Structure, ferroelectric and piezoelectric properties of multiferroic Bi0.875Sm0.125FeO3 ceramics

doi:10.1016/j.jallcom.2012.06.094

Journal of Alloys and Compounds

Volume 541, 15 November 2012, Pages 173-176

https://doi.org/10.1016/j.jallcom.2012.06.094 Get rights and content

Abstract

With a rhombohedra-like structure, the Bi_0.875Sm_0.125FeO₃ ceramics show much-improved ferroelectric and piezoelectric properties: a saturated ferroelectric polarization of 40 μC/cm² and a piezoelectric d₃₃ of 45 pC/N at 20 °C. After the polarized sample was annealed at 600 °C, its d₃₃ decreases to ∼20 pC/N. Besides, Bi_0.875Sm_0.125FeO₃ shows dielectric or impedance resonances at 20–550 °C, suggesting that the ferroelectric component with high Curie temperature still partially remained at 550 °C. However, the impedance and the resistance decrease so fast with temperature increasing that both of them are below 1000 ohm above 420 °C. Even so, this piezoelectric resonance method can explore leaky ferroelectrics at high temperature.

Highlights

► Piezoelectric responses were observed at 20–550 °C in Bi_0.875Sm_0.125FeO₃. ► Ferroelectric component partially remained at 700 °C. ► Both impedance and resistance were smaller than 1000 ohm above 420 °C.

Introduction

Although the outstanding piezoelectric properties of Pb₁₋_xZr_xTiO₃ (PZT) ceramics have drawn extensive attention, their lead content is currently facing global restrictions due to its toxicity. Thus, there is an urgent need to develop such a non-Pb substitute as Bi₁₋_xSm_xFeO₃ [1] to make up for this weakness. Pb-free BiFeO₃ with rhombohedral R3c structure has ferroelectric order below Curie temperature (T_C−FE) of ∼800 °C and G-type canted anti-ferromagnetic order below Neel temperature (T_N−AFM) of ∼370 °C [2], [3], [4]. Recently, Zeches et al. have reported that the strain-driven epitaxial BiFeO₃ film on (1 1 0) YAlO₃ substrate exhibited a large piezoelectric d₃₃ of ∼120 pm/V and a reversible electric-field-induced strain of over 5% [5]. Besides, the Bi_0.84Sm_0.16FeO₃ epitaxial film also allows an enhanced d₃₃ of ∼120 pm/V at 500 kV/cm, because the Sm³⁺ ion with a smaller radius of 0.958 Å partially replaces Bi³⁺ ion with a radius of 1.030 Å [6], [7]. It is reported that Bi₁₋_xSm_xFeO₃ films change from rhombohedral R3c phase to PbZrO₃-like anti-ferroelectric orthorhombic Pbam phase at x ∼ 0.12 and finally to SmFeO₃-like paraelectric orthorhombic Pnma phase at higher x [6], [7]. These results demonstrate the potential of Bi₁₋_xSm_xFeO₃ family as a substitute for lead-based materials in future piezoelectric applications.

First, it is necessary to study the dependence of electric properties of Bi₁₋_xSm_xFeO₃ ceramics on temperature. BiFeO₃ with rhombohedral R3c phase commonly keep higher T_C−FE [4], however it is not clear whether Bi₁₋_xSm_xFeO₃ can be used as high-temperature piezoelectric materials. As is known, bismuth layered high-temperature piezoelectric materials own wider band gap to allow higher resistivity at high temperature. For example, the CaBi₄Ti₄O₁₅ with T_C−FE of 790 °C permits room-temperature d₃₃ of 14 pC/N and 10⁷ ohm cm at 500 °C [8]. On the contrary, BiFeO₃ with the band gap of ∼2.8 eV usually changes from a room-temperature ferroelectric insulator to a conductor when above 400 °C due to electron thermal excitation. As a result, it’s difficult to apply a high electrical field larger than coercive field (E_C) to leaky ceramics to polarize them before large leakage current breaks down samples at high temperature. Despite this, it is still valuable to study piezoelectric properties of leaky Bi₁₋_xSm_xFeO₃ at high temperature.

