Physica B 382 (2006) 271–278 Study of the ferroelectric properties of Ge–Sb–Te alloys A.A. Bahgat à , E.A. Mahmoud 1 , A.S. Abd Rabo 1 , Iman A. Mahdy 1 Department of Physics, Faculty of Science, Al-Azhar University, Nasr City 11884, Cairo, Egypt Received 22 December 2005; received in revised form 22 February 2006; accepted 25 February 2006 Abstract Some physical, electrical and ferroelectric properties of Ge 40 Sb x Te 60x alloys where x ¼ 1, 5 and 10 wt% as well as of Ge 50 Te 50 in the bulk state were studied. The X-ray diffraction measurements show that all the prepared samples are in crystalline state. Differential thermal analysis measurements show that the melting point decreases when Sb replaces Ge or Te. All samples having Sb show a solid–solid (structural) transformation and ferroelectric–paraelectric transition. These transition temperature increases as Sb content increases. The DC electrical resistivity measurements on the other hand indicated that all samples show metallic behavior. Measurements of the dielectric constant as a function of temperature at frequency 1 kHz for Ge 50 Te 50 sample give an indication that this material is a normal displacive ferroelectric showing first-order phase transition. Measurements of the polarization as a function of applied field for all samples at frequency of 60 Hz was found in good agreement with the Langevin function especially for Ge 50 Te 50 and Ge 40 Sb 5 Te 55 samples. The dielectric permittivity on the other hand shows for all samples a reversal nonlinear quadratic behavior as the applied electric field is increased. r 2006 Elsevier B.V. All rights reserved. PACS: 64.70.Kb; 71.20.Nr; 77.22.d; 78.30.Er Keywords: Ferroelectricity; GeTe; DC conductivity; Dielectric permittivity and polarization 1. Introduction Chalcogenide materials especially those containing Ge and Te are of importance in modern technology due to the following reasons: (1) large change in optical constants between crystalline and amorphous state and (2) rapid phase transition between amorphous and crystalline (two stable states) states [1]. This indicates that it can be used as an optical recording material (in optical memory devices such as CD or DVD). Also this material has high piezoelectricity, which make it applicable in many other applications. The existence of ferroelectricity in this alloy makes it useful as a base for ferroelectric memory, which is of a great importance in the field of modern computers industry. Vengalis and Kastal’ Skii [2] investigated the ferroelec- tricity of GeTe single crystal by the plasma reflection spectra, and found that the GeTe has a heterophase state. Chattopadhyay et al. [3] studied the structural phase transition of GeTe using neutron diffraction. They found that the material has a ferroelectric property with second- order phase transition and has the displacive-type phase transition. Rabe and Nopoulos [4] studied the structural properties of GeTe, they found that theoretical calculation and experimental measurements of convergence of lattice parameter, elastic constants and band structures of the rock salt and rhombohedra forms of GeTe are in good agreement. The possibility of light-induced phase transition in GeTe ferroelectrics was examined recently by Hase et al. [5], using amplified femto-second laser pulses, they noted that, the red shift of the soft mode induced by the second pulse excitation is caused by the electronic weakening of the crystal bonding due to excitation of the valance electrons. The crystallization kinetics of Ge 4 Sb 1 Te 5 films have been investigated using temperature dependence sheet resistance measurements in conjunction with structural investigations employing X-ray diffraction (XRD) and X-ray reflectometery by Wamwangi et al. [6]. They found ARTICLE IN PRESS www.elsevier.com/locate/physb 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.02.029 à Corresponding author. E-mail address: alaabahgat@hotmail.com (A.A. Bahgat). 1 Girls branch.