Journal of Alloys and Compounds, 201 (1993) 103-104 103 JALCOM 725 Synthesis and structural characterization of two intercalated lithium and sodium copper iron selenides: LiCuFeSe2 and NaCuFeSe2 J. Llanos, C. Contreras-Ortega, J. Pfiez, M. Guzmfin and C. Mujica Departamento de Quimica, Facultad de Ciencias, Universidad Cat6lica del None, Casilla 1280, Antofagasta (Chile) (Received January 28, 1993; in final form March 10, 1993) Abstract The not new phases LiCuFeSe2 and NaCuFeSe2 were prepared from the corresponding carbonates and CuFeSe2. They crystallize as the isostructural sulphide phases LiCuFeS2 and NaCuFeS2 in the trigonal space group P3ml (No. 164) in a layered Li2FeSz structure type. The Se atoms form an h.c.p, array, the copper and iron atoms are statistically distributed in the tetrahedral sites whereas the alkali metals are placed in the octahedral sites in the van der Waals gap. 1. Introduction The use of transition metal sulphides as cathode materials in lithium high energy batteries has been intensively investigated [1--4]. Special effort has been invested in the identification and characterization of the lithium intercalated phases which are produced in the cathode during the discharge process. Among the transition metal sulphides, chalcopyrite shows very promising properties as cathode material [5, 6]. In order to gain a better understanding of the intercalation of lithium into copper iron chalcogenides, we have pre- pared LiCuFeSe2 and NaCuFeSe2 which represent the fully discharged cathodes of the system M/M+/CuFeS2 with M---Li or Na. The crystal structure of the new compounds was solved. 2. Experimental details Phases of composition LiCuFeSez and NaCuFeSe2 were prepared by heating stoichiometric amounts of Li2CO3 and Na2CO3 with CuFeSe2 at 1173 K. The latter compound was previously prepared by heating the elements at 973 K. The mixtures were contained in tightly sealed graphite crucibles and held at the reaction temperature over a period of 72 h. The X- ray diffraction patterns of the products showed that the materials were single phases. 3. Structure analysis Intensity data for LiCuFeSe2 were collected on a Syntex P1 diffractometer (Mo Ka; graphite monochrom- ator). Cell parameters were refined from 32 centred reflections. The intensities were measured in the to-20 scan mode and the absorption correction was done empirically by a ~0 scan. The powder X-ray diffraction pattern of NaCuFeSe2 was obtained with a Siemens D-5000 diffractometer fitted with a graphite mono- chromator and using the Cu Ka radiation (A = 1.540 57 /~) and silicon as internal standard. The evaluation of the powder diagrams showed that the compounds are isostructural. The lattice parameters of NaCuFeSe2 were refined with an iterative least-squares program. In Table 1 the crystallographic data and details of the structure analysis of LiCuFeSe2 and of NaCuFeSe2 are TABLE 1. Crystallographic data and details of the structure analysis for LiCuFeSe z and NaCuFeSe 2 LiCuFeSe~ NaCuFeSe2 Crystal system Trigonal Trigonal Space group P3m l P~3m l a (pm) 397.1(1) 400.8(3) c (pm) 664.6(4) 714.4(24) Z 1 1 Volume ( × 106 pm 3) 90.78(7) 99.4(5) /z (Mo Kct cm -1) 289.03 Diffractometer Syntex P1 Siemens D-5000 Radiation; monochromator Mo Ka; graphite Cu Ka; graphite Scan mode to-20 20 20max 45 80 Measured intensities 172 12 Unique reflection 95 Number of refined 11 parameters Final R; Rw 0.072; 0.061 0925-8388/93/$6.00 © 1993-Elsevier Sequoia. All rights reserved