Although extensive researches, especially magnetic properties, have been down in doped BiFeO₃ ceramics [1], [2], [3], [4], [9], [10], there are few reports on piezoelectric properties of Bi₁₋_xSm_xFeO₃ ceramics at high temperature. Piezoelectric ceramics can be applied in many sensors, actuators and so on, which cannot be replaced by the devices with films, and furthermore, their crystal structure, ferroelectric and piezoelectric properties may be different from the corresponding epitaxial films in many cases. Therefore, Bi₁₋_xSm_xFeO₃ ceramics should be studied systematically.

Here we prepare Bi_0.875Sm_0.125FeO₃ ceramics and then prove that their piezoelectric responses can be observed up to 600 °C though the ceramics have already become seriously leaky and the ferroelectric component only survived partially.

Section snippets

Experimental details

A rapid liquid-phase sintering method with a high heating rate of ∼100 °C/s was applied to prepare single-phase Bi_0.875Sm_0.125FeO₃ ceramics [4]. High-purity 99.95% oxide powders were weighed according to the nominal compositions of Bi_0.875Sm_0.125FeO₃. Each type of powder was finely milled into sizes of <1 μm. After being dried, the powders were mixed thoroughly with water and pressed into disks with 0.8 mm thickness [4]. Then, these disks were dehydrated at 400 °C for 10 h before being sintered at a

Results and discussion

The XRD patterns of Bi_0.95Sm_0.05FeO₃, Bi_0.875Sm_0.125FeO₃ and Bi_0.85Sm_0.15FeO₃ are shown in Fig. 1. The XRD patterns of Bi_0.95Sm_0.05FeO₃ and Bi_0.875Sm_0.125FeO₃ agree well with a triclinic structure (i.e., a = 3.9550/3.9400 Å, b = 3.9466/3.9344 Å, c = 3.9481/3.9132 Å, α = 89.500/89.549°, β = 89.500/89.554° and γ = 89.500/89.616°, respectively) in Fig. 1a. This suggests that Bi_0.875Sm_0.125FeO₃, like BiFeO₃ and Bi_0.95Sm_0.05FeO₃ bulk, owns a rhombohedra-like structure with little triclinic distortion (Fig. 1b),

Conclusions

The Bi_0.875Sm_0.125FeO₃ ceramic with rhombohedral R3c structure has a ferroelectric polarization of 40 μC/cm² at room-temperature. The as-polarized ceramics show an enhanced piezoelectric d₃₃ of 45 pC/cm at 20 °C, however, it decreases to 20 pC/N after the ceramic was annealed at 600 °C. This suggests the existence of ferroelectric component with high Curie temperature. Both piezoelectric thickness resonance and planar resonance contribute to capacitance peaks and impedance peaks at ⩽550 °C,

Acknowledgments

This work was supported by the National Key Project for Basic Research of China (2012CB619406), the National Natural Science Foundation of China (11134004 and 51072081) and the Natural Science Foundation of Jiangsu Province (SBK201123822).

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Citation Excerpt :
This may be attributed to the suppression of Bi evaporation and charge defects (oxygen vacancies or bismuth vacancies) [45]. The bond enthalpies of Sm-O and Nb-O bonds are higher than those of Bi-O and Fe-O bonds, and thus doping Sm at Bi-sites and Nb at Fe-sites can stabilize the perovskite structure and reduce the volatilization of Bi [15,20]. Furthermore, doping high valence Nb5+ for Fe3+ could fill the oxygen vacancies.
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Structure, ferroelectric and piezoelectric properties of multiferroic Bi0.875Sm0.125FeO3 ceramics

Abstract

Highlights

Introduction

Section snippets

Experimental details

Results and discussion

Conclusions

Acknowledgments

J. Alloys Compd.

J. Alloys Compd.

Solid State Commun.

J. Alloys Compd.

J. Alloys Compd.

Solid State Commun.

Appl. Phys. Lett.

J. Appl. Phys.

Science

Structure, ferroelectric and piezoelectric properties of multiferroic Bi_0.875Sm_0.125FeO₃ ceramics