| TEMPERATURE RANGE (ºC) | THERMAL PHENOMENA | PHASE TRANSFORMATION |
|---|---|---|
| 30–117 | Desorption of molecules, such as water, from the surface of α-MnO2 and Mn3O4 particles. | – |
| 117–454 | Reduction of α-MnO2 (204 ºC) and oxidation of Mn3O4 (355 ºC). Structural water removal. Hydroxyl desorption. | α-MnO2 → Mn3O4 Mn3O4 → Mn5O8 |
| 454–524 | Reduction of Mn5O8. | Mn5O8 → Mn2O3 Mn5O8 → Mn3O4 |
| 534–715 | Oxidation of Mn2O3 (657 ºC). O2 release. | Mn2O3 → Mn3O4 |
| 715–1200 | Ionic movement in the Mn3O4 network. Reduction of Mn3O4. Oxidation of Mn2O3 (1052 ºC). Transformation of the tetragonal Mn3O4 phase to cubic Mn3O4 (1175 ºC). O2 release. |
Mn3O4 ↔ Mn2O3 Tetragonal Mn3O4 → Cubic Mn3O4 |
| SAMPLE | ATOMIC PERCENTAGE (at%) | |
|---|---|---|
| Mn | Na | |
| MnO | 98.39 | 1.61 |
| MnO 160 ºC | 98.56 | 1.44 |
| MnO 480 ºC | 98.64 | 1.36 |
| MnO 715 ºC | 98.48 | 1.52 |
| MnO 870 ºC | 98.30 | 1.70 |
| MnO 920 ºC | 98.36 | 1.64 |
| MnO 1150 ºC | 98.76 | 1.24 |
| Mean Value | 98.50 | 1.50 |
| SAMPLE | AVERAGE CRYSTALLITE SIZES (nm) | ||||
|---|---|---|---|---|---|
| α-MnO2 | Mn3O4 | Mn5O8 | Na2Mn5O10 | Na4Mn9O18 | |
| MnO | 20.9 | 80.5 | – | – | – |
| MnO 160 ºC | 19.6 | 67.2 | – | – | – |
| MnO 480 ºC | – | 28.9 | 32.1 | – | – |
| MnO 715 ºC | – | 77.5 | – | 26.2 | – |
| MnO 870 ºC | – | 99.1 | – | – | 48.6 |
| MnO 920 ºC | – | 43.5 | – | – | 57.2 |
| MnO 1150 ºC | – | 46.5 | – | – | – |
| SAMPLE (REPLICA) | AVERAGE CRYSTALLITE SIZES (nm) | ||||
| α-MnO2 | Mn3O4 | Mn5O8 | Na2Mn5O10 | Na4Mn9O18 | |
| MnO | 21.3 | 72.5 | – | – | – |
| MnO 160 ºC | 20.5 | 70.7 | – | – | – |
| MnO 480 ºC | – | 31.9 | 33.3 | – | – |
| MnO 715 ºC | – | 72.5 | – | 30.2 | – |
| MnO 870 ºC | – | 84.2 | – | – | 48.2 |
| MnO 920 ºC | – | 44.6 | – | – | 53.4 |
| MnO 1150 ºC | – | 47.8 | – | – | – |
| SAMPLE | PHASE PERCENTAGE AND LATTICE PARAMETERS | RWP (%) | REXP (%) | χ2 | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| MnO | Tetragonal Mn3O4 (∼ 100 wt%)* | 3.121 | 1.766 | 1.330 | ||||||
| a,b (Å) | c (Å) | V (Å3) | ||||||||
| 5.7698 | 9.4521 | 314.67 | ||||||||
| MnO 160 ºC | Tetragonal Mn3O4 (∼ 100 wt%)* | 3.516 | 2.587 | 1.833 | ||||||
| a,b (Å) | c (Å) | V (Å3) | ||||||||
| 5.77033 | 9.4654 | 315.17 | ||||||||
| MnO 480 ºC | Tetragonal Mn3O4 (5.53 wt%) | Monoclinic Mn5O8 (94.47 wt%) | 10.053 | 4.274 | 5.533 | |||||
| a,b (Å) | c (Å) | V (Å3) | a (Å) | b (Å) | c (Å) | V (Å3) | ||||
| 5.7602 | 9.4885 | 314.83 | 10.4530 | 5.7560 | 4.8734 | 276.13 | ||||
| MnO 715 ºC | Tetragonal Mn3O4 (98.86 wt%) | Monoclinic Na2Mn5O10 (1.14 wt%) | 4.388 | 2.601 | 2.827 | |||||
| a,b (Å) | c (Å) | V (Å3) | a (Å) | b (Å) | c (Å) | V (Å3) | ||||
| 5.7626 | 9.4675 | 314.40 | 8.9605 | 11.0579 | 2.8053 | 277.96 | ||||
| MnO 870 ºC | Tetragonal Mn3O4 (90.22 wt%) | Orthorhombic Na4Mn9O18 (9.78 wt%) | 3.723 | 2.563 | 2.110 | |||||
| a,b (Å) | c (Å) | V (Å3) | a (Å) | b (Å) | c (Å) | V (Å3) | ||||
| 5.7633 | 9.4684 | 314.50 | 9.0986 | 26.1584 | 2.8254 | 672.47 | ||||
| MnO 920 ºC | Tetragonal Mn3O4 (89.36 wt%) | Orthorhombic Na4Mn9O18 (10.64 wt%) | 3.865 | 2.558 | 2.283 | |||||
| a,b (Å) | c (Å) | V (Å3) | a (Å) | b (Å) | c (Å) | V (Å3) | ||||
| 5.7631 | 9.4677 | 314.45 | 9.1049 | 26.1970 | 2.8255 | 673.94 | ||||
| MnO 1150 ºC | Tetragonal Mn3O4 (100 wt%) | 3.249 | 2.674 | 1.476 | ||||||
| a,b (Å) | c (Å) | V (Å3) | ||||||||
| 5.7648 | 9.4693 | 314.70 | ||||||||
| SAMPLE | BAND GAP (eV) | ||||
|---|---|---|---|---|---|
| α-MnO2 | Mn3O4 | Mn5O8 | Na2Mn5O10 | Na4Mn9O18 | |
| MnO | 2.82 | 3.15 | – | – | – |
| MnO 160 ºC | 3.23 | 3.59 | – | – | – |
| MnO 480 ºC | – | 5.92 | 2.79 | – | – |
| MnO 715 ºC | – | 3.68 | – | 3.47 | – |
| MnO 870 ºC | – | 3.78 | – | – | 3.40 |
| MnO 920 ºC | – | 3.87 | – | – | 3.42 |
| MnO 1150 ºC | – | 7.42 | – | – | – |
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