Journal of Alloys and Compounds 509 (2011) 6447–6451 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Charge ordering analysis by electrical and dielectric measurements in Ca 2-x Pr x MnO 4 (x = 0–0.2) compounds M.T. Tlili a,∗ , N. Chihaoui a , M. Bejar a , E. Dhahri a , M.A. Valente b , E.K. Hlil c a Laboratoire de Physique Appliquée, Faculté des Sciences, Université de Sfax, 300 Sfax, Tunisia b I3N and Physics Department, University of Aveiro, 3810-193 Aveiro, Portugal c Institut Néel, CNRS, Université J. Fourier, BP 166, 38042 Grenoble, France article info Article history: Received 11 November 2010 Received in revised form 12 March 2011 Accepted 15 March 2011 Available online 22 March 2011 Keywords: Ruddlesden–Popper manganites Charge-ordering Dielectric permittivity Impedance Activation energy abstract Ca 2-x Pr x MnO 4 (0 ≤ x ≤ 0.2) polycrystalline ceramic powders were synthesized by sol–gel method. The X- ray diffraction (XRD) profiles were indexed with a tetragonal and orthorhombic structure for Ca 2 MnO 4 and Pr-doped compounds, respectively. Electrical properties were investigated by dc and ac electrical measurements. The dc measurements have revealed an insulating state for all compounds in 80–350 K temperature range. Both dc and ac measurements have highlighted a charge ordering (CO) transition at T CO = 233 and 245 K for x = 0.175 and 0.2, respectively. The CO state was found to be accompanied by a jump of the hopping activation energy and a rapid rise of both dielectric permittivity and imaginary part of ac electrical impedance. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The interest in materials with perovskite structure is explained by their potential technological applications arising from their various and interesting physical properties [1–3]. The Mn-based perovskite oxides have been a renewed subject of numerous investigations in recent years [4–7], because of their colossal magnetoresistance and giant volume magnetostriction near room temperature, required by the technology of various sensors and magnetomechanical devices. The calcium-doped rare earth manganites with the formula Ln 1-x Ca x MnO 3 , where Ln = La, Pr or Nd, show a variety of electronic and magnetic properties, which result in an asymmetry between the electron and hole-doped regions. For Mn 3+ concentrations, the two sublattices (Mn 3+ and Mn 4+ ) become ordered and the elec- trons become localized, leading to a charge-ordering state (CO) with an associated antiferromagnetic (AF) behavior [8]. The CO state is related to the weakening of double-exchange (DE) mechanism within ferromagnetic (FM) clusters, explained by the interruption of Mn 3+ –O–Mn 4+ bond [2]. The CO property is not only limited to manganites [9,10]; but also other materials exhibit this property as well, as observed in NdBaFe 2 O 5 [11] and La 1/3 Sr 2/3 Fe 1-x Cr x O 3 [12] compounds. Moreover, it has been discovered that the CO ∗ Corresponding author. Tel.: +216 97094554; fax: +216 74676609. E-mail address: medtahar59@yahoo.fr (M.T. Tlili). process is accompanied by an increase of the dielectric proper- ties [13,14] and is particularly reported that Pr 0.65 Ca 0.28 Sr 0.07 MnO 3 single crystal has high capacitive behavior just below T CO = 250 K (T CO : CO temperature) [15]. Polycrystalline La 1.5 Sr 0.5 NiO 4 [16], CaMn 7 O 12 [17,18] and thin films La 1-x Ca x MnO 3 [19,20] also have showed high values of the dielectric constant (ε r ) attributed to the important role of CO state. The Ruddlesden–Popper (RP) mangan- ites (Ln, A) n+1 Mn n O 3n+1 , which consist in a regular intergrowth of single rock-salt with multiple perovskite layers [21], display interesting magnetic, electrical and CO properties depending on material-doping. The Ca 2-x Ln x MnO 4 compounds (Ln = Pr, Sm, Gd, Ho), exhibiting a classical K 2 NiF 4 -type structure, are good examples of RP manganites and are a subject of diverse magnetic, electric, dielectric, and charge-ordering studies. For Ln = Pr, dielectric char- acterisation of Mn 3+ /Mn 4+ mixed oxides Ca 2-x Pr x MnO 4 (x = 0.25, 0.33 and 0.50) shows a CO transition at T CO depending on x-value [22]. In this paper, we report the Pr-doping effects on electrical and dielectric properties, in order to study the CO behavior in Ca 2-x Pr x MnO 4 compounds with a large doping range; x = 0.05, 0.125, 0.15, 0.175 and 0.2. The experimental study of dc resistiv- ity, ac impedance and dielectric permittivity, versus temperature and composition, is reported. 2. Experimental Polycrystalline Ca2-xPrxMnO4 compounds (x = 0–0.2) were prepared via sol–gel reaction by mixing high purity materials: Ca(NO3)24H2O (98%), MnO6 (99%) and 0925-8388/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2011.03.088