Bismuth-layered Structure Research Articles

Effect of CuO addition on magnetic and electrical properties of Sr2Bi4Ti5O18 lead-free ferroelectric ceramics

The effect of CuO addition on magnetic and electrical properties of Sr2Bi4Ti5O18 (SBT) lead-free bismuth layered structure ferroelectric ceramics have been studied and reported. Interestingly, the prepared samples exhibit multiferroic behavior with the coexistence of magnetic and ferroelectric phase transition temperature. Magnetic phase transition with Neel׳s temperature (TN) of 657K is observed at 0.75mol% of CuO added SBT ceramics, which is higher than the well known multiferroic BiFeO3 (643K) and the ferroelectric phase transition with Curie temperature (TC) of 587K is observed at 1mol% of CuO added SBT ceramics, which is relatively higher than the reported pure SBT ceramics (558K). Further, the electrical properties such as dielectric, ferroelectric, piezoelectric, leakage current density characteristics and optical properties were investigated as a function of x (x=0, 0.25, 0.5, 0.75 and 1mol%). Presence of strong magnetic super-exchange interactions in CuO and the creation of oxygen vacancies play a vital role in the enhancement of magnetic and electrical properties of CuO doped SBT ceramics. Moreover, the present results indicate that, small amount (0.25mol%) of CuO addition in SBT ceramics enhances the electrical properties significantly and vice versa, large amount (0.75mol%) of CuO addition enhances the magnetic properties. Thus, the presence of magneto-electric coupling effect was observed in CuO doped Sr2Bi4Ti5O18 ferroelectric ceramics.

Modified Lorentz and Gauss Equations to Describe the Dielectric Behaviour of Sr1-2xNaxNdxBi4Ti4O15 Normal Ferroelectric Compounds

Modified Lorentz and Gauss equation is proposed to describe the temperature dependence of dielectric constant for bismuth layered structure ferroelectric materials i.e. Sr1-2xNaxNdxBi4Ti4O15. The validity of the proposed equation was checked from the regression value obtained. The activation energy for orientation of dipoles, static dielectric constant and infinite dielectric constant obtained from the non linear curve fitting to experimental data by using modified Lorentz and Gauss equation have reasonable values. Modified Lorentz equation is found to be the best fit to the experimental dielectric data. The above modified equations may also be used to describe the dielectric behaviour of other normal ferroelectric materials which show sharp transitions.

ELECTRICAL MEASUREMENT OF LA MODIFIED BI4TI3O12 FRAM CERAMIC

Bismuth Layer Structured Ferroelectric (BLSF) ceramic of La0.75Bi3.25Ti3O12, (BLT) abbreviated as future promising ferroelectric random access memory materials was prepared by the conventional solid-state reaction method. Resistivity and dielectric measurements were made as a function of temperature and frequency. The remnant polarization (Pr) is found to be 16 C/cm 2 . The ferroelectric results were corroborated with the electrical impedance, resistivity and hysteresis properties

Structure, Ferroelectric and Photoluminescence Properties of Eu-Doped CaBi4Ti4O15 Multifunctional Ceramics

Lead-free multifunctional ceramics of CaBi4−xEuxTi4O15 were prepared by a traditional solid state method, and the effects of Eu doping on structure, ferroelectric, piezoelectric and photoluminescence properties of the ceramics were investigated. All the ceramics possessed typical bismuth layer structure with m = 4, belonging to orthorhombic symmetry, and no secondary phase was detected. The plate-like grains were observed in all the ceramics, and the grain growth was slightly inhibited after the addition of Eu. Saturated polarization hysteresis loops were observed for all the ceramics, and the remanent polarization Pr decreased with Eu doping. The Eu-doped ceramics had a sharp excitation band centered at 465 nm due to the f–f transition from the 7F0 ground state to the 5D2 excited state of Eu3+. Under the excitation by 465 nm light, the main emission peaks located at 595 nm and 616 nm were obtained, which corresponds to the transition of 5D0–7F1, 5D0–7F2 levels in Eu3+, respectively. Our study shows that CaBi4Ti4O15 ceramics may be a promising multifunctional material for potential applications in optical-electro integration devices.

