Aurivillius Phase Ceramics Research Articles

Electrical properties of Bi2.99(Li0.5Sm0.5)0.01Ti1-x(Mn1/3Ta2/3)xNbO9 high-temperature piezoelectric ceramics via oxygen vacancy defects tailoring

Tribismuth titanium niobium oxide (B3TiNbO9, BTNO) is one of the Aurivillius phases with the highest Curie temperature (Tc), but its piezoelectric coefficient (d33) is poor. When x = 0.045, high-temperature piezoelectric ceramics with d33 of 11.9 pC/N and Tc of 916.7 °C were prepared by (Mn1/3Ta2/3)(4+ω)+ modification of Ti4+ at B-site of Bi2.99(Li0.5Sm0.5)0.01Ti1-x(Mn1/3Ta2/3)xNbO9. The substitution will aggravate the distortion of BO6 octahedron due to the displacement of oxygen ions. The existence of Mn3+ in the dopant will act as an oxygen vacancy trap and then increase the resistivity. As a result, BTNO ceramics have enhanced piezoelectric properties as well as temperature and cycle stability. This work provides a theoretical basis for better high-temperature piezoelectric properties of A/B co-doped Aurivillius phase ceramics in the future.

Room-temperature multiferroic behaviour in Co/Fe co-substituted layer-structured Aurivillius phase ceramics

Room-temperature single-phase multiferroic materials have attracted the considerable attention of may scientists due to their technological applications in the next-generation electronic devices. Here, we report the structural evolution and its relationship with the ferroelectric and magnetic properties of Aurivillius Bi3.25Sm0.75Ti(3-x) (Fe,Co)xO12 (BSmT:FCx); for (0≤x ≤ 0.4) ceramics to elucidate the room-temperature multiferroics induced by Fe/Co co-substitution. The XRD analysis and structural refinements reveal that incorporating of Co, and Fe ions into Ti sites of BSmT host lattices gives rise to a single orthorhombic phase with no evidence of secondary phases. The X-ray photoelectron spectroscopy (XPS) spectra indicate the existence of oxygen vacancies in the investigated samples. Pure BiT samples exhibit diamagnetic behavior, while BSmT:FCx; for (0≤x ≤ 0.4) exhibits ferromagnetic behavior at room temperature. As a result, the sample with x = 0.4 displayed the highest remnant and saturation magnetization values. It is believed that the occurrence of magnetism causes by the magnetic double exchange interaction between the non-equivalent magnetic ions and oxygen. The reversible polarization induced by an electric field indicates the ferroelectric character of the ceramics at room temperature. The co-substituting samples show unsaturated P-E hysteresis loops, which could be caused by the domain pinning induced by the accumulation of oxygen vacancies near the domain boundaries. We expect these compounds are promising for developing electronic devices for future applications.

Microstructure and Electrical Properties of Lanthanides-doped CaBi2Nb2O9 Ceramics

Calcium bismuth niobate (CaBi2Nb2O9, CBN) is a promising candidate for high-temperature applications in aerospace, shipping, and nuclear industries, owing to its ultra-high Curie temperature (TC∼x223C 940 °C). Lanthanide ions modified CBN based ceramics were prepared by a conventional solid-state sintering route. The crystal structure, microstructure, and high-temperature electrical properties of CBN ceramics doped by different lanthanide dopants (La, Ce, Nd, Sm, Dy, Er, Yb) were studied and the underlying mechanism was also discussed. Among these doping ions, Ce3+/Ce4+ doping CBN ceramics exhibits anomalous electrical properties. Impedance analysis was introduced to clarify the difference in electrical properties of lanthanide-doped CBN ceramics at high temperatures. As a result, the anomalous electrical properties are attributed to the extrinsic oxygen vacancies induced by the Ce doping. These results could assist to tailor the electrical properties of Aurivillius phase ceramics with lanthanide modifications.

Multi elements substituted Aurivillius phase relaxor ferroelectrics using high entropy design concept

The concept of high entropy ceramics opens up the possibility to optimise the properties of relaxor ferroelectrics with Aurivilius phase structures. In this paper, two new multi-element substituted Aurivillius phase ceramics, (Ca0.25Sr0.25Ba0.25Pb0.25)Bi2Nb2O9 and (Ca0.2Sr0.2Ba0.2Pb0.2Nd0.1Na0.1)Bi2Nb2O9 are prepared. Both ceramics are single phase, exhibiting orthorhombic symmetry with space group A21am at room temperature. The frequency dependence of the temperature of the dielectric permittivity peak, Tm, shows relaxor behaviour for both ceramics. Multi-domain configurations, including long range ordered ferroelectric domains and nano domains, were observed using piezoresponse force microscopy (PFM). Under an applied DC field, the nano domains irreversibly transformed to micro-meter sized domains, which is consistent with the Vogel-Fulcher Law fitted results that show that the freezing temperatures of the two ceramics are above room temperature. Their improved piezoelectric constant is attributed to their low coercive fields, which are related to the multi domain configurations in the Aurivillius phase relaxor ferroelectrics.

