SrBi2Nb2O9 Research Articles

Ionic Doping Effects in SrBi2Nb2O9 Ferroelectric Ceramics

Ionic doping effects of various ions in Bi-layered ferroelectric SrBi2Nb2O9 (SBN) ceramics were studied. Un-doped and doped SBN ceramics with Ba2+, Pb2+, Ca2+, Bi3+, La3+, Ti4+, Mo6+, and W6+ ions were made with solid state reactions. Temperature dependent dielectric constants were measured. Ferroelectric transition temperature (TC) decreased with Ba2+ and Pb2+ ions but increased with Ca2+ ion which substitutes the 12-coordinated Sr2+ site. TC increased with Ti4+, Mo6+, and W6+ ions which substitute the 6-coordinated Nb5+ sites. With trivalent Bi3+ and La3+ ions, TC increased with Bi3+ ion but much decreased with La3+ ion. These results showed that the ion size plays an important role in ferroelectricity of SBN ceramics.

SrBi 2 Nb 2 O 9 thin films epitaxially grown on Pt epitaxial bottom layers: structural characteristics and nanoscale characterization of the ferroelectric behaviour by AFM

SrBi2Nb2O9 (SBN) films were grown by pulsed laser deposition on (100) and (110) Pt epitaxial bottom layers. In both cases x-ray diffraction evidenced the epitaxial growth of SBN in spite of the coexistence of mainly two orientations. SBN films on (100) Pt present usually a dominant (001) orientation with the (115) one. AFM piezoresponse images agree with the crystallographic data, i.e. only the (115) oriented grains show a piezoelectric contrast. The SBN films grown on (110) Pt lead to a more homogenous piezoresponse imaging, in agreement with the preferential (116) orientation and the microstructure.

Pulsed laser deposited SrBi2Nb2O9 thin films grown on various substrates compatible with microwaves applications

AbstractSrBi2Nb2O9 (SBN) films were grown by pulsed laser deposition on various substrates suitable for microwaves applications. Pure c‐axis oriented SBN films on (100) MgO and (100) LaAlO3 are epitaxially grown. The crystalline quality evaluated by the rocking curves width is strongly correlated to the film‐substrate mismatch (Δohgr; = 0.9–2° on MgO and Δω = 0.3–0.4° on LaAlO3). SBN growth on sapphire is more complex. In fact, on R‐plane as well as on C‐plane, XRD evidences the coexistence of various orientations of the SBN films. In spite of the coexistence of several orientations epitaxial growth was evidenced, strongly influencing the microstructure.

Cathodoluminescence of selected single ZnO nanowires on sapphire

SrBi2Nb2O9 (SBN) films were grown by pulsed laser deposition on (100) and (110) Pt epitaxial bottom layers. In both cases x-ray diffraction evidenced the epitaxial growth of SBN in spite of the coexistence of mainly two orientations. SBN films on (100) Pt present usually a dominant (001) orientation with the (115) one. AFM piezoresponse images agree with the crystallographic data, i.e. only the (115) oriented grains show a piezoelectric contrast. The SBN films grown on (110) Pt lead to a more homogenous piezoresponse imaging, in agreement with the preferential (116) orientation and the microstructure.

Oxygen plasma rapid thermal annealing to improve the electrical properties of Pt–SrBi[sub 2]Nb[sub 2]O[sub 9]–SiO[sub 2]–Si gate structure

A rapid thermal annealing (RTA) method in oxygen plasma improves the ferroelectric properties of SrBi2Nb2O9 (SBN) film at relatively lower temperature than the conventional furnace annealing in oxygen ambient. The oxygen plasma RTA raises the oxygen content from 44 to 48 at. %, which may improve the oxygen deficiency in the SBN films. The thickness of SiO2 becomes thinner due to the shorter RTA time. As a result, a typical effective memory window of the Pt–SBN–SiO2–Si gate structure is increased from 0.17 to 0.49 V at 3 V of the applied gate bias and the remnant polarization is also increased from 18.03 to 22.6 C/cm2 at ±6 V. The flat band voltage shift of the oxygen plasma RTA samples is quite stable and smaller than that of the furnace annealed ones because charge trapping is relatively smaller at the interface between Si and the oxygen plasma annealed SBN film.

Transmission electron microscopy study of domain structures in ferroelectric SrBi2Nb2O9 ceramics

ABSTRACTA transmission electron microscopy study has been carried out on the domain structures of SrBi2Nb2O9 (SBN) ferroelectric ceramics which belong to the Aurivillius family of bismuth layered perovskite oxides. SBN is a potential candidate for Ferroelectric Random access memory (FeRAM) applications. The 90° ferroelectric domains and antiphase boundaries (APBs) were identified with dark field imaging techniques using different superlattice reflections which arise as a consequence of octahedral rotations and cationic shifts. The 90° domain walls are irregular in shape without any faceting. The antiphase boundaries are less dense compared to that of SrBi2Ta2O9(SBT). The electron microscopy observations are correlated with the polarization fatigue nature of the ceramic where the domain structures possibly play a key role in the fatigue- free behavior of the Aurivillius family of ferroelectric oxides.

