In situ synthesis, structural chemistry and vibrational spectroscopy of Zn-doped Ca5Mg4(VO4)6

The phase formation of the solid solution Ca5Mg4–xZnx(VO4)6 (0≤x≤4) was studied in situ using differential scanning calorimetry and high-temperature X-Ray powder diffraction (XRPD). XRPD analysis shows the appearance of unavoidable secondary pyrovanadate phases using conventional synthesis methods. The local structure of the solid solution was verified by vibrational spectroscopy. The analysis of the infrared and Raman spectroscopy data allows establishing the main features between vanadate garnets and their isostructural analogs among natural silicates

Reassessment of thermochemical energy storage in perovskite-like manganites at comparative studies of RP SrCa3Mn3O10-d vs. orthorhombic Sr0.25Ca0.75MnO3-d

The structural stability, thermal expansion, oxygen exchange thermodynamics, and thermochemical storage (TCS) capacity of perovskite-like Sr0.25Ca0.75MnO3-δ and Ruddlesden-Popper SrCa3Mn3O10-δ manganites are studied by the combined use of experimental techniques, thermodynamic modeling of the defect formation reactions, and energy calculations utilizing density functional theory (DFT). It is argued that conservative estimates of the storage capacity can be made by the use of the Dulong-Petit limit for high-temperature heat capacity and oxygen partial enthalpy independent of both temperature and oxygen content. The respectively recalculated literature data and the obtained results show that the thermodynamic limit for the TCS capacity (~800 kJ/kg) of Sr0.25Ca0.75MnO3-δ is one of the highest at thermal cycling within the oxygen partial pressure range of 10 −4–0.21 atm. At the same time, the storage capacity of SrCa3Mn3O10-δ achieves only about 600 kJ/kg. The TCS cycling tests demonstrate the stability of SrCa3Mn3O10-δ while a decline in the energy storage capacity is observed for Sr0.25Ca0.75MnO3-δ. According to the EDX analysis, this effect may reflect surface degradation of Sr0.25Ca0.75MnO3-δ. The energy storage capacities of SrCa3Mn3O10-δ and Sr0.25Ca0.75MnO3-δ decrease to 510 and 560 kJ/kg, respectively, because of the rather sluggish reduction kinetics. It is concluded that further improvement of manganites as energy storage materials can be achieved using new doping strategies.This work was carried out under support of the state programs № АААА-А19-119031890026-6 and № АААА-А19-119110190048-7. Part of the DFT calculations were performed on the URAN cluster at the Institute of Mathematics and Mechanics, UB RAS.Peer reviewe