X-ray and magnetization studies on Li-Cu mixed ferrites

Abstract

Lithium ferrite possesses several attractive features that make it suitable for use in memory cores, microwave devices and cathode materials in lithium batteries [1]. Because of these features, substituted lithium ferrites have become important materials. To prepare the suitable substituted lithium ferrite it is necessary to know its structural, magnetic and electrical properties. X-ray, neutron diffraction and magnetization studies were carried out by many workers [2-4]. The effects of long-range ordering in substituted ferrites and its magnetic structure were also studied [5, 6]. The spinel system containing copper in lithium has been studied by quite few workers [7, 8]. We have therefore undertaken to investigate the Li-Cu system by X-ray and magnetization measurements in order to understand cation distribution and long-range ordering. (Li0.5 Fe0.5)~_xCu~ Fe204 ferrites were prepared by a standard ceramic method. Oxides of high purity of F%O3, CuO and the carbonate of lithium were mixed stoichiometrically and pre-sintered at 700°C for 4h, then crushed into powders and again fired at 950°C for 20 h and were furnace-cooled at a rate of 40 ° C h i. The fine powders were obtained by sieveing (38 #m) and pellets were prepared by pressing the compact powder. The X-ray diffractograms of the samples using Fe-K~ radiation were obtained. The magnetization of the sample was measured on a high-field loop tracer HS 869 (ECIL make). The method employed for measuring Curie temperatures was as discussed elsewhere [9]. Table I gives the lattice parameters for mixed Li-Cu ferrites of various compositions. In the case of lithium ferrite the value obtained is in good agreement with that reported by Gorter [10] and for CuF%O4 the value obtained is in good agreement with that reported by Patil [11]. The value of c/a varies from 1.01 to 1.06 for CuF%O4, due to the number of copper ions distributed on A and B sites in the crystal (Fig. 1). In the Li-Cu ferrite the compositions with x = 0, 0.2, 0.4 show cubic structure, whereas the compositions with x = 0.6, 0.8 and 1 show tetragonal structure.