Enhanced piezoelectric properties of Nb and Mn co-doped CaBi4Ti4O15 high temperature piezoceramics

The properties of CaBi4Ti4O15 (CBT), CaBi4Ti3.95Nb0.05O15 (CBTN) and CaBi4Ti3.95Nb0.05O15+0.2wt% MnO2 (CBTN–Mn) ferroelectric ceramics with bismuth layer structure were studied. Significant enhancement of piezoelectric coefficient was obtained for CBTN–Mn ceramics (d33=23pC/N), being nearly three times that of CBT counterpart (d33=8pC/N). Together with its high Curie temperature (Tc=790°C), low dielectric loss (tanδ=0.2%), high resistivity (ρ=4.2×106Ωcm at 500°C) and good thermal stability up to 700°C, the CBTN–Mn ceramic is a potential material for high temperature piezoelectric applications.

Ferroelectric Properties and Microstructures of Bi4-xDyxTi3O12 Thin Films

Dy-doped Bi4Ti3O12 thin films were fabricated on Pt/Ti/SiO2/Si substrates by pulsed laser deposition technique, and the structures and electrical properties of the films were investigated. XRD results indicated that all of Bi4-xDyxTi3O12 films consisted of single phase of a bismuth-layered structure with well-developed rod-like grains. The remanent polarization ( Pr ) and coercive field (Ec) of the Bi4-xDyxTi3O12 Film with x=0.75 were 25μC/cm2 and 85KV/cm , respectively.

Electrical Characteristics and Microstructures of Pr<sub>2</sub>O<sub>3</sub>-Doped Bi<sub>4</sub>Ti<sub>3</sub>O<sub>12</sub> Thin Films

Pr2O3-doped bismuth titanate (Bi4-xPrxTi3O12: BPT) thin films with random oriention were fabricated on Pt/Ti/SiO2/Si substrates by rf magnetron sputtering technique, and the structures and ferroelectric properties of the films were investigated. XRD studies indicated that all of BPT films consisted of single phase of a bismuth-layered structure with well-developed rod-like grains. For samples with x=0..0 , 0.25, 1.0 and 1.25, I-E characteristics exhibited negative differential resistance behaviors and their ferroelectric hysteresis loops were characterized by large leakage current, whereas for samples with x=0.5 and 0.75, I-E characteristics were simple ohmic behaviors and their ferroelectric hysteresis loops were the saturated and undistorted hysteresis loops. The remanent polarization ( Pr ) and coercive field (Ec) of the BPT Film with x=0.75 were above 30μC/cm2 and 75KV/cm , respectively.

Dielectric and ferroelectric properties of SrBi4Ti4O15–Sr2Bi4Ti5O18 composite ceramics

The bismuth layered structure ferroelectric ceramic composite between SrBi4Ti4O15 and Sr2Bi4Ti5O18 was synthesized through modified oxalate route. Phase formation behaviour of each compound in the composite was studied. The XRD analysis revealed the growth of two separate phases without forming any periodic intergrowth structure between them. The Rietveld structure refinement disclosed an increase in the lattice parameter of both phases. The densification behaviour of the composite powder was investigated using dilatometer. There was a preferential orientation in growth of plate like grains during sintering. The composite ceramic showed an additional dielectric anomaly peak in between the peaks for SrBi4Ti4O15 and Sr2Bi4Ti5O18 phases. The ferroelectric hysteresis property of the composite ceramics represented an average behaviour of two phases.

Variation In Mechanical Properties With Substrate Temperature Of SbTi Thin Film Deposited By RF Sputtering Technique

Nanoindentation technique has been used to determine the mechanical properties of bismuth layered structure ferroelectric thin films, which have been shown to be promising for MEMS based devices used in sensing, actuation and energy harvesting, especially at elevated temperatures. SBTi (SrBi4Ti4O15) is a promising layered ferroelectric material and thin films of this composition are deposited on amorphous fused silica substrates by rf sputtering technique varying the substrate temperature from 600–725 o C. The crystal structure and surface morphology of SBTi thin films are characterized by X-ray diffraction and atomic force microscopy. Depth- sensing nanoindentation system is used to measure the mechanical characteristics of SBTi thin films. Nanoindentation measurements reveal that the Young’s modulus and hardness of SBTi thin films are related with grain size and crystal orientation which in turn depend on substrate temperature. The increase in mechanical properties with grain size is observed, indicating the reverse Hall-Petch effect. Furthermore, hardness and Young’s modulus of the (119) oriented films were higher than those of (0010) oriented films. The tribological properties of these films are confirmed by performing the scratch tests on the same films.

