Bismuth-layered Perovskite Structure Research Articles

The Electric Conductivity of Bi7Fe3Ti3O21 Doped with Gadolinium.

Bi7-xGdxFe3Ti3O21 (x = (0, 0.2, 0.4, 0.6)) bismuth-layered perovskite structure compounds have been successfully prepared by a solid-state reaction. The results of X-ray studies indicate that a single-phase ceramic was obtained, characterized by an orthorhombic crystal structure for all compounds within the Fm2m space group. Microstructural analysis revealed that introducing gadolinium to the material altered the grain morphology, resulting in a more rounded grain shape and a somewhat disordered arrangement. Moreover, with higher gadolinium concentrations, there is a noticeable increase in the presence of the number of large plates. Impedance spectroscopy has been used to characterize the electrical properties of Bi7-xGdxFe3Ti3O21 compounds.

Tailoring the optical properties of SrBi4Ti4O15 thin films by RF sputtering process parameters

SrBi4Ti4O15 is a bismuth layered perovskite structure material, its thin film form gained much interest due to their geometrical flexibility and thickness. In the present study, SrBi4Ti4O15 thin films are deposited on amorphous substrate using radio frequency sputtering technique. SrBi4Ti4O15 thin films found to be single phase orthorhombic structure by using X-ray diffraction technique. Surface morphology studies such as grain size, shape and roughness were explored through atomic force microscopy. EDX analysis identified the individual elements and its percentage in the compound. Optical properties (refractive index and bandgap) were determined with varying the oxygen mixing percentage (OMP). The best optical properties (refractive index ~ 2.35 and bandgap ~ 3.4 eV) were obtained for films deposited at 50% OMP. These results shows the potential of using SrBi4Ti4O15 thin films in electro-optic devices.

Effect of the thickness of Sr2Bi4Ti5O18 transition layer on the properties of BiFeO3/Sr2Bi4Ti5O18 bilayer composite thin films

BiFeO3(BFO)/Sr2Bi4Ti5O18(SBT) bilayer composite thin films were prepared using the sol-gel method. The influence of the SBT transition layer thickness on the properties of BFO/SBT bilayer composite thin films was studied. The results showed that an SBT transition layer with the proper thickness can improve the BFO/SBT bilayer composite film performance. X-ray diffraction (XRD) analysis revealed that a bismuth layered perovskite structure is formed in all of the thin films. The scanning electron microscopy (SEM) result showed that the BFO/80 nmSBT sample exhibits good crystallization, an improved density and a uniform minimum grain size compared with the other samples. The X-ray photoelectron spectroscopy (XPS) result showed that the Fe2+ content and oxygen vacancy concentration are lowest in the BFO/80 nm SBT sample. This sample has good ferroelectric properties: the leakage current density has the lowest value of J = 5.21 × 10-5 A/cm2 among the samples at 350 kV/cm, 2Ec = 900 kV/cm, and 2Pr = 151 μC/cm2. At a low electric field (E<100 kV/cm), the leakage mechanism of the thin film is ohmic conduction, and the Fowler-Nordheim (F–N) tunneling effect is observed at a high electric field (E>100 kV/cm). The relative dielectric constant (εr) is 121, the dielectric loss (tanδ) is 0.024 at 105 Hz.

Effect of Ca doping on the properties of Sr2Bi4Ti5O18 ferroelectric thin films

This study examined the effect of Ca doping on the properties of Sr2Bi4Ti5O18 (SBTi) ferroelectric thin films. According to the results of the study, the performance of SBTi thin films are improved by suitable Ca doping. It can be seen from XRD analysis, all of the thin films formed a bismuth layered perovskite structure without other impure phases. SEM shows that the sample with a doping content of 10 mol% has good crystallization, uniform grain size and good film density. Compared with the characteristics of other films, the thin film sample with 10 mol% Ca shows high crystallinity, the lowest Ti3+ content, the lowest oxygen vacancy concentration, and with the large remanent polarization 2Pr = 33.5 μC/cm2, the double coercive field 2Ec = 182.8 kV/cm; furthermore, the leakage current density is 1.67 × 10−7 A/cm2. The film sample doped with 10 mol% Ca also displays better dielectric properties, with a larger dielectric constant (er = 795) and lower dielectric loss (tanδ = 0.03) when the test frequency is 105 Hz. The dielectric tunability T = 18.6% at 200 kV/cm and 500 kHz.

