Direct synthesis and characterization of mixed-valent Li-0.5-delta CoPO4, a Li-deficient derivative of the Cmcm polymorph of LiCoPO4
| Autor: | Ludwig, Jennifer, Alarcon-Suesca, Carlos, Gepraegs, Stephan, Nordlund, Dennis, Doeff, Marca M., Puente Orenchef, Ines, Nilges, Tom |
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| Přispěvatelé: | Tech Univ Munich, Dept Chem Synth & Characterizat Innovat Mat, Lichtenbergstr 4, D-85747 Garching, Germany, Bavarian Acad Sci & Humanities, Walther Meissner Inst, Walther Meissner Str 8, D-85747 Garching, Germany, SLAC National Accelerator Laboratory (SLAC), Stanford University, Lawrence Berkeley National Laboratory [Berkeley] (LBNL), Inst Ciencia Mat Aragon, Pedro Cerbuna 12, Zaragoza 50009, Spain, Institut Laue-Langevin (ILL), ILL |
| Jazyk: | angličtina |
| Rok vydání: | 2017 |
| Předmět: | |
| Zdroj: | RSC Advances RSC Advances, Royal Society of Chemistry, 2017, 7 (45), pp.28069-28081. ⟨10.1039/c7ra04043a⟩ |
| ISSN: | 2046-2069 |
| DOI: | 10.1039/c7ra04043a⟩ |
| Popis: | International audience; While the majority of research activities on LiCoPO4 is focussed on the thermodynamically stable olivine-type Pnma polymorph, the metastable Pna2(1) and Cmcm modifications have recently attracted considerable attention due to their interesting material properties. In this study, we present the first Li-deficient structural derivative of the Cmcm modification with the nominal composition Li-0.5-delta CoPO4. As opposed to the substoichiometric olivine (Pnma) phases LixCoPO4 (x = 0; 2/3), which are exclusively accessible by electrochemical or chemical Li extraction techniques, this is also the first time that a direct soft-chemical synthesis route towards a LixCoPO4-type material is accomplished. X-ray and neutron diffraction studies indicate that Cmcm-type Li-0.5-delta CoPO4 shows vacancies on both the Li and Co sites, whereas X-ray absorption spectra demonstrate that the structure features heterovalent Co ions (+2/+3) to compensate for the Li deficit. Magnetic measurements reveal a long-range antiferromagnetic order below 10.5 K. A thorough investigation of the thermal stability using thermogravimetric analysis, differential scanning calorimetry, and temperature-dependent in situ X-ray powder diffraction demonstrates that Li-0.5-delta CoPO4 is metastable and exhibits a complex, multi-step thermal decomposition mechanism. In the first step at 394 degrees C, it decomposes to alpha-Co2P2O7 (P2(1)/c) and LiCoPO4 (Cmcm) upon O-2 release. The LiCoPO4 (Cmcm) intermediate is then irreversibly transformed to olivine-type LiCoPO4 (Pnma) at 686 degrees C. The material properties of Li-0.5-delta CoPO4 are further compared to the fully lithiated, isostructural LiCoPO4 (Cmcm) phase, for which an improved structure solution as well as Co L-2,L-3-edge X-ray absorption spectra are reported for the first time |
| Databáze: | OpenAIRE |
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