Improvement of ferroelectric properties of Pt–SrBi2Nb2O9–SiO2–Si gate structure through oxygen plasma rapid thermal annealing

A rapid thermal annealing (RTA) method in oxygen plasma improves the ferroelectric properties of SrBi2Nb2O9 (SBN) film at relatively lower temperature compared with the conventional furnace annealing in an oxygen ambient. The oxygen plasma RTA is assumed to improve the oxygen deficiency in the SBN films by increasing the oxygen content from 44 to 48 at%. The thickness of SiO2 becomes less in substantially less time, thereby improving the memory window of the Pt–SBN–SiO2–Si gate structure. The typical effective memory window is increased from 0.17 to 0.49 V at 3 V of the applied gate bias and the double remnant polarization (2Pr) is also increased from 18.03 to 22.6 μC/cm2. The flat-band voltage shift in the case of oxygen plasma RTA is quite stable and smaller than that in the case of furnace annealing because charge trapping is relatively less at the interface between Si and the oxygen plasma RTA-annealed SBN film. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Properties of the Elastic Anomaly in SrBi2Nb2O9-based Ceramics

A study was conducted on the effects of compositional modifications on the temperature coefficient of resonance frequency (TCF) in the disc planar vibration mode for the bismuth layer-structured compound SrBi2Nb2O9 (SBN)-based ceramics. The substitution of the strontium site by divalent and trivalent ions improved the TCF, accompanying the relaxation of elastic anomaly. The tolerance factor, t, was calculated for a pseudo cubic block to study the contribution of the structural factor to Curie temperature, TC, and the temperature of elastic anomaly, Tea, for each sample. Tea showed no apparent tendency with t, whereas TC increased as t decreased.

Growth and characterization of Al2O3 thin films for the buffer insulator in Pt/SrBi2Nb2O9/Al2O3/Si ferroelectric gate oxide structure

Pt/SrBi2Nb2O9 (SBN)/Al2O3/Si (MFIS) ferroelectric gate oxide structures were prepared with the rf (radio frequency) magnetron sputtering method for the application of non-destructive read-out ferroelectric RAM (NDRO-FRAM) devices. An Al2O3 intermediate layer between the perovskite SrBi2Nb2O9 film and Si substrate prevents the serious inter-diffusion of the SrBi2Nb2O9 (SBN) into the Si substrate. The coercive field that decisively affects the memory window was increased by inserting the Al2O3 insulator between the SBN and Si, and thus the memory window also increased with the increase in the electric field to the SBN. The memory windows of the metal-ferroelectric-insulator-semiconductors (MFIS) structures were in the range of 0.7–3.4 V when the gate voltage varied from 3 to 9 V. The memory windows of the MFIS structures were found to be dependent on the thickness and stoichiometry of the buffer layer. We obtained the maximum memory window in an MFIS with an insulator of 11.4 nm in thickness deposited in the deposition condition of a 15∶5 flow ratio (Ar:O2) during sputtering.

Piezoelectric Properties of Ba and Ca Doped SrBi2Nb2O9 Based Ceramic Materials

The crystalline structure and dielectric and piezoelectric properties of SrBi2Nb2O9 (SBN)-based materials were investigated with the substitution of Ca and Ba ions into the Sr site in this study. X-ray diffraction analysis revealed that these substitutes formed solid solutions throughout the compositions. The Ca substitution increases the ferroelectric transition temperature and maintains the phase transition as that of the normal ferroelectrics, while the Ba substitution lowers the ferroelectric transition temperatures and changes the transition from the normal to the diffuse ferroelectric one. The Ba-substituted SBN shows a smooth elastic anomaly for the Ba substitution of 0.2. A dielectric measurement revealed that the smooth elastic anomaly might be related to small dielectric dispersion characteristics observed around 300°C.

