrication of Relaxer-Based Piezoelectric Energy Harvesters Using a Sacrificial Poly-Si Seeding Layer

The effect of a polycrystalline silicon (poly-Si) seeding layer on the properties of relaxor Pb(Zr0.53,Ti0.47)O3–Pb(Zn1/3,Nb2/3)O3 (PZT–PZN) thin films and energy-harvesting cantilevers was studied. We deposited thin films of the relaxor on two substrates, with and without a poly-Si seeding layer. The seeding layer, which also served as a sacrificial layer to facilitate cantilever release, was found to improve morphology, phase purity, crystal orientation, and electrical properties. We attributed these results to reduction of the number of nucleation sites and, therefore, to an increase in relaxor film grain size. The areal power density of the wet-based released harvester was measured. The power density output of the energy harvester with this relaxor composition and the poly-Si seeding layer was 325 μW/cm2.

Spontaneous long and short-range ferroelectric ordering in Pb0.55La0.30TiO3 ceramics

In this work, we investigated the temperature dependence of short and long-range ferroelectric ordering in Pb0.55La0.30TiO3 relaxor composition. High-resolution x-ray powder diffraction measurements revealed a clear spontaneous macroscopic cubic-to-tetragonal phase transition in the PLT relaxor sample at ∼60 K below the maximum of the dielectric constant peak (Tm). Indeed, the x-ray diffraction (XRD) data showed that at 300 K (above Tm but below the Burns temperature, TB) the long-range order structure corresponds to a macroscopic cubic symmetry, space group number 221 (Pm-3m), whereas the data collected at 20 K revealed a macroscopic tetragonal symmetry, space group number 99 (P4mm) with c/a=1.0078, that is comparable to that of a normal ferroelectric. These results show that for samples with tetragonal composition, the long-range ferroelectric order may be recovered spontaneously at cryogenics temperatures, in contrast to ferroelectric samples with rhombohedral symmetry. On the other hand, x-ray absorption spectroscopy investigations intriguingly revealed the existence of local tetragonal disorder around Ti atoms for temperatures far below Tm and above TB, for which the sample presents macroscopic tetragonal and cubic symmetries, respectively.

Low‐frequency 1/f noise in relaxor ferroelectric PMN–PZT

AbstractThe dielectric properties of relaxor ferroelectric ceramics (1 – x)PbMg1/3Nb2/3O3–(x)PbZr0.53Ti0.47O3(PMN–PZT) have been studied at various frequencies in the temperature range of the diffuse phase transition. Dispersion of the complex dielectric permittivity ε * characteristic for relaxors was revealed in the vicinity of the ε * maximum temperature Tm. It has been determined that low‐frequency 1/f noise in the studied system is mainly caused by the polarization relaxation in local polar regions and the spectral density of the noise depends on the relaxor composition and temperature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Low-frequency dielectric relaxation (1/f noise) in relaxors of the (1 − x)PMN-(x)PZT system

The dielectric properties of relaxor ferroelectric ceramics (1 − x)PbMg1/3Nb2/3O3-(x)PbZr0.53Ti0.47O3 (PMN-PZT) have been studied at frequencies from 40 Hz to 1 MHz in the temperature range of the diffuse phase transition. It is established that the dielectric relaxation generates 1/f noise, whose spectral density depends on the relaxor composition and temperature.

Ferroelectric behavior in nominally relaxor lead lanthanum zirconate titanate thin films prepared by chemical solution deposition on copper foil

We demonstrate that (Pb0.9La0.1)(Zr0.65Ti0.35)0.975O3 (PLZT) (10∕65∕35) thin films that have a nominally relaxor composition and that are deposited by chemical solution deposition onto copper foil show polarization hysteresis. Ferroelectric domain switching and a shift in Curie temperature are also observed. This is in contrast to the non-hysteretic behavior of films with identical composition prepared on Pt∕SiO2∕Si substrates. This suggests that the mismatch in coefficient of thermal expansion between PLZT and copper induces a compressive strain in the PLZT during cooling after high temperature crystallization under low pO2, and causes an out-of-plane polarization.

Study of disorder in a tetragonal tungsten bronze ferroelectric relaxor: a structural approach

Electron diffraction analysis, nuclear magnetic resonance measurements, structure determinations and refinements were performed on two ferroelectric lead-containing ceramics (classical and relaxor), with tetragonal tungsten bronze structure, in order to investigate the origin of the relaxor behaviour in such compounds. In both compounds the lead atoms are found to be off-centred in the CN (coordination number) 15 (A2) site. The main difference between the two compositions is the proportion of lead in this site: in the relaxor composition, theA2 site is at least half occupied by lead atoms. Disorder in the repartition of lead and potassium atoms in theA1 (CN 12) andA2 sites was also studiedviacombinatorial calculations to correlate the evolution of the relaxor behaviour in the Pb5Ta10O30–Li10Ta10O30–K10Ta10O30ternary system with composition. The combinatorial study demonstrated that the relaxor behaviour is enhanced by the disorder in cationic repartition.

Polarization anomalies in a relaxor ferroelectric

With a strontium barium niobate crystal used as an example, it is experimentally demonstrated that relaxor ferroelectrics exhibit pronounced polarization anomalies, which manifest themselves in the difference between the trajectories of the dielectric hysteresis observed in several repeated cycles of a varying external electric field. These anomalies originate from the nonuniformity of the relaxor composition, local symmetry lowering, local internal electric field, and a wide distribution of potential barriers in energy for the polarized regions. The anomalies can be observed only in slowly varying (quasistatic) or constant electric fields.

Fracture of ferroelectric and relaxor electro-ceramics: influence of electric field

Crack growth is studied in a ferroelectric and a relaxor composition of lead lanthanum zirconate titanate (PLZT) ceramic using Vicker’s indentations with electric field. The polarized ferroelectric composition displays excess crack growth perpendicular to the polarization direction. This excess crack growth is increased by an electric field in the polarization direction. The relaxor composition does not display this excess crack growth. Results suggest that the excess crack growth perpendicular to the polarization is the result of intergranular residual stress.

A polarized Raman study of the relaxor and ferroelectric states of La-modified lead zirconate titanate ceramics

Lanthanum modified lead zirconate titanate ceramics with La/Zr/Ti ratios of 6/40/60, 12/40/60, 5/65/35, and 9/65/35 have been studied by polarized Raman scattering. In the two former (tetragonal-type) compositions, selection rules were rather well defined and allowed an assignment of the Raman lines at lower temperature. These selection rules disappeared for 6/40/60 but remained for 12/40/60 even at higher temperatures. The behavior of the two latter (rhombohedral-type compositions) was quite different. No assignment of lines could be done. In addition, the spectra recorded in parallel and crossed polarizations were almost identical for 5/65/35 regardless of temperature. A very smeared paraelectric to ferroelectric transition was evidenced by Raman intensity measurements for this composition. On the contrary, selection rules were always present for the relaxor composition 9/65/35 which were similar to those for 12/40/60 and 6/40/60. This suggests that both tetragonal and rhombohedral-type local polar order is present for 9/65/35. The spectra of the field induced ferroelectric phase for 9/65/35 revealed no selection rules, similar to 5/65/35. This is attributed to the onset of only medium range ferroelectric order. Finally, Raman spectra recorded on powders of every composition did not reveal any selection rules, suggesting that intergranular effects might play a significant role in the behavior of these materials.