Quantitative analysis of gases by Raman spectroscopy is based on relative Raman scattering cross-sections (RRSCS) and the evolution of different spectral parameters (peak position, peak area, peak intensity, etc.). However, most of the calibration data were established at low pressure (low density) and without evaluating the effect of the composition. Using these data may lead to considerable errors, especially when applied to gas mixtures at high pressure as found in natural fluid inclusions. The aim of this study is to reevaluate the RRSCS of CO2 and to establish new calibration data based on the variation of CO2 Fermi diad splitting as a function of pressure (density) and composition over a pressure range of 5 to 600 bars at 22 and 32 °C. A high-pressure optical cell system (HPOC) and a heating-cooling stage were used for Raman in-situ analyses at controlled PTX conditions. Our experimental results show that the RRSCS of CO2 varies slightly with pressure but can be considered constant over the studied pressure range. It can be used to measure the proportion of CO2 in gas mixtures with an uncertainty of about ± 0.5 mol%. Different polynomial equations were provided to calculate pressure and density of CO2-N2 gas mixtures with an uncertainty of ± 20 bar or 0.01 g.cm −3. A comparison of PVTX properties of natural CO2-N2 fluid inclusions hosted in quartz from the Central Alps (Switzerland) obtained by Raman measurement and as derived from phase transition temperatures by microthermometry experiments shows comparable values. ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Detailed uncertainty calculations and the coefficients of regression polynomial equations 3, 4 and 5 (PDF)

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Lithiated transition metal oxides are active materials used as positive electrode in lithium ion cells thanks to their high capacity and air stability when. Amongst lithiated oxides, LiCoO2 is the most commonly and practically used due to its high‐specific energy and its excellent cycle life. This work focuses on phase transformation of LiCoO2 thin films during the annealing step and during the cycling life. The formation of unwanted products is highlighted by an innovative method: in situ Raman analysis. During the annealing used to transform the almost amorphous as‐deposited LiCoO2 into the rhombohedral structure useful for electrochemical cycling, the formation of Co3O4 has been observed. The second studied phase transformation is due to the electrochemical cycling and highlights the kinetics of the structure change. The study was done by comparing ex situ and operando results and highlights the main advantages of operando analysis: more data in a shorter time and the ability to assess the time dependence of phenomena.