Strong magnetoelectric effect of Bi4Ti3O12/Bi5Ti3FeO15 composite films

Bi4Ti3O12/Bi5Ti3FeO15 composite films were prepared by chemistry solution deposition. The microstructure, ferroelectric properties, piezoelectric properties, magnetic properties as well as magnetoelectric effect were investigated for the composite films. It is shown that the composite films display well-defined microstructure with the clear interface. Compared with the pure Bi4Ti3O12 or Bi5Ti3FeO15 films, the composite films not only exhibit enhanced ferromagnetic and ferroelectric properties, but also possess strong magnetoelectric effect. Thus enhanced multiferroic and magnetoelectric properties are attributed to the similar bismuth-layered perovskite structure between Bi5Ti3FeO15 and Bi4Ti3O12 films, which leads to a strong coupling interaction between ferromagnetic and ferroelectric phases. The present work provides a feasible way of preparing magnetoelectric composite films and facilitating their applications on micro-electro-mechanical system and information storage devices.

Enhanced up-conversion photoluminescence and dielectric properties of Er- and Zr-codoped strontium bismuth niobate ceramics

Er- and Zr-codoped strontium bismuth niobate ceramics, Sr0.97Er0.03Bi2Nb2−xZrxO9 (SBNx) with different x (0≤x≤0.1), were synthesized by the solid state reaction method. Their structural, up-conversion (UC) photoluminescence, and dielectric properties were investigated. By Rietveld structural refinement, all SBNx samples exhibited a polycrystalline bismuth-layered perovskite structure with space group A21am. With deliberate introduction of Zr4+ ions in the bismuth-layered perovskite structure, SBNx samples presented simultaneously enhanced UC photoluminescence and dielectric properties. The UC photoluminescence was investigated as a function of Zr4+ concentration and incident pump power. Under the 980nm near infrared (NIR) excitation, bright UC green and weak red emissions were observed which corresponded to the transitions from 2H11/2/4S3/2 and 4F9/2 to 4I15/2 level, respectively. With x increase, the UC luminescence improvement of SBNx can be attributed to the local distortion of crystal field surrounding the Er3+ activator which induced by different ionic radii of Zr4+ and Nb5+ ions. The dependence of UC emission intensity on pumping power showed that two photon energy transfer process was involved in the UC green and red emissions. Furthermore, electrical measurements indicated that the introduction of Zr4+ distinctly increased the ferroelectric to paraelectric phase transition temperature (TC) of SBNx ceramics from 724K to 762K as x ranging from 0.0 to 0.1. It is believed that B site doping in SBNx by large Zr4+ ion is an effective method to improve UC luminescence and electrical properties of this potentially multifunctional optical-electro material.

Tuning the Physical Properties of BNT Ferroelectric Film by Miscut Si Substrate

The electrical and domain switching properties of Bi3.15Nd0.85Ti3O12 (BNT) thin films have been studied, which were prepared by pulse laser deposition (PLD) on exact and miscut (2°) Si substrates. The films have a bismuth-layered perovskite structure, and the leakage current of BNT film on miscut substrate is smaller than that on exact one. The domain structure, domain switching and hysteresis loops of BNT film on miscut substrate were studied, multidirectional domain structure, complete domain switching and strong piezoresponse are found in it. The phase-voltage hysteresis and butterfly loops were very saturated with a coercive voltage (Vc) about 3.75 V. The film also exhibited excellent piezoelectric property with a high piezoelectric coefficient d33~20 pm/V.

Structural, ferroelectric and leakage current properties of Bi3.96Pr0.04Ti2.95Nb0.05O12 thin films

Praseodymium and niobium-substituted bismuth titanate (Bi3.96Pr0.04Ti2.95Nb0.05O12, BPTNO) thin films were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by a sol–gel technology. The effects of annealing temperature (500~800°C) on microstructure and electric properties of thin films were investigated. X-ray diffraction analysis shows that the BPTNO thin films have a bismuth-layered perovskite structure with preferred (117) orientation. The intensities of (117) peak increases with increasing annealing temperature. With the increase of annealing temperature from 500°C to 800°C, the grain size of BPTNO thin films increases. The highly (117)-oriented BPTNO thin films exhibits a high remnant polarization (2Pr) of 48μC/cm2 and a low coercive field (2Ec) of 110kV/cm, fatigue free characteristics up to >108 switching cycles. A small leakage current density (J) was 6.23×10−8A/cm2 at 200kV/cm. The leakage current mechanisms were controlled by Poole–Frenkel emission in the low electric field region and by Schottky emission in the high field region.

