EPR Study of Water Induced Decomposition of the SrCuO$\text{}_{2}$ and Sr$\text{}_{2}$CuO$\text{}_{3}$ Ceramics Surface. The Role of Carbon Dioxide

Processes of SrCuO$\text{}_{2}$ and Sr$\text{}_{2}$CuO$\text{}_{3}$ ceramics decomposition induced by contact with water and carbon dioxide were studied by EPR. The dominant signals in the spectra were found to originate from Sr$\text{}_{2}$Cu(OH)$\text{}_{6}$ (for Sr$\text{}_{2}$CuO$\text{}_{3}$) and SrCu(OH)$\text{}_{4}$·H$\text{}_{2}$O (for SrCuO$\text{}_{2}$) compounds. The thermally induced conversion of SrCu(OH)$\text{}_{4}$·H$\text{}_{2}$O into Sr$\text{}_{2}$Cu(OH)$\text{}_{6}$ was analysed, and its product CuO was found to exist in the nanocrystalline form. The presence of CO$\text{}_{2}$, reacting with Sr(OH)$\text{}_{2}$, was shown to modify the decomposition process leading to the appearance of SrCu(OH)$\text{}_{4}$·H$\text{}_{2}$O, some hydroxycarbonates and Cu(OH)$\text{}_{2}$ on the surface of ceramics studied. At temperatures higher than 300ºC CuO reacts back with Sr(OH)$\text{}_{2}$. For the samples being in contact with atmospheric moisture this compound, deposited on a surface of SrCuO$\text{}_{2}$, decomposes to Sr$\text{}_{2}$Cu(OH)$\text{}_{6}$. The presence of the antiferromagnetic compounds Cu(OH)$\text{}_{2}$, CuO, and Cu$\text{}_{2}$[(OH)$\text{}_{2}$CO$\text{}_{3}$] in the samples can influence the results of magnetic measurements of the studied ceramics.