А Mossbauer study of the state of iron atoms during the low-temperature synthesis of cristobalite in the $SiO_2-Fe_2O_3$ system

А Mossbauer study has been carried out of the process of low-temperature crystallization of cristobalite under hydrothermal conditions from а gel of the composition Si02 + 0.3 mass percent 57 Fе2 0з. It has been shown that in the original gel the paramagnetic Fe3+ ions are in the form of а diluted impurity in the diamagnetic matrix, with а spin-lattice relaxation oftheir magnetic moments being observed. At the beginning of the synthesis process the iron atoms are reduced to а divalent higl1-spin state with а sixfold oxygen coordination, and then, when cristobalite is formed, there occur the reverse oxidation and the formation of magnetically ordered Fe2 0 3 particles with sizes of 80 А< d < 300 А. No entry of iron atoms into tetrahedral positions of the structure has been observed.