Structural characterization of thin films of the SrBi2Nb2O9ferroelectric Aurivillius phase epitaxially grown on (110)SrTiO3

Aurivillius-phase SrBi2Nb2O9(SBN) films grown by pulsed-laser deposition on (110)SrTiO3are nearly (116) oriented as shown by their X-ray diffraction θ–2θ scans. A specific artifact, leading possibly to an erroneous deduction of a (115) and (116) mixture of orientations, has been highlighted. The films present a quite small mosaicity (ω-scan full width at half-maximum = 0.2–0.5°). Sharp electron channeling patterns (ECPs) with the expected twofold symmetry are the signature of film epitaxy. These ECPs often display the superimposition of two individual patterns, rotated by 180° with respect to each other: two families of oriented SBN crystallites, rotated in the same way, coexist in the films. Indeed, from symmetry considerations at the film–substrate interface, these two families area prioriequiprobable. Similarly, two peaks, 180° shifted, are observed for the 00 10 reflection φ scans and fully confirm this model. However, their relative intensity, which gives access to the quantitative distribution of the two families, shows that in many cases the two families do not present the same relative weight, in good correlation with the qualitative ECP observations, indicating a subtle asymmetrization at the nucleation or growth stage. The in-plane orientation is defined as: [\bar{1}10]F|| [001]Sand nearly [33\bar{1}]For [\bar{3}\bar{3}1]F|| [\bar{1}10]S(generating the two families). The film–substrate interfacial relationship is discussed, taking into account the possible facetting of the substrate surface and the occurrence of the (11\bar{7}) SBN plane as twin boundary.

Aqueous solution-gel synthesis of strontium bismuth niobate (SrBi2Nb2O9)

The synthesis of multimetal oxides containing pentavalent elements like Nb and Ta out of an aqueous solution is very complicated due to the extremely high sensitivity of these metals towards hydrolysis. Moreover the only water-soluble starting compound is the oxalate which is not very suited for gel formation. Nevertheless, from Nb-oxalate it is possible to prepare a water-soluble Nb(V)-precursor by chemical modification. The synthesized precursor remains stable in the pH-range needed for gel formation. This Nb(V)-precursor is used for the synthesis of the ferroelectric material SrBi2Nb2O9 (SBN). An aqueous acetate-citrate solution-gel precursor for SBN was prepared. The chemical homogeneity of this precursor was investigated by means of TEM-experiments. All metal ions were found to be homogeneously dispersed in the precursor gel at least down to 10 nm. The SBN phase formation is followed by means of X-ray Diffraction. It has been shown that the perovskite phase already forms at 550°C.

High Remanent Polarization in Laser Ablated SrBi2Nb2O9Thin Films

AbstractPulsed-laser-deposition technique was used to grow SrBi2Nb2O9(SBN) thin films on platinized silicon substrates. The effect of annealing temperature and film thicknesses on the structural and electrical properties has been studied. The average grain size and rms surface roughness was found to increase with increasing annealing temperature. The degree of orientation along the (200) direction was increased with the film thicknesses. The remanent polarization was found to be increased with the film thicknesses and was attributed to the selftexturing characteristics of SBN films. Thin films with higher thickness (∼570 nm) exhibited high value of remanent polarization (∼38 ν/cm2) with coercive field of 185 kV/cm. There was a reduction of coercive field with the film thickness. The dielectric constant was observed to be independent of the film thickness. The increase in loss tangent with increasing film thicknesses was attributed to the reduction of dielectric breakdown strength of the films. The SBN thin films showed minimal fatigue characteristics and suitable material for memory devices.

Fine-Tolerance Resonator Applications of Bismuth-Layer-Structured Ferroelectric Ceramics

The two-layered SrBi2Nb2O9 (SBN) ceramic resonator that generates second harmonics of the thickness extensional vibration is a strong candidate for fine-tolerance-resonator applications, because of its small electromechanical coupling coefficient and high temperature stability. The Nd substitution of Sr in SBN is effective in further decreasing the temperature coefficient of resonance frequency (TCF) while maintaining its high maximum value of electrical quality factor (Qemax) at a resonance frequency. On the other hand, a grain-oriented SBN-type ceramic resonator has an attractive property of thickness shear vibration. The temperature coefficient of oscillation frequency (TCO) could be less than 10 ppm/°C in an ordinary oscillation circuit with grain-oriented SBN-type ceramics. In this paper, we describe how a fine tolerance resonator can be realized using compositional and structural designs of the bismuth-layer-structured ferroelectric (BLSF) ceramic resonator.

Enhanced ferroelectric properties in laser-ablated SrBi2Nb2O9 thin films on platinized silicon substrate

Non-c-axis-oriented SrBi2Nb2O9 (SBN) thin films were grown on Pt/TiO2/SiO2/Si substrates using the pulsed-laser-deposition technique. X-ray diffraction results confirmed the textured growth of SBN thin films along (115) and (200) orientations. The increase in the value of the dielectric permittivity and decrease in the tangential loss of the films with an increase in annealing temperature were attributed to grain size dependence. SBN thin films annealed at 750 °C exhibited a maximum value of the dielectric constant of ∼346 with a dissipation factor of 0.02. Thin films with certain deposition parameters exhibited the highest remanent polarization (Pr) and coercive field, 25.7 μC/cm2 and 198 kV/cm, respectively. There was minimal (<20%) degradation in the switchable polarization (P*−P∧) after 1010 switching cycles. At lower field, the leakage current follows ohmic behavior, and at higher field, up to 100 kV/cm, the leakage current density was about 5×10−7 A/cm2.

