Dielectric and ferroelectric behavior of cerium modified SrBi2Ta2O9 ceramic

doi:10.1016/j.matlet.2015.06.093

Materials Letters

Volume 159, 15 November 2015, Pages 138-141

https://doi.org/10.1016/j.matlet.2015.06.093 Get rights and content

Highlights

•
Ce doped SrBi₂Ta₂O₉ ceramic has been prepared by solid state reaction route.
•
Dielectric constant and transition temperature decreases with Ce content.
•
Improvement on the ferroelectric behavior is obtained with Ce doping.

Abstract

Cerium modified bismuth layered ferroelectric SrBi₂Ta₂O₉ (SBT) with general formula SrBi_2−xCe_3x/4Ta₂O₉ (x=0, 0.025, 0.05, 0.075 and 0.1) is prepared by solid state reaction route. Structural and electrical properties of SrBi₂Ta₂O₉ ceramic are studied as a function of cerium content. The X-ray diffraction pattern indicates the formation of the single phase material for all compositions. The morphological study is done by Scanning electron microscopy, which shows plate like structure. The temperature dependent dielectric study shows a diffuse phase transition with a linear decrease in transition temperature and dielectric constant with an increase in Ce content. An increase in the dielectric diffuseness is obtained by an increase in Ce content. The ferroelectric property is studied by P–E hysteresis loop which shows a decrease in coercive field and increment in remanent polarization with an increase in Ce content.

Introduction

Aurivillius structured materials, the so-called bismuth layer structured ferroelectrics (BLSFs), have aroused much interest in the recent years due to their potential application in technical devices, e.g. in non-volatile ferroelectric random access memory (FE-RAM) [1], [2], [3], [4]. SrBi₂Ta₂O₉ ferroelectric has been extensively investigated as a promising candidate for nonvolatile ferroelectric random access memories, because of high fatigue endurance (up to 10¹¹ to 10¹² switching cycles), good retention characteristics, low switching fields, and low leakage current [5], [6], [7], [8]. It is widely accepted that the Bi₂O₂ layers have a significant influence on the polar and electrical conductivity properties of bismuth based layered structures. There has been a lot of research conducted to enhance their properties by the substitution of the Bi³⁺ ions of rare earth cations [9], [10], [11], [12], [13], [14]. The effect of CeO₂ on various ceramics has been extensively studied because of their high endurance under DC field stress, grain growth inhibition, and the effective Curie temperature shift. The valence states of cerium ions vary between trivalent (Ce³⁺) and tetravalent (Ce⁴⁺), depending on the starting formula and the sintering atmosphere [15]. Therefore, it is expected that by substituting Bi³⁺ ion with the large difference in the eightfold coordination ionic radii of Ce⁴⁺ ion in the crystal lattice of SBT ferroelectrics could enhance its physical properties. The effect of Ce doping on the structural, electrical and optical properties of SrBi_2−xCe_3x/4Ta₂O₉ (where x=0.00, 0.025, 0.05, 0.075 and 0.10) ferroelectric ceramics have been studied in detail.

Section snippets

Experimental procedure

SrCO₃, Bi₂O₃, CeO₂ and Ta₂O₅ are used as starting raw materials which are weighed according to the stoichiometric ratio with the formula SrBi_2−xCe_3x/4Ta₂O₉ (x=0, 0.025, 0.05, 0.075 and 0.1) and ground in an agate mortar for 2 h. The mixed powder is ball milled in a laboratory ball milling machine using Zr ball in acetone medium. 3 wt% of excess Bi₂O₃ is added with calculated precursors to compensate the loss during sintering. The mixed precursors are calcined at 1000 °C for 4 h after drying

Structural analysis

Fig. 1 shows the XRD pattern of Ce doped SrBi₂Ta₂O₉ ceramics calcinied at 1000 °C for 4 h. All the prominent peaks show the characteristic nature of single phase Bi-layered (m=2) Aurivillius compounds with A2₁am orthorhombic symmetry and are well agreed with the Joint Committee on Powder Diffraction Standards (JCPDS no 49-0609) card. The variation of lattice parameter is calculated by the MDI Jade5.0 program and shown in the inset of Fig. 1. The Ce⁴⁺ incorporation may change the type of bonding

Ferroelectric properties

The well saturated P–E hysteresis loop of Ce doped SrBi₂Ta₂O₉ ceramics at room temperature is shown in Fig. 4. It is observed that the P_r value increases and the E_c value decreases with increase in Ce content. Similar kind of improvement due to influence of rare-earth ion substitution in simple perovskite ferroelectrics have shown improved ferroelectric properties [19]. The substitution of rare earth in SBT produces oxygen vacancies with the ceramic. Oxygen vacancies produced by the replacement

Conclusion

Cerium modified SBT ceramic has been prepared by solid state reaction route. The XRD plot shows that the all the compositions are of single phase. A reduction in the grain size with a plate like structure is observed from the SEM figures. The temperature dependent dielectric study revealed that the dielectric constant and the transition temperature decreases with increase in Ce content. The diffusivity of dielectric maximum is found to increase with cerium content. The ferroelectric property is