Room-temperature multiferroic behavior in layer-structured Aurivillius phase ceramics

Multiferroics that simultaneously exhibit ferroelectricity and ferromagnetism have recently attracted great attention due to their potential application in next generation electronic devices. However, only a few single-phase multiferroic materials exhibit ferroelectric and ferromagnetic orders at room temperature. Recently, some bismuth layer-structured Aurivillius compounds were reported as multiferroics at room temperature, but the origin of their magnetic property is still under debate because the net magnetization may originate from the presence of secondary phases that are not easily detected by laboratory XRD diffractometers. Here, textured Aurivillius phase Bi5.25La0.75FeCoTi3O18 ceramics were prepared by Spark Plasma Sintering. The ferromagnetic character of the ceramics was indicated by the magnetic field-induced reversible intensity changes of a certain set of crystalline planes belonging to the Aurivillius phase, as measured by in situ neutron diffraction under the applied magnetic field. The first principles calculations indicate that the ferromagnetism originates from double exchange interactions Fe3+–O–Fe3+, Co3+–O–Co3+, and Fe3+–O–Co3+ in the ferro-toroidal main phase. The magnetic-controlled ferroelectric domain switching was observed by piezoelectric force microscopy at room temperature. The prepared Aurivillius phase ceramics, with Co/Fe contributing to magnetization and polarization at the same time, can be considered an intrinsic room-temperature multiferroic.

Evolution of microstructure and electrical properties of Aurivillius phase (CaBi4Ti4O15)1-x(Bi4Ti3O12)x ceramics

(CaBi4Ti4O15)1-x(Bi4Ti3O12)x (CBT-xBIT) Aurivillius phase ceramics were synthesized by the conventional solid reaction method. The evolution of the structure and the electrical properties of CBT-xBIT ceramics were systematically investigated. Due to the enhanced spontaneous polarization induced by internal stresses on the Bi2O2 layers in the CBT-xBIT structure, the optimal piezoelectric coefficient (d33 ~ 13 pC/N) was obtained in the ceramics with x = 0.3 while exhibiting a relatively good thermal stability in the temperature range of 20–700 °C. The dc resistivity (ρdc) of the CBT-xBIT ceramics exhibited a higher value (≥ 109 Ω cm) at room temperature, and the tan δ value of CBT-xBIT (x= 0, 0.1 and 0.3) within the temperature range of 20–500 °C maintained stability as a result of the domain structure and point defect concentration in the ceramics. In addition, a distinctive double dielectric peak anomaly was observed in the εr-T curves of the CBT-xBIT (x= 0.3, 0.5 and 0.7) ceramics, and it plays a remarkable role in the thermal stability of the piezoelectricity of CBT-xBIT ceramics. As a result, such research can benefit high temperature practical piezoelectric devices.

Crystal structure and electrical properties of (Li, Ce, Nd)-multidoped CaBi2Nb2O9 high temperature ceramics

(Li, Ce, and Nd)-multidoped CaBi2Nb2O9 (CBN) Aurivillius phase ceramics were prepared via a conventional solid-state sintering route. The crystal structure including bond lengths and bond angles, microstructure, dielectric constant, DC resistivity, and piezoelectric properties were systematically investigated. Rietveld-refinements of X-ray results indicated that small quantity of (Li, Ce, Nd) doping (< 2.5mol%) increases orthorhombic distortion, because of the smaller ionic radii of doping ions. However, orthorhombic distortion obviously decreased with increasing (Li, Ce, Nd) doping concentration from 5 to 25mol%. The replacement of asymmetric A-site Bi3+ with 6s2 lone pair electrons by symmetric Li+, Ce3+ and Nd3+ ions decreased the orthorhombic distortion. The morphologies and electrical properties of sintered ceramics were tailored by the introducing (Li, Ce, Nd) multi-dopants. The improvement of piezoelectric properties of modified-CBN ceramics were attributed to decreasing grain sizes and morphotropic phase boundary (MPB). Ca0.85(Li0.5Ce0.25Nd0.25)0.15Bi2Nb2O9 (CBNLCN-15) ceramics had optimum properties, and d33 and Tc values were found to be ~ 13.1 pC/N and ~ 900°C, respectively.

Room temperature magnetoelectric coupling in intrinsic multiferroic Aurivillius phase textured ceramics.

Spark plasma sintering was employed in order to obtain textured Aurivillius phase ceramics that simultaneously exhibit ferroelectric and ferromagnetic properties at room temperature. The sintered multiferroics are layer-structured, nearly single-phase materials. Although a small amount of the secondary phase consisting of magnetic Co and Fe was detected by SEM/EDX, a majority of the observed ferromagnetic behaviour was attributed to the Aurivillius phase Bi4.25La0.75Ti3Fe0.5Co0.5O15 based on the observed magnetic anisotropy. The ferroelectric switching was demonstrated to exist in the Aurivillius phase ceramics by measuring the current peaks upon electric field reversal. Piezoresponse force microscopy at room temperature revelaed substantial changes of the ferroelectric domain structure when the Aurivillius phase material is subjected to an external magnetic field.

