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=0 above room temperature, Ta, an orthorhombic phase becomes stable above Ta 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>PL∼10 GPa is applied to the sample, it transforms into an unexpected metastable distorted phase, which persists also when the external pressure is released.