Elsevier

Ceramics International

Volume 43, Issue 7, May 2017, Pages 5367-5373
Ceramics International

Review article
Giant field-induced strain in Nb2O5-modified (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramics

https://doi.org/10.1016/j.ceramint.2017.01.084Get rights and content

Abstract

Lead-free piezoceramics (Na(1+x)/2Bi(1-x)/2)0.94Ba0.06Ti1-xNbxO3 (BTN100x) were prepared using conventional solid-state reaction method. The structures, field- induced strain, AC impedance of sintered ceramics were investigated. The pure perovskite solid solution BTN3 exhibited giant electric-field-induced strain of 0.478% under an electric field of 70 kV/cm at ambient temperature, meanwhile, the normalized strain (Smax/Emax) reached up to 654 pm/V. The giant strain was insensitive to temperature and exhibited excellent fatigue resistance performance within 106 switching cycles, making it a promising candidate material for actuator applications. Complex AC impedance spectra confirmed the contribution of grain effect to resistivity behavior. The field-induced giant strain was attributed to the phase transition between ferroelectrics and relaxor ferroelectrics induced by introducing Nb2O5.

Introduction

Materials based on piezoelectric effect are widely used in a variety of devices such as actuators, transducers, stress sensors, dielectric energy harvester, nano-positioners and imaging devices, etc [1], [2], [3]. Since 1950s, perovskite lead zirconate titanate (PbZrxTi1-xO3, abbreviated as PZT) based materials have been predominated the piezoelectric market for their excellent electromechanical and piezoelectric properties [4], [5], [6]. However, considering the environmental and health problems that lead may bring during the procession of manufacturing and practical usage, many countries and international organizations have legislated series of laws and regulations to eliminate or eradicate the use of lead [7], [8], [9]. Hence, much attention has been attracted to fabricate the lead-free candidate for PZT-based piezoceramics and several lead-free systems have been developed.

Among the lead-free perovskite families, sodium bismuth titanate (Na0.5Bi0.5TiO3, abbreviated as BNT) based material is considered to be the most promising candidate [10].

Pure BNT exhibits typical ferroelectric properties, which undergoes a relaxed phase transition at ~200 °C, but its large coercive field and relatively inferior properties make it difficult to be put into practical use. Significant improvements are normally achieved in BNT-based binary or ternary systems, such as Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3 (BNT-BKT), Na0.5Bi0.5TiO3-BaTiO3 (BNT-BT, or BNBT) and Na0.5Bi0.5TiO3-BaTiO3-K0.5Na0.5NO3 (BNT-BT-KNN) [11], [12], [13], yet lead-free counterparts still cannot compete with lead-based ones [4]. Among the BNT-based solid solutions, BNT-xBT has received the most impressive attention due to its excellent properties near the morphotropic phase boundary (MPB) with x=0.06–0.07 [14], [15]. Researchers obtained giant strain and excellent piezoelectric properties near the MPB structure by chemical modification. Liu et al. [12] reported an ultra-high strain of 0.7% (Smax/Emax=1400 pm/V) in non-textured BNT-based lead-free ceramics. Cheng et al. [16] studied a large field-induced-strain of 0.442% (Smax/Emax=844 pm/V) in Fe3+/Nb5+ co-doped (Bi0.5Na0.5)0.935Ba0.065Ba0.065TiO3 piezoceramics. Summarized from previous reports, it is an effective way to obtain large strain by adjusting phase transition temperature of relaxor ferroelectric to ambient temperature [17], [18], as to say a “relaxor ferroelectric+ferroelectric” phase in solid solutions contribute to a high field-induced strain.

In this work, Nb2O5 was doped into modified BNT-BT binary system to induce the relaxor phase transition under ambient temperature. The electric-field-induced strain, ferroelectric, dielectric properties and AC impedance were studied to highlight the effect of Nb2O5 substitution.

Section snippets

Experiment processing

The (Na(1+x)/2Bi(1-x)/2)0.94Ba0.06Ti1-xNbxO3 (BTN100x, x=0, 0.01, 0.03, 0.05, 0.07) ceramics were prepared using a traditional solid-state reaction technique. Raw powders of Bi2O3 (99.9%), Na2CO3 (99.5%), BaCO3 (99.9%), TiO2 (98%), and Nb2O5 (99.99%) were weighted according to stoichiometric quantities. Firstly, the raw powders were mixed and ball-milled in polyethylene pots with zirconia balls for 16 h,while the anhydrous ethanol performed as ball-milling media, then the slurry were dried.

Phase and microstructure analysis

Fig. 1(a) shows XRD patterns of sintered BTN100x ceramics recorded at room temperature with 2θ=20°−75°. All the samples exhibit pure perovskite structure without any trace of secondary phases, implying the dopant Nb2O5 have diffused into the crystal lattice and formed stable solid solutions with BNBT. Fig. 1(b) shows the expanded XRD patterns with 2θ ranging from 46.2 to 47°. The position of non-spilt peaks of (200) shift slightly to lower angle with increasing Nb2O5 content, suggesting a

Conclusions

A series of (Na(1+x)/2Bi(1-x)/2)0.94Ba0.06Ti1-xNbxO3 ceramics were fabricated by conventional solid-state reaction method. XRD patterns implied the dopant Nb2O5 have diffused into the crystal lattice and formed stable solid solutions with BNBT. High electric field induced strain of 0.478% was obtained at BTN3, meanwhile the corresponding normalized strain run up to 654 pm/V. The strain retained at a high level above 0.34% from room temperature to 100 °C. The broadened dielectric curves and

Acknowledgements

This work is supported by the National Nature Science Foundation (51172187), the SPDRF (20116102130002), the 111 Program (B08040) of MOE, the Xi’an Science and Technology Foundation (XBCL-1-08), the SKLP Foundation (KP201421, KP201523, SKLSP201409), the Project of Key Areas of Innovation team in Shaanxi Province (2014KCT-12), the Fundamental Research Funds for the Central Universities (3102014JGL01002).

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