Phase Competition in Bismuth Layered Structure Based on First Principles Thermodynamics

The difficulties of synthesis of pure Aurivillius phases largely impede them from extensive application. In this work, the first principles thermodynamics approach was applied to investigate the phase competition relation of three homologous Aurivillius series CaBi2Nb2O9-nNaNbO(3), Bi4Ti3O12-nSrTiO(3) and Bi4Ti3O12-nCaTiO(3), in order to uncover the thermodynamic mechanism of the phase stability. The competition among different phases was analyzed by the relative Gibbs energy as a function of chemical potential of perovskite unit. The analysis reveals that most phases are able to overcome others to be the most stable ones in a certain range as chemical potential increases, which can be applied to interpret the relevant experimental phenomena including the phase mixture and disordered structures. Temperature dependence of phase competition evolutions are also studied based on the configurational and vibrational entropy effect, the former effect changes the competition relations of different phases, while the latter only increases the stable range of the lower phases.

Improved ferroelectric and pyroelectric properties of Pb-doped SrBi4Ti4O15 ceramics for high temperature applications

• Sr 1−x Pb x Bi 4 Ti 4 O 15 (SPBT, x = 0 − 0.4) ceramics were synthesized by soft chemical method. • X-ray diffraction analysis confirmed the formation of bismuth layered structure. • SEM images showed plate like grain morphology with random orientation of plate faces. • Pb-doping resulted in improved ferroelectricity of SrBi 4 Ti 4 O 15 ceramics. • Pb-doped SrBi 4 Ti 4 O 15 exhibited improved pyroelectric properties with high T C . Ferroelectric properties of Pb-modified strontium bismuth titanate ceramics with chemical formula Sr 1− x Pb x Bi 4 Ti 4 O 15 ( x = 0–0.4) were investigated. Polycrystalline ceramics were synthesized by soft chemical method to study the effect of Pb-doping on its physical properties. X-ray diffraction analysis revealed a bismuth layered structure for all the compounds. The doping resulted in an increased tetragonal strain and improved ferroelectric properties. Scanning electron microscope images showed plate like grain morphology with random orientation of platelets. The ferroelectric transition temperature of the ceramics increased systematically from 525 °C to 560 °C with the increase of doping concentration. The piezoelectric coefficient ( d 33 ) of the ceramics was enhanced significantly with Pb doping, exhibiting a maximum value of 21.8 pC/N for 40 mol.% Pb-doped SBT. Pyroelectric studies carried out using the Byer–Roundy method indicated that the modified SBT ceramics are promising candidates for high temperature pyroelectric applications.

Fabrication and Piezoelectric Property of Textured Bismuth Layered Structure Ceramics by Hot Pressing Technique

The bismuth layered structure materials (BLSFs) with general formula of the (Bi2O2)2+(Am-1BmO3m+1)2-, have attracted considerable attention for high-temperature piezoelectric applications. Hot pressing is a useful densifying and texture technique for enhancing the piezoelectric properties. In this present study, four different types (m=1, 2, 3, 4) of ceramics with Aurivillius structure were prepared and the influential factors of textured degree was investigated systematically by hot pressing method. The result indicates that the value of m is larger, the BLSFs ceramics is easier to get high degree of texture and high piezoelectric properties in the parallel of the hot pressing direction.

Effects of (Ca,Sb) on the Properties of Na0.5Bi2.5Nb2O9-based Bismuth Layered Structure Ferroelectric Ceramics

Dense Na0.5Bi2.5Nb2O9 (NBN) based high temperature piezoelectric ceramics were prepared by solid-state reaction method. The effects of Ca2+ and/or Sb5+ in NBN pseudo-perovskite structure A and/or B site were studied. The introduction of Sb5+ into B site decreases Curie temperature T c and piezoelectric constant d 33, while Ca2+ into A site increases T c and d 33. Within the selected compositional range, the incorporation of Ca2+ and Sb5+ into A, B site, respectively, increased d 33 compared to NBN. The optimum content of Ca2+ and Sb5+ are 3.0 mol%, 1.0 mol%, respectively, of which, the piezoelectric constant d 33 is about 18.1 pC/N, T c is about 790°C.

Ferroelectric and Electrical Behavior of Bi<sub>4-x</sub>Nd<sub>x</sub>Ti<sub>3</sub>O<sub>12</sub> Thin Films

Nd2O3-doped bismuth titanate (Bi4-xNdxTi3O12: BNT) thin films with random oriention were fabricated on Pt/Ti/SiO2/Si substrates by rf magnetron sputtering technique, and the structures and ferroelectric properties of the films were investigated. XRD studies indicated that all of BNT films consisted of single phase of a bismuth-layered structure with well-developed rod-like grains. The remanent polarization ( Pr ) and coercive field (Ec) of the BNT Film with x=0.8 were 25μC/cm2 and 55KV/cm , respectively. After 3×1010 switching cycles, 15% degradation of Pr is observed in the film.

