High-pressure phase transition in LiMn 2 O 4 P. Piszora, W. Paszkowicz 2 , W. Nowicki, R. Minikayev 2 and C. Lathe 3 Adam Mickiewicz University, Grunwaldzka 6, 60-870 Poznan, Poland, 2 Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland 3 GeoForschungsZentrum Potsdam, Telegrafenberg A17, D-14473 Potsdam, Germany Lithium-manganese spinel oxide has been the subject of many previous investigations in different domains, however most studies have concentrated on the electrochemical character of the system, in view of its commercial application as a substitute for LiCoO 2 [1,2]. During the last 10 years several experimental studies on its high and low temperature phase transitions [3,4] and also theoretical calculations [5] have been carried out. Previous experimental high-pressure investigations of spinel structure oxides include studies of compressibility and phase transitions of many oxides e.g. ZnMn 2 O 4 [6], NiMn 2 O 4 [7], CuMn 2 O 4 [8], missing lithium manganese spinel. It is established that at ambient pressure the cubic-orthorhombic phase transition for pure LiMn 2 O 4 occurs at about 280 K. Lithium deficient Li 1-x Mn 2+x O 4 samples obtained at 800°C and quenched rapidly in the solid CO 2 exhibit two kind of tetragonal structures with c/a>1 and c/a<1 [9]. The effect of pressure on the structure of this material is as well of great interest. The main intention behind the present experiment was to study the effect of pressure on LiMn 2 O 4 by X-ray diffraction and to compare its structure transformation with the one described for low and high temperatures. The LiMn 2 O 4 sample has been obtained by solid state reaction of Li 2 CO 3 with the manganese oxide precursor, α-Mn 2 O 3 in air at 700°C and 800°C. The synchrotron X-ray powder diffraction data at ambient conditions confirm the cubic spinel structure, with the lattice constant resulting from Rietveld refinement, a=8.24483(4)Å [10]. The high-pressure powder diffraction experiment was performed using the energy dispersive X-ray diffraction method at a cubic anvil X-ray diffraction press, the MAX80 installed at the F2.1 synchrotron beamline at DESY/HASYLAB. The sample was mounted in a boron nitride cylinder inside a vertical cylindrical graphite heater located in the middle of a cube made of a boron-epoxy mixture. The X-ray detection system was based on a germanium solid-state detector of resolution 135eV at 6.3 keV. The characteristic feature of the experimental setup applied was the use of white synchrotron radiation combined with a diffraction angle fixed at θ = 4.5893°. Expecting for high-pressure condition the deformation of cubic structure analogous to that known from the temperature investigations we tried to index of high-pressure pattern according to well- defined tetragonal and orthorhombic structures. In the whole pressure region applied, 0< p <26 kbar, one may observe a mixture of cubic phase with space group Fd3m (a= 8.2456(20) Å at p = 0 kbar) and of tetragonal F4 1 /ddm phase (a= 8.176(16) Å, c=8.663(20) Å at p = 26 kbar). Nevertheless, the content of cubic phase declines and the tetragonal phase increases with pressure. Unit cell of the cubic LiMn 2 O 4 remains almost stable with pressure. The structure deformation at high-pressure is much higher then in low temperature case, where for orthorhombic structure (Fddd), at 250 K, c/a = 0.9938 [10]. The obtained value of c/a = 1.06 suits excellently with the results for the Li 0.9 Mn 2.1 O 4 sample, quenched from 800°C [9]. Acknowledgements The synchrotron measurements at HASYLAB were supported by the IHP-Contract HPRI-CT- 1999-00040/2001-00140 of the European Commission and by the Committee for Scientific Research (Poland) by the grant 4 T09A 164 23 (2002-2004).