Leakage mechanisms in rare-earth (La, Nd) doped Bi4Ti3O12 ferroelectric ceramics

Dense Bi4Ti3O12 (BTO), Bi3.15La0.85Ti3O12 (BLaT) and Bi3.15Nd0.85Ti3O12 (BNdT) ferroelectric ceramics were synthesized by solid–state reaction method. All ceramics are orthorhombic bismuth-layered perovskite structure with plate-like grains of random orientation. The influences of La and Nd doping on the ferroelectric properties and leakage mechanism were investigated. The remanent polarizations (2P r) were determined to be 13.4, 23.9 and 32.6 μC/cm2 for BTO, BLaT, and BNdT, respectively. The leakage current density decreased markedly with La and Nd doping. The dominant leakage mechanism in both BTO and BLaT ceramics has been found to be the ohmic mechanism and the space-charge-limited current mechanism in the low and high electric field region, respectively. While in BNdT ceramics a quasi-ohmic behavior was found in the high electric field region, following the ohmic behavior in the low electric field region and trapped filled limited behavior in the intermediate electric field region.

IMPEDANCE SPECTROSCOPY AND MAGNETIC PROPERTIES OF AURIVILLIUS STRUCTURES

Bi 9-x Fe 5+x Ti 3 O 27 (x = 0-3) compounds of bismuth layered perovskite structure have been successfully prepared by solid-state reaction method. X-ray diffraction (XRD) studies revealed the orthorhombic crystal structure of all the compounds. Impedance spectroscopy has been studied to characterize the electrical properties of polycrystalline Bi 9-x Fe 5+x Ti 3 O 27 (x = 0-3) compounds. The shape of complex impedance curves inferred the contribution of bulk and grain boundary effects on the electrical properties of the compounds. Temperature dependent magnetization measurements were made from 2 K to 300 K. Narrow hysteresis loops observed at room temperature indicate antiferromagnetic behavior of the compounds.

Structural and Electrical Properties of Lanthanide Substituted-Bismuth Titanate Prepared by Low-Temperature Combustion Synthesis

This paper elucidates the structural and electrical properties of Bi4Ti3O12 (BIT), Bi3.25Nd0.75Ti3O12 (BNT075) and Bi3.25La0.75Ti3O12 (BLT075) compounds that were primarily prepared by a novel combustion route at temperature as low as 300°C. Single crystalline phase of bismuth-layered perovskite structure was obtained directly after combustion without calcination. X-ray diffraction and Raman spectra analysis showed the phase transition from orthorhombic to tetragonal symmetry with substituting compounds. Compared to BIT, the Curie temperature at maximum dielectric peak of BNT075 and BLT075 decreased to lower values of 434°C and 365°C, respectively. The loss tangen for corresponding substitution compounds were 5 times lower than that of BIT. Besides, BNT075 resulted in large remanent polarization (2Pr) and coercive field (Ec) values of 19µC/cm2 and 45kV/cm, respectively, while 17.6µC/cm2 and 42kV/cm for BLT075.

Optical characteristics of Bi4-xEuxTi3O12 ferroelectric thin films on fused silica substrates

Bi4-xEuxTi3O12 (BEuT) ferroelectric thin films were prepared on fused silica substrates by using chemical solution deposition technique. The attained samples had a polycrystalline bismuth-layered perovskite structure, and their optical properties were composition dependent. The thin film samples had good optical transmittance above 500 nm wavelength. A blue shift of the optical absorption edge was observed in the BEuT thin films with increasing Eu3+ concentration. The optical band gaps of BEuT thin films were estimated to be about 3.57, 3.60, 3.61, 3.63, and 3.69 eV for the samples with x = 0.25, 0.40, 0.55, 0.70, and 0.85, respectively. Photoluminescence measurements showed that two emission peaks of BEuT thin films originated from two transitions of 5 D 0 → 7 F 1 (594 nm) and 5 D 0 → 7 F 2 (617 nm) had maximum intensities when Eu3+ concentration was x = 0.40. The relatively high quenching concentration of Eu3+ content was thought to be related to the layered structure of BEuT thin films. These results suggested that multifunctional BEuT thin film materials could have promising applications in optoelectronic devices.

