Ferroelectric and pyroelectric properties of (Na0.5Bi0.5)TiO3–BaTiO3 based trilayered thin films
Introduction
At present, lead zirconate titanate [Pb(Zr,Ti)O3)] is the most popular ferroelectric film due to its excellent piezoelectric and pyroelectric properties. However, the toxicity of lead oxide and its high vapor pressure during processing have led to a demand for alternative lead-free piezoelectric materials or piezoelectric materials with little lead content. (Na0.5Bi0.5)xBa1 − xTiO3 is considered as a promising candidate [1], [2], [3], [4]. The ferroelectric and piezoelectric properties of (Na0.5Bi0.5)xBa1 − xTiO3 in bulk form have been extensively studied. It was reported that the bulk form of (Na0.5Bi0.5)xBa1 − xTiO3 with a composition near morphotropic phase boundary (MPB) (x = 0.06–0.07) shows best ferroelectric and piezoelectric properties [1]. The piezoelectric constant of the (Na0.5Bi0.5)xBa1 − xTiO3 ceramics with the MPB composition can reach up to 125 pC/N [1], the (100)-oriented crystals grown by spontaneous nucleation method showed a piezoelectric constant of d33 = 450 pC/N and an electric field induced strain up to 0.25% [3].Meanwhile, good pyroelectric properties (pyroelectric coefficient Pi = 3.9 × 10− 4 C m− 2 K− 1) for MPB composition have also been achieved [5], which possibly result from the large spontaneous and remnant polarization (Pr = 40 µC/cm2) and lower depolarization temperature (Td = 100 °C) of this material [1]. However, (Na0.5Bi0.5)xBa1 − xTiO3 in thin film form was few investigated. Very recently, Scarisoreanu et al. have reported the deposition of (Na0.5Bi0.5)xBa1 − xTiO3 films by pulse laser deposition [6]. The films have a relatively high dielectric constant but very weak ferroelectricity due to a very low effective breakdown field. In our previous study, we prepared highly (100)-oriented (Na0.5Bi0.5)0.94Ba0.06TiO3 (NBT-BT) thin films on the LaNiO3 electrodes by a chemical solution deposition [7]. The films show good dielectric properties but we also found that the saturated hysteresis loops are still difficult to obtain due to relatively high leakage currents under high electric fields. Therefore, it is very important to improve the insulating properties of NBT-BT films.
Here, we propose that the multilayer films are an alternative effective structure to ensure the film having a good insulating characteristic against applied field. In the last few years a great interest has been developed in the heterogeneous multilayer thin films having successive layer of different compositions, due to their artificially enhanced dielectric, ferroelectric and pyroelectric properties [8], [9], [10], [11], [12], [13], [14], [15], [16]. It was reported that the formation of artificially layered structures offers opportunities to tailor the electrical properties of the ferroelectric materials. Recently, some experimental efforts have been devoted to the fabrication of ferroelectric multilayered films or superlattices, mostly for improving the dielectric properties. It is shown that multilayered dielectric films such as BaTiO3/SrTiO3, PbTiO3/PbZrO3, PbTiO3/BaTiO3, SrBi2Ta2O9/SrBi2Nb2O9 have dielectric and ferroelectric properties much different from their parent phases [8], [9], [10], [11], [12], [13], [14], [15], [16]. However, the influence of multilayers on the insulating properties was few studied. In this paper, two kind of trilayered Bi3.25La0.75Ti3O12 (BLT)/NBT-BT/BLT and Pb(Zr0.4Ti0.6)O3 (PZT)/NBT-BT/PZT thin films were prepared by a chemical solution deposition. Their structure, dielectric, ferroelectric and pyroelectric properties were investigated.
Section snippets
Experimental details
NBT-BT precursor solutions were prepared by using barium acetate (Ba(CH3COO)2), bismuth nitrate (Bi(NO3)3.5H2O), and titanium isopropoxide (Ti[OCH(CH3)2]4 as starting materials. 2-methoxyethanol and acetic acid were chosen as co-solvent. Acetylacetone (CH3COCH2COCH3) and ethanolamine (H2NCH2CH2OH) were chosen as ligands. The detailed synthesis process was described in our previous study [7]. BLT and PZT were synthesized as those of references [17], [18], respectively. All the synthesis process
Results and discussions
Fig. 1, Fig. 2 show the XRD patterns of trilayered BLT/NBT-BT/BLT and PZT/NBT-BT/PZT thin films on Pt (111)/Ti/SiO2/Si (100) substrates. Only series of NBT-BT, PZT or BLT peaks were observed, indicating there are no second phases in the obtained films within the sensitivity of X-ray diffraction. In trilayered BLT/NBT-BT/BLT films (Fig. 1), the BLT films show (117) preferred as their single phase BLT films and the NBT-BT films show (110) preferred orientation. In trilayered PZT/NBT-BT/PZT films (
Conclusions
Trilayered BLT/NBT/BLT and PZT/NBT/PZT thin films without second phases have been deposited on Pt/Ti/SiO2/Si substrates by a chemical solution deposition. Much better insulating properties in the trilayered films show that the BLT and PZT layers are very effective to inhibit the charge transport. Good dielectric properties were obtained for the trilayered films. Enhanced ferroelectric and pyroelectric properties were observed in the trilayered films. Remnant polarization 2Pr of 16 µC/cm2 and
Acknowledgements
This work was supported by the Pujiang scholar foundation of Shanghai (No. 08PJ1407100) and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.
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