Effects of Sputtering Conditions on Microstructure and Ferroelectric Properties of RF-Sputtered Bi<sub>3.25</sub>La<sub>0.75</sub>Ti<sub>3</sub>O<sub>12</sub> Thin Films

The Bi3.25La0.75O12 films were prepared on the Pt/TiO2/SiO2/Si substrate using RF-magnetron sputtering method. The effects of sputtering conditions, including sputtering pressure, oxygen partial pressure and substrate temperature on microstructure, ferroelectric properties were investigated. When deposited at low substrate temperature (room temperature), the BLT thin film exhibits preferentially c-axis oriented. With the increasing of substrate temperature, the (117) diffraction peak become stronger, indicating the changing of the microstructure in the BLT films. The BLT film samples deposited at 4.5-6Pa exhibit desired bismuth-layered structure, with no any preferred orientation. However, when BLT films were deposited above 5 Pa, some weak pyrochlore diffraction peaks appear in the X-ray diffraction pattern. The Pr is a maximum for the BLT film deposited at 5 Pa with O2/Ar ratio 1/5 and decreases with both decreasing and increasing deposition pressure.

Study on A-site Cation Doping of CaBi<SUB>2</SUB>Nb<SUB>2</SUB>O<SUB>9</SUB> with Bismuth Layered Structure

利用固相反应法合成了Ca 1- x (KLa) x /2 Bi 2 Nb 2 O 9 ( x =0~0.20)( x KLaCBNO)铋层状陶瓷, 分析不同KLa掺杂量对CaBi 2 Nb 2 O 9 (CBNO)基陶瓷微观结构、介电、压电及电导性能的影响. XRD分析表明KLa的引入未改变CBNO陶瓷的单相结构. SEM和介电系数温度谱结果分别显示, KLa掺杂量的增加, 细化尺寸趋于一致, 而居里温度( T c )从943℃降低至875℃, 其峰值介电常数减小、峰值介电损耗增大. 当掺杂量 x =0.1时, 样品的高温电阻率较纯CBNO显著升高, 压电系数 d 33 由5.2 pC/N提高到15.8 pC/N, 居里温度高达870℃, 说明A位(KLa)掺杂改性后的CBNO陶瓷在高温传感器等领域具有潜在的应用前景.

Raman scattering, microstructural and dielectric studies on Ba1−xCaxBi4Ti4O15 ceramics

Polycrystalline powders of Ba1−xCaxBi4Ti4O15 (where x = 0, 0.25, 0.50, 0.75 and 1) were prepared via the conventional solid-state reaction route. X-ray diffraction (XRD) and Raman scattering techniques have been employed to probe into the structural changes on changing x. XRD analyses confirmed the formation of monophasic bismuth layered structure of all the above compositions with an increase in orthorhombic distortion with increase in x. Raman spectra revealed a redshift in A1g peak and an increase in the B2g/B3g splitting with increasing Ca content. The average grain size was found to increase with increasing x. The temperature of the maximum dielectric constant (Tm) increased linearly with increasing Ca-content whereas the diffuseness of the phase transition was found to decrease with the end member CaBi4Ti4O15 showing a frequency independent sharp phase transition around 1048 K. Ca doping resulted in a decrease in the remnant polarization and an increase in the coercive field. Ba0.75Ca0.25Bi4Ti4O15 ceramics showed an enhanced piezoelectric coefficient d33 of 15 pC N−1 at room temperature. Low values of dielectric losses and tunability of temperature coefficient of dielectric constant (τɛ) in the present solid-solution suggest that these compounds can be of potential use in microwave dielectrics at high temperatures.

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.

Ferroelectric Properties and Microstructures of Tb<sub>4</sub>O<sub>7</sub>-Doped Bi<sub>4</sub>Ti<sub>3</sub>O<sub>12</sub> Thin Films

Tb-doped bismuth titanate (BixTbyTi3O12 BTT) thin films were fabricated on Pt/Ti/SiO2/Si substrates by rf magnetron sputtering technique, and the microstructures and ferroelectric properties of the films were investigated. Microstructure studies indicate that all of BTT films with well-developed rod-like grains consist of single phase of a bismuth-layered structure without preferred orientation. The experimental results indicate that Tb doping into Bi4Ti3O12 results in a remarkable improvement in ferroelectric properties. The remanent polarization ( Pr ) and coercive field ( Ec ) of the BTT film with y=0.6 were 22 μC/cm2 and 85 kV/cm, respectively. After 3 × 1010 switching cycles, 20% degradation of Pr is observed in the film.

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.