Domain structures in hot-press sintered SrBi2Ta1.6Nb0.4O9 and SrBi2Ta2O9 ferroelectric ceramics

SrBi2Ta1.6Nb0.4O9 (SBTN) and SrBi2Ta2O9 (SBT) ceramics with typical bismuth layered perovskite structure were synthesized by hot-press sintering at 1000°C for 2h. The maximum relative density of as-sintered SBTN and SBT materials is 98.97%. The domain structure of SBTN and SBT was systemically characterized by means of TEM and HRTEM. The 90° domain walls were identified by the 90° rotation relationship of the electron diffraction pattern along the [001] zone axis. Irregular shaped and highly curved 180° domain wall were also observed in SBTN ceramics. The traditional α-fringes can be found in SBT, which are the evidence of large strains in hot-press sintering ceramics. Rod-like SrTa2O6 precipitates are also analyzed as well as its interface with the matrix.

Effects of tantalum doping on microstructure and ferroelectric properties of Bi 4Ti 3O 12 thin films prepared by a sol–gel method

Tantalum-substituted Bi 4Ti 3O 12 (Bi 4Ti 3- x/5 Ta x/5 O 12, BTTO) thin films were fabricated on Pt(111)/Ti/SiO 2/Si(100) substrates by sol–gel technology. The effects of various processing parameters, including Ta content ( x=0∼0.08) and annealing temperature (500∼800 °C), on the growth and properties of thin films were investigated. X-ray diffraction analysis shows that the BTTO thin films have a bismuth-layered perovskite structure with preferred (117) orientation. With the increase of Ta content, the grain size of film decreased slightly, and highly (117)-oriented BTTO films were obtained in the composition of x=0.06. Ta doping on the B-site of Bi 4Ti 3O 12 could induce the distortion of oxygen octahedral and decrease the oxygen vacancy concentration by a compensating effect. The highly (117)-oriented BTTO thin films with x=0.06 exhibits the maximum remanent polarization (2 P r) of 50 μC/cm 2 and a low coercive field (2 E c) of 104 kV/cm, fatigue free characteristics up to ≧ 10 8 switching cycles.

Effects of Film Thickness on Microstructure and Ferroelectric Properties of Bi&lt;sub&gt;3.15&lt;/sub&gt;Nd&lt;sub&gt;0.85&lt;/sub&gt;Ti&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;12&lt;/sub&gt; Thin Films Prepared by Sol-Gel Method

Bi3.15Nd0.85Ti3O12 (BNT) thin films with different thicknesses (200, 270, 360, 450 and 540 nm) were prepared on Pt/Ti/SiO2/Si substrates by sol–gel method. The effect of film thickness on the microstructure and ferroelectric properties of BNT thin films was investigated. All BNT thin films were consisted of a single phase of bismuth-layered perovskite structure. With increasing film thickness, grains gradually became larger, the remanent polarization (2Pr) firstly increased and then decreased, and the leakage current density showed opposite trend. The 360 nm-thick BNT film exhibited better electrical properties with 2Pr 26 µC/cm2, coercive field (2Ec) 220 kV/cm, dielectric constant 345 (at 1 MHz) and low leakage current density.

