{'fraction_non_alphanumeric': 0.024759284731774415, 'fraction_numerical': 0.009628610729023384, 'mean_word_length': 5.736111111111111, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Thermally Induced Changes in the Structure, Composition, and Chemical Properties of LiMn2O4 ±x Spinel Prepared by Sol–Gel Method

Sol–gel method followed by calcination at temperatures of 300–900 °C was used to obtain a series of LiMn2O4 samples with varying amounts of chemical and structural defects while preserving a constant Li:Mn atomic ratio. The physicochemical and structural properties of the samples were characterized by X-ray diffraction (XRD), thermal gravimetry analysis–mass spectrometry (TGA–MS), differential scanning calorimetry (DSC), and Raman spectroscopy techniques. These results were correlated with separately performed high-frequency EMR measurements on the same samples. The oxidation number of Mn ions changes as compared with the stoichiometric spinel composition LiMn2O4. These changes, induced by the removal or incorporation of oxygen, were analyzed and correlated with the appearance or disappearance of the cubic to orthorhombic phase transition at around room temperature. The phase transition occurs only if the concentration of vacancies (cationic or anionic) is below the limit necessary to form sufficient majority of perfect MnO6 octahedra of the high symmetry, Oh7. Disturbance of this high local symmetry, being a condition for Jahn–Teller distortion, seems to also be the decisive factor in suppressing the phase transition that is regarded to be responsible for electrical capacity fading during cell cycling.