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SrBi2Ta2O9 (SBTO) as a member of the Aurivillius family has a relatively negative conduction band (CB) position and the potential to reduce the organic pollutants. However, most works reported on SrBi2Ta2O9 mainly focus on their synthesis [23], thin-film [24], and ceramics [25]. The research is limited in visible-light-responsive photocatalysis application by its wide band gap and low overall efficiency [26].
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Multiferroic heterostructures thin films, SrBi₂Ta₂O₉/BaFe₁₂O₁₉ (SBT/BaM), were grown on Pt/TiO₂/SiO₂/Si substrates by using magnetron sputtering and Sol-gel ways. X-ray diffractometer (XRD) analysis showed that only SBT and BaM phases appeared in the multiferroic heterostructures. Magnetic hysteresis loops revealed that the saturated magnetization was 3.7 kG and the M-H characteristics of SBT/BaM were not influenced by the presence of the SBT layer. Ferromagnetic resonance (FMR) measurement showed the lowest FMR linewidth of 205 Oe at 50 GHz. Additionally, when direct-current electric field was applied to SBT layer, as a result of which mechanical deformation of the ferromagnetic layer occurred that leads to a frequency shift in ferromagnetic resonance and the magnetoelectric coupling effect (α) is 1.8 MHz*cm/kV. Our findings indicate that these SBT/BaM thin films have a significant potential for the usage in millimeter wave tunable devices.
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Relaxor ferroelectrics were discovered almost 50 years ago among the complex oxides with perovskite structure. In recent years, this field of research has experienced a revival of interest. The dielectric relaxation phenomenon in ferroelectric materials reflects the delay in the frequency response of a group of dipoles when submitted to an external applied field. Also, relaxor ferroelectrics show a high strain response and are actively being investigated for transducers and dielectric applications. The other promising field for relaxor applications is piezoelectric transducers and multilayer ceramic capacitors. This review presents properties and applications some of the most common relaxors such as PMN (Pb(Mg_1/3Nb_2/3)O₃, PLZT (Pb_1−xLa_x(Zr_1−yTi_y)_1−x/₄O₃), PZN (Pb(Zn_1/3Nb_2/3)O₃ and some less investigated such as Ba-based layered perovskites (BaBi₄Ti₄O₁₅, BaBi₂Ta₂O₉, and BaBi₂Nb₂O₉).
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Impedance spectroscopy and photocatalysis water splitting for hydrogen production with cerium modified SrBi<inf>2</inf>Ta<inf>2</inf>O<inf>9</inf> ferroelectrics
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Therefore, it would be important to examine new photocatalysts with Aurivillius-type structure. The dielectric and ferroelectric properties of cerium modified SBT ferroelectric ceramics is reported elsewhere [16]. In this paper, the SrBi2-xCe3x/4Ta2O9 compounds are synthesized by solid–state reaction method.
A pure phase cerium modified bismuth layer based Aurivillius type SrBi_2-xCe_3x/4Ta₂O₉ (x = 0–0.1) ferroelectric ceramics are synthesized by solid state route. X-ray diffraction patterns are well-indexed with orthorhombic (A₂₁am) according to the JCPDS card no. 49-0609. Impedance analysis revealed that the non-debye type nature and corresponding resistance-capacitance values are calculated. An existence of grain effect at high temperature is identified by modulus spectrum using Kohlrausch–Williams–Watts (KWW) function. The diffusive reflectance spectrum estimated the bandgap of cerium modified SrBi₂Ta₂O₉ ferroelectrics and the values are increased by increasing the substitution concentration. The conduction band of these photocatalysts composed of hybridization with Ta5d + Bi6p(Ce4f)+O2p orbitals and the valence bands composed of Ta5d + Bi6s(Ce4d)+O2p orbitals. The water splitting photocatalytic activity is investigated under UV-light irradiation and indicated that these photocatalysts showed photocatalytic activity for H₂ and O₂ evolution from aqueous solutions containing sacrificial reagents (methanol and Ag+). The correlation of electrical and photocatalytic properties are explained clearly.

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Dielectric and ferroelectric behavior of cerium modified SrBi2Ta2O9 ceramic

Highlights

Abstract

Introduction

Section snippets

Experimental procedure

Structural analysis

Ferroelectric properties

Conclusion

J. Alloy. Compd.

Mater. Lett.

Mater. Sci. Eng. B

Ceram. Int.

Ceram. Int.

Ceram. Int.

Fine-tolerance resonator applications of bismuth-layer-structured ferroelectric ceramics

Jpn. J. Appl. Phys.

Dielectric and ferroelectric properties of SrBi4Ti4O15 single-crystals

Appl. Phys. Lett.

Sintering and properties of molybdenum-doped SrBi2Ta2O9 ceramics Sintering and properties of molybdenum-doped SrBi2Ta2O9 ceramics

Eur. Ceram. Soc.

Dielectric and ferroelectric behavior of cerium modified SrBi₂Ta₂O₉ ceramic

Dielectric and ferroelectric properties of SrBi₄Ti₄O₁₅ single-crystals

Sintering and properties of molybdenum-doped SrBi₂Ta₂O₉ ceramics Sintering and properties of molybdenum-doped SrBi₂Ta₂O₉ ceramics