High T c ferroelectricity in Ba-doped ZnO nanoparticles Gunjan Srinet, Ravindra Kumar n , Vivek Sajal Department of Physics and Materials Science and Engineering, Jaypee Institute of InformationTechnology, Noida 201307, Uttar Pradesh, India article info Article history: Received 6 February 2014 Accepted 9 April 2014 Available online 18 April 2014 Keywords: Semiconductors Ferroelectrics Luminescence abstract Effects of Ba doping on structural, optical and ferroelectric properties of ZnO nanoparticles prepared by a low cost thermal decomposition method are presented. The substitution of Ba on Zn sites of the wurtzite structure of ZnO was observed by X-ray diffraction. Some structural transformation in the morphology of nanostructure with Ba doping was observed. Redshift in band gap is observed in the UV–visible spectra after Ba doping, supported by photoluminescence spectra and showing enhanced defect states with Ba doping. In dielectric studies, high value of dielectric constant and transition temperature at ( 330 1C) were observed. High value of remnant polarization (1.01 mC cm 2 ) and low value of coercive field (2.02 kV cm 1 ) were also observed in ferroelectric studies which can be useful for potential applications. & 2014 Elsevier B.V. All rights reserved. 1. Introduction ZnO is a wide band gap (3.37 eV) semiconductor having unique features such as large exciton binding energy (60 meV) and large ferromagnetic and piezoelectric coefficients with a predicted curie temperature above room temperature when doped with the transition metal [1–3]. It is one of the potential semiconductors for developing blue and ultra violet (UV) photonic and spin photonic devices such as light emitting diodes (LED), laser diodes, solar blind UV photodetector, fast UV sensors and transparent electronic devices [4]. More interestingly, recent developments showed that doped ZnO is diluted magnetic semiconductor (DMS) which attracted considerable interest due to its potential applica- tion in spintronics [5]. There are several reports available in the literature on optical and magnetic properties of transition and non-transition metal doped ZnO [2,6], but still it is a good candidate for improving ferroelectric (FE) properties, which are of considerable importance in low dimensional ferroelectrics because of the demand for non-volatile FE memory device miniaturization [7,8]. Generally, pervoskites are used for FE memory devices which are structurally complicated and difficult to synthesize [9,10]. There are only few ZnO based FE materials reported in the literature which are highly controversial. Yadav et al. [11] observed dielectric anomaly at 430–460 K and claimed the anomaly not to be ferroelectric, Gupta et al. [12] reported ferroelectric transition around 343 K in K doped ZnO nanorods, Yang et al. [13] observed and explained the multiferrioc behavior of Cr doped ZnO. Recently, Gupta et al. [14] observed low ferro- electric phase transition at 69 1C. Under this scenario, ferroelectric and dielectric properties of doped ZnO systems are highly interesting for scientific research. In this paper, we used a thermal decomposition method for the preparation of Ba doped ZnO nanoparticles and studied the structural, vibrational, optical, dielectric and ferroelectric proper- ties. Further, till now, there are no reports available on ferroelectric studies of Ba doped ZnO nanoparticles. 2. Experimental details Ba doped ZnO nanoparticles were synthesized by the thermal decomposition method by using chemicals of analytical grade. Initially, 0.16 mol C 2 H 5 O 4  2H 2 O (oxalic acid) was dissolved in 100 ml of deionised (DI) water with vigorous stirring. Then, 0.02 mol diethanolamine (DEA) is added to get homogenous DEA/C 2 H 5 O 4  2H 2 O solution (A). Now, 0.02 mol zinc nitrate was dissolved in 100 ml of DI water in which appropriate amount of barium nitrate (5%) was added to get the solution B. Finally, B was added dropwise in the aqueous solution A. White precipitates were formed and the suspension was continuously stirred at room temperature and kept for 12 h to settle down. Then, precipitates were filtered, washed with DI water and ethanol water several times, dried at room temperature and calcined at 500 o C for 2 h. The crystalline structure and the phase purity of samples were confirmed by X-ray diffraction (XRD) measurements (Shimadzu XRD-6000 with CuKα (λ ¼ 1.5406 Å) radiation). Absorption spectra were carried out by a Perkin ElmerLambda-35 UV–visible spectro- meter in the wavelength range 300–800 nm. Photoluminescence (PL) spectra were acquired using xenon flash lamp laser as Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/matlet Materials Letters http://dx.doi.org/10.1016/j.matlet.2014.04.054 0167-577X/& 2014 Elsevier B.V. All rights reserved. n Corresponding author. E-mail address: ravindrakbhatt@gmail.com (R. Kumar). Materials Letters 126 (2014) 274–277