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

doi:10.1016/j.jallcom.2013.08.181

Journal of Alloys and Compounds

Volume 583, 15 January 2014, Pages 198-205

https://doi.org/10.1016/j.jallcom.2013.08.181 Get rights and content

Highlights

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Sr_1−xPb_xBi₄Ti₄O₁₅ (SPBT, x = 0 − 0.4) ceramics were synthesized by soft chemical method.
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X-ray diffraction analysis confirmed the formation of bismuth layered structure.
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SEM images showed plate like grain morphology with random orientation of plate faces.
•
Pb-doping resulted in improved ferroelectricity of SrBi₄Ti₄O₁₅ ceramics.
•
Pb-doped SrBi₄Ti₄O₁₅ exhibited improved pyroelectric properties with high T_C.

Abstract

Ferroelectric properties of Pb-modified strontium bismuth titanate ceramics with chemical formula Sr₁₋_xPb_xBi₄Ti₄O₁₅ (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 (d₃₃) 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.

Graphical abstract

Introduction

The bismuth layer structured ferroelectric (BLSF) materials, due to their fatigue-free properties, have received significant attention for their application in non-volatile ferroelectric random access memory [1], [2], [3]. Compounds of this class possess relatively low-loss, low dielectric constant, higher resistance to aging and strong anisotropic electromechanical factors. In addition, these materials have higher ferroelectric ordering temperature and low temperature coefficient of resonance frequency, making them attractive for high temperature pyro- and piezoelectric applications [4], [5].

These compounds have pseudo-perovskite (A_m−1B_mO_3m+1)²⁻ blocks interleaved with an insulating (Bi₂O₂)²⁺ layers along the c-axis. In this formula, A represents mono-, di- and trivalent ions, or a mixture of them, B represents tetra-, penta- or hexavalent ions and m (=1, 2, 3…) is the BO₆ octahedra in the pseudo-perovskite block. The spontaneous polarization of BLSF arises from different modes of simultaneous rotation of oxygen octahedra. The displacements of ions in the perovskite B-sites contribute a major component of polarization in the a–b plane of the pseudo-perovskite layers. Among the BLSF compounds SrBi₂Ta₂O₉, Bi_3.25La_0.75Ti₃O₁₂ and SrBi₄Ti₄O₁₅ are the most promising candidates due to their good ferroelectric polarization and fatigue resistance up to 10¹² cycles [1], [3]. The fatigue-free property of these oxides is believed to originate from the insulating role of Bi₂O₂ layers as they are considered to be the compensation of space charges built-up near the electrode and/or suppression of ionic diffusion [6], [7]. In addition, these materials are believed to be chemically more stable structure than volatile Pb-containing oxides. The present work investigates the ferroelectric properties of modified SrBi₄Ti₄O₁₅ (SBT) ceramics.

SBT with m = 4 is a typical material that has been studied by many researchers for its piezoelectric and pyroelectric applications [8], [9], [10], [11], [12]. It crystallizes in orthorhombic structure with a space group A2₁am and has a b/a ratio of less than 1. The effect of doping at A- and B-sites of the lattice has shown some interesting changes on ferroelectric and pyroelectric properties of SBT. Zhao et al. [4] showed improved ferroelectric and pyroelectric properties in A- and B-site modified SBT ceramics. Similarly, Hirose et al. [10] showed that the La-modification in SBT ceramics resulted in the enhanced mechanical quality factor (Q_m) of 69.6, which is larger than that obtained for PbTiO₃ (19.1) ceramics. Recently, Rout et al. [12] synthesized fine grained SBT ceramics using the soft chemical method and studied the contribution of bulk and grain boundaries on electrical properties using impedance spectroscopy. In our earlier work, we reported interesting structural and magnetic properties of (Bi, La)FeO₃ modified SBT [13]. In the present work, we modified SBT with Pb (doping concentration up to 40 mol.%) to study the changes in its phase transitions and ferroelectric properties. It was shown that PbBi₄Ti₄O₁₅ (PBT), in spite of the presence of lead at A-site do not show any degradation in polarization even up to 10¹⁰ cycles [14]. Hence, it will be interesting to study the effect of chemically induced strain on its structure and physical properties, particularly the polarization. In order to avoid the volatility of Pb and Bi of the resulting compositions, the materials were synthesized via the modified sol–gel combustion method.

We observed an improved ferroelectric and pyroelectric properties in these ceramics along with an improved d₃₃∼22 pC/N for 40 mol.% Pb-doped SBT, against 18 pC/N for undoped SBT ceramics.

Section snippets

Experimental

Ceramic samples of Sr₁₋_xPb_xBi₄Ti₄O₁₅ with x = 0.0 (SBT), 0.1 (SPBT1), 0.2 (SPBT2), 0.3 (SPBT3) and 0.4 (SPBT4) were synthesized by modified sol–gel method. Starting raw materials for the synthesis were: high purity (Aldrich, 99.9%) strontium nitrate [Sr(NO₃)₂], bismuth nitrate pentahydrate [Bi(NO₃)₃·5H₂O], lead acetate and titanium dioxide [TiO₂, particle size < 50 nm]. Stoichiometric amounts of above nitrates were mixed in solution and TiO₂ was added to it, followed by stirring to yield an aqueous

Results and discussion

The X-ray patterns of the final sintered samples are shown in Fig. 1. All the peaks were indexed based on the reported data of SBT ceramics indicating the formation of single-phase compounds of Aurivillius phases with space group A2₁am [17], [18]. Some variations observed in the intensities and peak positions in XRD patterns can be attributed to the variations in lattice distortions of the samples. The lattice parameters calculated using the CHEKCELL program for SBT are a = 5.4505, b = 5.4391 and c =

Conclusion

4-layered SBT ceramics with Pb-modification were synthesized to study the effect of Pb modification on ferroelectric and pyroelectric properties. The change in chemical composition transformed the crystal structure and resulted in a higher tetragonal strain, which influenced the phase transitions. From the complex impedance spectroscopy it was observed that the Pb-doping has resulted in the improved grain boundary resistivity. The modification resulted in the improved pyroelectric activity with

Acknowledgements

The authors would like to acknowledge the financial support from FCT, Portugal (SFRH/BPD/75582/2010).

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

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusion

Acknowledgements

Mater. Sci. Eng. B

Curr. Opin. Solid State Mater. Sci.

J. Solid State Chem.

J. Alloys Comp.

J. Alloys Comp.

J. Solid State Chem.

J. Solid State Chem.

Solid State Commun.

Appl. Surf. Sci.

Mater. Sci. Eng. B

Sensors Actuators A

Mater. Res. Bull.

Nature

Adv. Mater.

Nature

Appl. Phys. Lett.

Appl. Phys. Lett.

J. Appl. Phys.

J. Am. Ceram. Soc.

Jpn. J. Appl. Phys.

Mater. Chem. Phys.

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