(a) Schematic illustration of the crystal structure of LMO and (b) its oxygen sub-lattice along the  direction. LMO has a cubic spinel structure with a space group of , in which Li+ ions occupy both tetrahedral 8a and octahedral 16d sites, while Mn ions sit the octahedral 16d site. The oxygen positional parameter (u) at 300 K is about 0.388 for the x = 0 sample. The deviation from the ideal position u = 0.375 leads to the distortion of the oxygen sub-lattice.
(a) Piston cylindrical cell for high-pressure muon-spin rotation and relaxation measurements and (b) pressed Li[Li x Mn2 −x ]O4 disks.
wTF μSR spectra for the Li[Li x Mn2− x ]O4 sample with x = 0.1 at temperatures of 10 and 70 K at ambient pressure, P = 0.1 MPa. The applied magnetic field H wTF was 50 Oe. The muon asymmetry A wTF consists of the asymmetry from both sample and body of the high-pressure cell.
Temperature dependence of the normalized weak-transverse field asymmetry (N ATF) for the Li[Li x Mn2 −x ]O4 samples with (a) x = 0, (b) x = 0.1, and (c) x = 0.2 at pressures (P) of 0.1 MPa, 1.2 GPa, and 2.1 GPa. The value of N ATF was obtained by fitting the wTF-μSR spectra with Eq. (1) . was defined as temperature at which N ATF = 0.5. P dependence of is shown in the inset.
x dependences of (a) magnetic transition temperature ( ) at pressures (P) of 0.1 MPa and 2.1 GPa, (b) slope of with P (d /dP), and (c) cubic lattice parameter (a c) at P = 0.1 MPa and 300 K in Li[Li x Mn2 −x ]O4. The oxygen positional parameter (u) is also shown in (c).
Cyclic voltammogram of the Li/LMO cell with (a) x = 0, (b) x = 0.05, (c) x = 0.1, and (d) x = 0.2. Cyclic voltammetry was measured at scan rate of 0.1 mV·s − 1 in the voltage range between 3.0 and 4.5 V. The LMO-electrode mix is fixed to ∼22 mg for all the LMO cells in order to compare the values of the peak current at anodic direction (I pa) and cathodic direction (I pc). The x dependence of I pa and I pc is shown in (e).
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