A new variety of LiMnO2: high-pressure synthesis and magnetic properties of tetragonal and cubic phases of LixMn1-xO (x similar to 0.5)

Tetragonal and cubic phases of LixMn1-xO with x similar to 0.5 were success fully synthesized by a high-pressure technique in the pressure and temperat ure ranges of 4-6 Gpa and 900-1200 degreesC. respectively. The novel tetrag onal phase was obtained using an orthorhombic LiyMn1-yO powder with y < 0.5 as a starting material, whereas the cubic phase was obtained using y > 0.5 powders. The crystal structure of the tetragonal Li0.39Mn1.07O2 was isomor phous to that of LiInO2 of space group I4(1)/amd with the lattice parameter a = 0.41919 nm, c = 0.82469 nm and z = 4. On the other hand, the cubic Li1 .1Mn0.9O2 was found to be of a NaCl-type structure with both Li and Mn ions randomly occupy the cation site. As temperature decreased from 400 K, the tetragonal phase exhibited magnetic phase transitions successively from par amagnetic to antiferromagnetic at T-N = 280 K and from antiferromagnetic to spin-glass at T-F = 42 K, while the cubic phase showed only a magnetic pha se transition from paramagnetic to spin-glass at T-F = 45 K. (C) 2001 Elsev ier Science B.V. All rights reserved.