Effect of Mg doping on the electrical properties of SnO 2 nanoparticles N. Mazumder, A. Bharati, S. Saha, D. Sen, K.K. Chattopadhyay * Thin Film and Nanoscience Laboratory, Department of Physics, Jadavpur University, Kolkata 700 032, India article info Article history: Received 9 August 2011 Received in revised form 19 November 2011 Accepted 26 December 2011 Available online 2 January 2012 Keywords: SnO 2 Mg doping Electrical properties XRD XPS abstract Solegel derived Mg doped tin oxide (Sn 1x Mg x O 2 ) nanocrystals were synthesized with x ranging between 0.5 and 7 at. %. Characteristic single phase tetragonal structure of pure and doped samples was obtained and doping saturation was inferred by X-ray diffraction analysis. Structural, morphological and phase informations were obtained by high resolution transmission electron microscope, field emission scanning electron microscope and X-ray photoelectron spectroscopy respectively whereas bonding information was obtained from Fourier transformed infrared spectroscopy. Measurement of different electrical parameters with frequency (200 Hze10 5 Hz) has been carried out at room temperature. Ultrahigh dielectric constant and metallic AC conductivity were observed for undoped tin oxide and the profiles reflected highly sensitive changes in the atomic and interfacial polarizability generated by doping concentrations. Relaxation spectra of tangent loss of any sample did not show any loss peak within the frequency range. Both the grain and grain boundary contributions are observed to increase as the doping concentration increased. Results of first principle calculation based on density functional theory indicated effective Fermi level (E F ) suppression due to Mg doping which is responsible for the experimentally observed conductivity variation. AC conductivity was found to depend strongly on the doping concentration and the defect chemistry of the compound. Mg doped SnO 2 may find applications as a low loss dielectric and high density energy storage material. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Even after few decades of intense research on the wide band gap oxide semiconductor nanomaterials, stannic oxide remains a very active material for research till date. Bulk SnO 2 has direct band gap of 3.6 eV and its nanocrystals (NC) possess ultrahigh dielectric constant in the low frequency region [1] and can be used as high density energy storage material [2], conductive film [3], high performance capacitor [4], dynamic RAM (volatile) [5], and as ferroelectric transparent thin film transistors [6]. The results of tailoring optical, electrical or magnetic properties of this non- stoichiometric 4d metal oxide depend on the nature of doping with specific impurity ions. The results of doping many d-block transition metals (TM) and rare earth (RE) elements in SnO 2 have been reported in literature recently [7e9]. In comparison, the electrical characteristics of the alkaline earth metal doped tin oxide have been studied to a lesser extent. So the purpose of controlling the dielectric and impedance profile of SnO 2 NCs with an element which do not contain ions with partially filled d bands promotes us to synthesize SnO 2 :Mg series through solegel route. Apart from lower processing temperature, this process has other advantages such as better homogeneity and dense monolith formation [10]. It was an unexplored topic till date how a material such as Mg which has spin polarized 2p states in the doped state [11] contributes to the rarest form of conductivity seen in this prototype non- stoichiometric transparent conductor. In fact it is the extremely sensitive profile of conductivity seen in this transparent conducting oxide (TCO) which makes it one of the best candidates among gas sensing materials [12]. The interplay between tin interstitial and oxygen vacancy along with the type of nanostructure are the phenomena responsible for the observed conductivity in SnO 2 . It is widely debated in recent literature whether SnO 2 offers excellent prospects for p-type doping by introduction of acceptors on the cationic site or not [13,14]. Calculation performed by Zhang et al. indicated that formation energy 0.48 eV for Mg doped SnO 2 , which implies that it can be easily synthesized in experiments [11]. We thought that it would be an interesting work to observe experi- mentally what resultant effect the s-block alkaline earth metal Mg doping would produce in the dielectric and conductivity profiles of SnO 2 . According to our knowledge, no experimental report is available in the literature on the Mg doped SnO 2 nanoparticles till date. So it is the first report on the structural and various electrical properties * Corresponding author. Tel.: þ91 33 24138917; fax: þ91 33 2114 6584. E-mail address: kalyan_chattopadhyay@yahoo.com (K.K. Chattopadhyay). Contents lists available at SciVerse ScienceDirect Current Applied Physics journal homepage: www.elsevier.com/locate/cap 1567-1739/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cap.2011.12.022 Current Applied Physics 12 (2012) 975e982