Stabilization of an orthorhombic phase in LiMn2O4 by means of high pressure

LiMn2O4 is considered a promising material for the Li ion battery technology. Moreover, this material has been largely investigated in the last few years because it presents a charge order transition around room temperature. In this paper, we studied the effect of applying an external hydrostatic pressure on the crystal structure of LiMn2O4 to have a better understanding of the phase diagram of this compound, stimulated also from the fact that many spinels undergo phase transitions under pressure. X-ray diffraction measurements were collected along three isotherms at 350, 385 and 415 K. The experimental data show that, while the symmetry of this sample is cubic for P=O above room temperature, T-a, an orthorhombic phase becomes stable above T. when an external pressure is applied on the sample. Moreover, it has been shown that, similarly to the behavior of other spinels, when a pressure P>P(L)similar to10 GPa is applied to the sample,it transforms into an unexpected metastable distorted phase, which persists also when the external pressure is released.