Abstract
In order to study a change in electrochemical, structural, and magnetic properties for lithium manganese oxide spinels Li[Li_{ x }Mn_{2} _{ −x }]O_{4} (LMO) with 0 ≤ x ≤ 1/3, muon-spin rotation and relaxation (μSR) spectra were recorded under pressure (P) up to 2.1 GPa. At ambient P, P = 0.1 MPa, the antiferromagnetic or spin-glass-like transition temperature (T _{m}) at P = 0.1 MPa monotonically decreases with increasing x. On the contrary, the slope of the T _{m} vs. P (dT _{m}/dP) rapidly increases from 0.9(1) K/GPa at x = 0 to 1.4 K/GPa at x = 0.1, then drops to 0.7(1) K/GPa at x = 0.15, and finally keeps constant (∼0.4 K/GPa) with further increasing x. Considering the structural change of LMO with x, the decrease in the distance between Mn ions (d _{Mn-Mn}) is likely to play an essential role for determining T _{m} under P. According to cyclic voltammetry on LMO, the peak current at both anodic and cathodic directions shows the maximum at x = 0.1, indicating the highest diffusivity of Li^{+} ions (D _{Li}) at x = 0.1.
We appreciate Professor T. Ohzuku, Dr. K. Ariyoshi, and Mr. H. Wakabayashi of Osaka City University for preparation of Li[Li_{ x }Mn_{2} _{ −x }]O_{4} and Mr. Y. Kondo of TCRDL for ICP-AES analyses. μSR was measured at the Swiss Muon Source, Paul Scherrer Institut (PSI). XRD experiment was performed at the SPring-8, Japan, with the approval of the Japan Synchrotron Radiation Research Institute (Proposal No. 2007A1917).We thank the staff of PSI and SPring-8 for help with the μSR and XRD measurements. This work was partially supported by Grant-in Aid for Scientific Research (B), Grant No. 19340107 provided by MEXT, Japan. D.A. acknowledges financial support from the Romanian UEFISCDI Project No. PN-II-ID-PCE-2011-3-0583 (85/2011).
I. INTRODUCTION
II. EXPERIMENTAL METHOD
III. RESULTS
IV. DISCUSSION
A. x dependence of d/dP
B. Correlation between d/dP and D_{Li}
V. CONCLUSION
Key Topics
- Muons
- 10.0
- Electrochemistry
- 7.0
- Electrodes
- 7.0
- X-ray diffraction
- 6.0
- Curie point
- 5.0
H01F1/00
Figures
(a) Schematic illustration of the crystal structure of LMO and (b) its oxygen sub-lattice along the [110] 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) Schematic illustration of the crystal structure of LMO and (b) its oxygen sub-lattice along the [110] 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 }Mn_{2} _{ −x }]O_{4} disks.
(a) Piston cylindrical cell for high-pressure muon-spin rotation and relaxation measurements and (b) pressed Li[Li_{ x }Mn_{2} _{ −x }]O_{4} disks.
wTF μSR spectra for the Li[Li_{ x }Mn_{2−} _{ x }]O_{4} 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.
wTF μSR spectra for the Li[Li_{ x }Mn_{2−} _{ x }]O_{4} 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 }Mn_{2} _{ −x }]O_{4} 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.
Temperature dependence of the normalized weak-transverse field asymmetry (N _{ATF}) for the Li[Li_{ x }Mn_{2} _{ −x }]O_{4} 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 }Mn_{2} _{ −x }]O_{4}. The oxygen positional parameter (u) is also shown in (c).
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 }Mn_{2} _{ −x }]O_{4}. 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).
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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