Leakage current characteristics of laser-ablated SrBi2Nb2O9 thin films

We have studied the leakage current conduction mechanism of pulsed-laser-deposited SrBi2Nb2O9 (SBN) thin films on platinized silicon substrates. The time-dependent dc leakage current densities of SBN thin films do not follow Curie–von Schweidler power law. Instead the contribution of conduction current is predominantly electronic. At lower fields, the leakage current follows the ohmic behavior, and it increases exponentially for higher fields. The leakage current density of the SBN thin films was studied at elevated temperatures, and the data were fitted with the Schottky emission model. The effective Richardson’s constant was calculated to be about 8.7×10−6 A/cm2 K2. The Schottky barrier height of the SBN thin films was estimated to be 1.37 eV.

Electronic properties of ferroelectric SrBi2Ta2O9, SrBi2Nb2O9, and PbBi2Nb2O9 with optimized structures

Electronic properties of ferroelectric SrBi2Ta2O9 (SBT) SrBi2Nb2O9 (SBN) and PbBi2Nb2O9 (PBN) have been investigated using a first-principles calculational method with optimized structures. In optimized SBT, the displacement of Ta in TaO6 octahedra is small, while the displacement of Nb in NbO6 octahedra is larger in optimized SBN. In optimized PBN, on the other hand, due to the hybridization between Pb 6s and O 2p, the displacement of NbO6 octahedra is larger than that in SBN.

Ferroelectric Properties in Ca Substituted SrBi2Nb2O9 Thin Films

ABSTRACTWe have studied the influence of partial substitution of Ca (0%, 5%, 10% and 15%) on the structural and electrical properties of SrBi2Nb2O9 (SBN) thin films. Pulsed laser deposition technique was used to grow thin films on platinized silicon substrates. X-ray diffraction data confirmed the polycrystalline nature of the films with preferential orientation along the polarization axis. Incorporation of Ca at Sr-site of SBN reduced the lattice parameter and was attributed to the smaller ionic radii of Ca. The soft mode frequency at 29.5 cm-1 of SBN shifted towards higher wavenumber implied increasing the transition temperature upon Ca substitution. The grain sizes of SBN thin films vary from oval to rod like structures and improving the homogeneous distribution of grains with the increase in Ca contents. The ferroelectric properties of the films enhanced with maximum remanent polarization of 35.3 mC/cm2. The increase in the coercive field with incorporation of Ca at Sr-site was attributed to the higher electronegativity of Ca. The SBN thin films with the incoporation of Ca exhibited poor leakage current behavior. The reduction of dielectric permittivity with Ca concentration was attributed to the lower dielectric permittivity of CaBi2Nb2O9.

Processing and Properties of Strontium Bismuth Vanadate Niobate Ferroelectric Ceramics

The processing conditions, microstructure, and dielectric properties of strontium bismuth niobate vanadate ceramics, SrBi2(VxNb1−x)2O9 (SBVN, with 0 ≤x≤ 0.3), were systematically studied. A relative density of >90% was obtained for all the samples using a two‐step sintering process. XRD showed that a single phase with the layered perovskite structure of SrBi2Nb2O9 (SBN) was formed with a vanadium content of up to 30 at.%. SEM revealed that the average grain size decreased gradually with an increase in vanadium content. The Curie point was found to gradually increase from ∼418°C for SBN to ∼459°C for SBVN with 30 at.% vanadium. Dielectric constants at room temperature and their respective Curie points were found to peak at a composition with 10–15 at.%; vanadium. Moreover, a high concentration of vanadium (>5 at.%) resulted in a significant increase in tangent loss at low frequencies (<1000 Hz). The relationships between chemical composition, processing condition, microstructure, and dielectric properties of SBVN ferroelectric ceramics are discussed.

Composition control of SBN thin films deposited by PLD on various substrates

Thin films of SrBi2Nb2O9 (SBN) have been grown on both Pt/Ti/SiO2/Si and (100)MgO substrates by pulsed laser deposition. In the Sr–Bi–Nb–O system, the loss of bismuth during the process due to its volatility results obviously in a non-respect of the stoichiometry of the films and the presence of secondary phases. In order to maintain the right composition of the films, two different ways were experimented. On Pt/Ti/SiO2/Si, a sequential deposition from home-made Bi2O3 and SBN sintered targets as well as the use of Bi-enriched targets allows to obtain stoichiometric ferroelectric films. Various parameters like deposition time and periodicity of the Bi2O3 and SBN layers are of first importance. On (100)MgO which promotes SBN epitaxial growth, this sequential deposition is not suitable and we succeeded in the control of the Bi/(Sr+Nb) ratio only by using Bi-enriched targets.