Effect of neodymium substitution on crystalline orientation, microstructure and electric properties of sol-gel derived PZT thin films

doi:10.1016/j.ceramint.2018.01.197

Ceramics International

Volume 44, Issue 7, May 2018, Pages 7709-7715

https://doi.org/10.1016/j.ceramint.2018.01.197 Get rights and content

Abstract

Pb(Nd_xZr_0.52Ti_0.48)O₃ (PNZT) (x = 0%, 1%, 2%, 3%, 4%, 5%) thin films were prepared by sol-gel process to investigate the effects of neodymium substitution on crystalline orientation, microstructure and electric properties of lead zirconate titanate (PZT) films. X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis showed that PNZT films with Nd doping concentration below 3% exhibited dense perovskite structure with (100) preferred orientation. The average grain size of PNZT films decreased as the Nd substitution increased. The maximum dielectric constant, remnant polarization and minimum coercive field were obtained in 2% Nd-doped PZT films. Fatigue resistance was also improved significantly with 2% Nd dopant.

Introduction

PZT thin films have been extensively studied due to their excellent dielectric, ferroelectric and piezoelectric properties, which make it possible for various applications such as energy harvesters, microactuators and ferroelectrics capacitors [1], [2], [3]. A variety of fabrication methods of PZT thin films include sputtering, pulsed laser ablation deposition (PLAD), chemical solution deposition (CSD) and sol-gel process [4], [5], [6], [7]. Among them, the sol-gel process has been widely used because of its ease of doping modification, facility of stoichiometry control and low cost of fabrication.

The properties of PZT films depend strongly on many parameters, including stoichiometric composition, doping and microstructure evolution [8], [9], [10]. Guo et al. reported that (100)-oriented PZT films in the vicinity of morphotropic phase boundary (MPB) composition received higher piezoelectric constant and enhanced piezoelectric response [8], [11]. After repeated polarization switching, PZT films suffer significant ferroelectric fatigue because of migration of space charge. In order to fabricate (100)-oriented PZT films and relieve fatigue problem, many efforts have been focused on depositing PZT films onto buffer layer, such as PbO, MgO and PbTiO₃ buffer layers [6], [12], [13]. However, introducing buffer layer will increase the cost and complexity of process.

Doping is often used to enhance the properties of PZT thin films. So far, a great quantity of work have been done to evaluate crystalline orientation and electric properties of PZT films by doping Gd, Mn, Nb, La, etc. [6], [14], [15], [16]. In particular, the neodymium (Nd) additive is considering as positive doping to improve dielectric, ferroelectric and piezoelectric properties of PZT films. Majumder found a diffuse phase transition and the effect of Nd doping on dielectric and ferroelectric properties of PZT films [17]. Mohiddon investigated the grain size, maximum dielectric constant and dielectric losses of PZT ceramics with Nd doping, and all PZT ceramics exhibited (110) preferred orientation [18]. Therefore, preparing (100)-oriented PNZT thin films on Pt(111)/Ti/SiO₂/Si(100) substrates still remains a challenge. In addition, there are few studies to discuss the effect of Nd doping concentration on crystalline orientation, dielectric, ferroelectric properties and fatigue resistance of sol-gel-derived PZT thin films.

In this paper, Nd-doped PZT films with different doping concentration(0%, 1%, 2%, 3%, 4% and 5%) were fabricated on Pt(111)/Ti/SiO₂/Si(100) substrates by sol-gel methods. Without introducing buffer layers, (100)-oriented PNZT thin films with excellent fatigue resistance were obtained by using conventional furnace heat process and appropriate doping concentration. Simultaneously, the effects of neodymium substitution on crystalline orientation, microstructure, dielectric, ferroelectric and fatigue resistance of PZT thin films have been investigated.

Section snippets

Sample design and preparation

The PNZT precursor solutions were prepared with nominal compositions of Pb(Nd_xZr_0.52Ti_0.48)O₃ (x = 0%, 1%, 2%, 3%, 4%, 5%). The selected raw materials for preparing the precursors were lead acetate trihydrate (Pb(CH₃COO)₂·3H₂O), zirconium nitrate (Zr(NO₃)₄·5H₂O), tetrabutyl titanate (C₁₆H₃₆O₄Ti) and neodymium nitrate hexahydrate (Nd(NO₃)₃·6H₂O). Acetylacetone (C₅H₈O₂) was used as the chelating agent and 2-methoxyethanol (C₃H₈O₂) as the solvent. The lead acetate trihydrate, zirconium nitrate,

The crystalline orientation of PNZT thin films

Fig. 1 shows the XRD patterns of undoped and neodymium substituted PZT thin films with different Nd doping concentration. As can be seen, all films exhibit complete perovskite structure and no pyrochlore phase is observed. When the Nd doping concentration is lower than 3%, the PNZT films exhibit combined orientations of the (100), (110) and (111) directions, in which the (100) orientation dominates growth direction and (100) orientation diffraction peak gradually enhances with increased Nd

Conclusions

The PNZT thin films with different Nd doping concentration (0%, 1%, 2%, 3%, 4% and 5%) were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by sol-gel process. Simultaneously, the effects of neodymium substitution on crystalline orientation, microstructure and electric properties of PZT thin films were investigated. As the Nd doping concentration was less than 3%, the PNZT films exhibited (100) preferred orientation with dense and columnar perovskite structure. The maximum dielectric constant of

Acknowledgements

This paper was supported by National Natural Science Foundation of China (No. 51775088) and Science Technology Project of Guangdong Province, China (No. 2015B090920001).

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Effect of neodymium substitution on crystalline orientation, microstructure and electric properties of sol-gel derived PZT thin films

Abstract

Introduction

Section snippets

Sample design and preparation

The crystalline orientation of PNZT thin films

Conclusions

Acknowledgements

Phys. Lett. A

Appl. Surf. Sci.

J. Cryst. Growth

Acta Mater.

Phys. Rev. B: Condens. Matter

Ceram. Int.

Mater. Sci. Eng. B

Micro-fabricated flexible PZT cantilever using d33 mode for energy harvesting

Micro Nano Syst. Lett.

Multi-photon vertical cross-sectional imaging with a dynamically-balanced thin-film PZT z-axis microactuator

J. Microelectromech. Syst.

Compositional dependence of the Young's modulus and piezoelectric coefficient of (110)-oriented pulsed laser deposited PZT thin films