Hydrothermal Synthesis and Optical Properties of Single-Crystalline Bi&lt;SUB&gt;3.15&lt;/SUB&gt;Nd&lt;SUB&gt;0.85&lt;/SUB&gt;Ti&lt;SUB&gt;3&lt;/SUB&gt;O&lt;SUB&gt;12&lt;/SUB&gt; Nanoplates of Layered-Perovskite Structure

Single-crystalline Bi3.15Nd0.85Ti3O12 (BNdT) nanoplates of bismuth-layered perovskite structure have been synthesized through hydrothermal process. The BNdT nanoplates possess well-defined tetragonal shapes with landscape dimension of 100-600 nm and thickness of 10-30 nm. The in-plane surfaces of tetragonal-shaped nanoplates lies on (001), and the side surfaces are (110) and (110). The BNdT nanoplates were formed due to the rather higher growth rate of a-b plane than that of c-axis. The optical absorption characteristics in UV-visible region demonstrated that the band gap of the BNdT nanoplates is 3.33 eV. The absorption bands around 516 nm, 526 nm, 585.6 nm, 684.6 nm and 750 nm should be assigned as transitions of Nd3+ from the ground state 4I9/2 to 2G9/2, 4G7/2, 2G7/2 or 4G5/2, 4F9/2 and 4S3/2 states, respectively.

Electrical Properties and Leakage Current Mechanisms of Bi3.2Gd0.8Ti3O12 Thin Films Prepared by a Sol-Gel Method

Bi3.2Gd0.8Ti3O12 (BGTO) thin films were deposited on Pt(111)/Ti/SiO2/Si(100) substrates using the sol-gel method and rapid thermal annealing in an oxygen atmosphere. The effects of annealing temperature (500–800°C) on microstructure and electrical properties of thin films were investigated. X-ray diffraction analysis shows that the BGT thin films have a bismuth-layered perovskite structure with preferred (117) orientation. The intensities of (117) peaks increases with increasing annealing temperature. The leakage current density (J) was 3.69×10−8 A/cm2 at 200 kV/cm. It was found that the leakage current was affected not only by the microstructure but also by the interface between the Pt electrode and BGTO thin films. In the low electric field region, the leakage current was controlled by Poole–Frenkel emission. In addition, the mechanism can be explained by Schottky emission from the Pt electrode in the high electric field region.

Synthesis and characterization of Bi 3.15Nd 0.85Ti 3O 12 nanotube arrays

Nd-substituted bismuth titanate (Bi 3.15Nd 0.85Ti 3O 12, BNT) nanotube arrays are fabricated by means of a sol–gel method utilizing porous anodic aluminum oxide (AAO) template. The morphologies and structures have been determined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The diameter and length of these nanotubes are about 200 nm and 60 μm, respectively, and their wall thickness is about 30 nm. The average grain size is around 40 nm. XRD data show that the BNT nanotubes possess bismuth-layered perovskite structure. High-resolution electron microscopy (HRTEM) image demonstrates that the BNT nanotubes are polycrystalline. Polarization–electric field ( P– E) response curves of BNT nanotube arrays were measured, and a size induced polarization reduction phenomenon is observed.

Photoluminescence and ferroelectric properties of sol–gel-grown Eu-doped CaBi4Ti4O15 : Nd films

Eu-doped CaBi4Ti4O15 : Nd (CBENT) ferroelectric thin films were prepared on Pt/Ti/SiO2/Si substrates by a sol–gel method. The photoluminescence (PL) and ferroelectric properties of the films were investigated by using different annealing temperatures and concentrations of europium ions. All the CaBi3.75−xEuxNd0.25Ti4O15 films have a polycrystalline bismuth-layered perovskite structure, and a morphotropic phase boundary (MPB) between orthorhombic and tetragonal phases was shown to exist. The PL intensity of the CBENT films is significantly dependent on annealing temperature and Eu concentration. The remanent polarization 2Pr values of the Eu-doped CaBi4Ti4O15 : Nd thin films reaches a maximum value of 30.7 µC cm−2 when x is 0.2. The PL and ferroelectric properties suggest that CBENT films can be considered as promising multifunctional materials.

Hydrothermal synthesis and characterization of Bi4Ti3O12 powders

The Bi4Ti3O12 powders were synthesized by a hydrothermal route. The influence of hydrothermal conditions on crystal structures and morphologies of Bi4Ti3O12 particles was studied. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared (FT-IR) spectroscopy and ultraviolet visible (UV-vis) spectroscopy. These results revealed that the Bi4Ti3O12 powders prepared thus possessed a plate-like shape, a typical bismuth layered perovskite structure, and a wide UV-vis absorption peak. Additionally, the formation mechanism of the Bi4Ti3O12 nanoplates was also discussed.