Structural, magnetic and dielectric properties of the Aurivillius phase Bi6Fe2−xMnxTi3O18 (0 ≤ x ≤ 0.8)

The n = 5 Aurivillius phase ceramics Bi6Fe2−xMnxTi3O18 (BFMTO) (0 ≤ x ≤ 0.8) were synthesized with a conventional solid-state reaction method.

Synthesis and Characterization of Bi6FeMTi3O18 (M = Mn, Fe, Co, and Ni) Aurivillius Phase Ceramics

Bi6FeMTi3O18 (M = Mn, Fe, Co, and Ni) ceramics were sintered using conventional mixed oxide route. The crystallographic structures of four samples are determined to be the typical five-layer Aurivillius phase. At room temperature (RT), the ferroelectric (P-E) loop of Bi6FeMnTi3O18 (BFMT) exhibits a certain degree of current leakage, the remnant polarization (2Pr) of Bi6FeFeTi3O18 (BFFT), Bi6FeCoTi3O18 (BFCT), and Bi6FeMnTi3O18 (BFNT) samples are measured to be 11.2μC/cm2, 4.3μC/cm2, and 9.8μC/cm2, respectively. The BFMT and BFFT samples show relative weak ferromagnetism/paramagnetism, while the BFCT and BFNT samples exhibit prominent ferromagnetism with the remnant magnetization (2Mr) of 0.81 emu/g and 0.46 emu/g, respectively.

Ferroelectric and piezoelectric properties of Aurivillius phase intergrowth ferroelectrics and the underlying materials design

AbstractFerroelectric and piezoelectric properties of the La‐doped intergrowth Aurivillius phase ceramics Bi5−xLaxTiNbWO15 and Bi7−xLaxTi4NbO21 (x = 0.00–1.75) were studied. It was found that the La doping is in favour of the domain switching. Owing to the impact of defects, the P–E hysteresis loops of the La‐doped Bi5TiNbWO15 ceramics are un‐symmetrical and the piezoelectric coefficients are quite low. Enhanced ferro‐/piezoelectric properties, such as 2Pr of 24.4 µC/cm2 (x = 0.50) and d33 of 16.6 pC/N (x = 0.75), were obtained in the Bi7−xLaxTi4NbO21 ceramics. The high temperature electrical behaviour indicates that the Bi5−xLaxTiNbWO15 ceramics are semiconducting whereas the La‐doped Bi7Ti4NbO21 ceramics are worthy to be further studied toward high temperature piezoelectric applications. Finally, the underlying materials design is discussed.

The grain size effect on the properties of Aurivillius phaseBi3.15Nd0.85Ti3O12 ferroelectric ceramics

Aurivillius phase, bismuth layer structured ferroelectricBi3.15Nd0.85Ti3O12 (BNdT) ceramics with average grain sizes from 90 nm and high densities (>97%) were fabricated by spark plasma sintering. Decreasing grain size produceda diffuse ferro–paraelectric phase transition and a decrease in the Curiepoint. Compared with BNdT ceramics with grain sizes of micrometre scale,nanograined BNdT ceramics exhibit a depression of the dielectric maximumat the Curie point, enhanced dielectric constant from room temperature to350 °C and dramatically decreased losses. Although ferroelectric switching was greatly inhibited innanograined ceramics, both ferroelectric and piezoelectric measurements still clearlyshowed that BNdT ceramics with 90 nm average grain sizes are ferroelectrically switchable.This is the first reported evidence that nanoscale Aurivillius phase ceramics areferroelectrically active.

The effect of Nd substitution on the electrical properties of Bi3NbTiO9 Aurivillius phase ceramics

The effect of Nd substitution on the microstructures and electrical properties of Aurivillius phase ferroelectric Bi3NbTiO9-based ceramics has been studied. All of the Bi3−xNdxNbTiO9 (0≤x≤1) ceramics are ferroelectrics. The Curie point TC decreased with increasing Nd doping content x. The Bi3−xNdxNbTiO9 ceramics exhibited a sharp ferroelectric-paraelectric phase transition at small x values (x≤0.6), whereas a diffuse phase transition was observed at higher x values (x≥0.8). Both the piezoelectric constant d33 and the dc electrical resistivity of Bi3NbTiO9 ceramics were greatly enhanced by Nd substitution on the A sites. The improved properties can be attributed to the fact that Nd substitution depressed the generation of oxygen vacancies. A combination of high d33 values, high resistivity, and high TC points (&amp;gt;700 °C) suggests that the Bi3−xNdxNbTiO9 ceramics with x≤0.6 could be good candidates for high-temperature piezoelectric applications.