Electric and dielectric properties of pure and doped CaCu 3 Ti 4 O 12 perovskite materials G. Chiodelli a, * , V. Massarotti a,b , D. Capsoni a,b , M. Bini b , C.B. Azzoni c , M.C. Mozzati c , P. Lupotto d a CNR-IENI, Sezione di Pavia, viale Taramelli 16, 27100 Pavia, Italy b Dipartimento di Chimica Fisica ‘M. Rolla’ dell’Universita `, viale Taramelli 16, 27100 Pavia, Italy c INFM—Dipartimento di Fisica ‘A. Volta’ dell’Universita `, via Bassi 6, 27100 Pavia, Italy d Amel Electrochemistry, via G.B. de La Salle 4, 20132 Milano, Italy Received 15 July 2004; accepted 15 July 2004 by P. Wachter Available online 6 August 2004 Abstract AC impedance spectroscopy (IS) measurements were performed in the 15–700 K temperature range on pure and Ni, Fe and Co doped CaCu 3 Ti 4 O 12 (CCTO) materials. Capacitance values were also confirmed by direct current measurements at room temperature. Thermoelectric power measurements showed that the electrons are involved in the conduction process of the semiconducting bulk region. The IS results evidenced a dielectric behaviour in the grain boundary region, giving a permittivity of about 3400 for the pure sample, so CCTO can be considered an internal barrier layer capacitance (IBLC) material. The giant permittivity of CCTO can be strongly increased to values of w150 000 by Co doping on Ti site. The IBLC behaviour, together with the giant permittivity and the opportunity to combine capacitance and resistance values in an R//C circuit, evidence the applicability of this material as an integrated resonant element for the electronic industry. q 2004 Elsevier Ltd. All rights reserved. PACS: 77.22.Gm; 77.22Kd Keywords: A. Semiconductors; C. Grain boundaries; D. Dielectric response; E. Impedance spectroscopy 1. Introduction It is known that some compounds with perovskite structure display interesting dielectric properties [1]. In particular one of the members, CaCu 3 Ti 4 O 12 (CCTO), was recently studied to investigate the origin of the so called colossal permittivity [1–3], and results were published on single crystals [4], powders [5] and thin films [6,7]. This material is characterized by a conducting bulk and highly resistive grain boundary [8,9] and different theoretical models have been proposed to describe the dielectric response [10,11]. Moreover, EPR and Raman investigations were carried out to characterize CCTO and its derivatives by doping on Ca and/or Ti sites [12,13]. The aim of the present work is to study the electric (r) and dielectric (3 r ) properties of the pure and Co, Ni and Fe doped CCTO from 700 K down to 15 K by using the impedance spectroscopy (IS) and conductivity measurements. In particu- lar, AC IS is used to distinguish the intrinsic (bulk) and extrinsic (grain boundary) contributions, the latter resulting independent of sintering conditions. AC and direct current (DC) capacitance measurements are also used to measure the dielectric constant 3 r,exp pertinent to the grain boundary: its value rises up to 150 000 in Co doped samples. The use of a DC 0038-1098/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ssc.2004.07.058 Solid State Communications 132 (2004) 241–246 www.elsevier.com/locate/ssc * Corresponding author. Fax: C39-382-507910. E-mail address: gaetano.chiodelli@unipv.it (G. Chiodelli).