Journal of Magnetism and Magnetic Materials 248 (2002) 200–215 Ti 4+ and Ge 4+ ionic substitution in Cu-ferrite, electrical conductivity and thermoelectric power S.A. Mazen*, H.M. Zaki Department of Physics, Faculty of Science, Zagazig University, Zagazig, A.R., Egypt Received 15 August 2001; received in revised form 8 March 2002 Abstract Both the DC conductivity and the thermoelectric power of Cu 1+x Ge x Fe 22x O 4 and Cu 1+x Ti x Fe 22x O 4 ferrites, for 0pxp0:4; were measured in a wide range of temperature from RT up to 773 K. The measurements showed that the substitution of both tetravalent ions (Ge 4+ and Ti 4+ ) tend to convert Cu-ferrite from n- to p-type semiconductor. The results were analyzed on the basis of the small polaron model. The cation distribution for each system was proposed. The activation energy DE; Fermi energy E F ; the density of charge carriers n or p and the carriers mobility m were determined for both systems. In addition, an energy band schemes of Cu–Ge and Cu–Ti ferrites were schematically represented. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Ferrites; Transport properties; Conductivity; Thermoelectric power 1. Introduction For its uniqueness, Cu-ferrite has attracted the attention of investigators. It shows structural sensitivity. In addition, the electrical and magnetic characteristics can be controlled and innovated by many factors. Among these are the preparation conditions, cation distribution and ions substitu- tion [1–3]. In an analogous study, some physical properties were investigated against Ti ions sub- stitution in Cu-ferrite with two chemical formulae [4]. It has been recognized that a combination between two ions, one with low and another with high charge ions might produce modification to the ferrite characteristics [5]. A combination as such can be fulfilled by introducing tetravalent ion in the Cu-ferrite. Recently, X-ray analysis and IR absorption have been studied [1]. In this study Ge and Ti ions were alternatively substituted in Cu-ferrite with chemical formulae Cu 1+x Ge x Fe 22x O 4 and Cu 1+x Ti x Fe 22x O 4 , for 0pxp0:4: Ge 4+ and Ti 4+ were selected as examples for tetravalent ions with different electronic configuration. The study re- gards the transport properties such as conductiv- ity, thermoelectric power and mobility. The temperature and cationic parameter dependence were taken into consideration. 2. Experimental technique Two systems of ferrite, Cu 1+x Ge x Fe 22x O 4 and Cu 1+x Ti x Fe 22x O 4 with x ¼ 0; 0:1; 0:2; 0:3 and 0.4 were prepared using the standard ceramic *Corresponding author. Fax: +20-55-32-32-52. 0304-8853/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0304-8853(02)00281-0