Apatite-type lanthanum silicates (ATLS), especially doped ones, have recently attracted a considerable attention due to their high ionic conductivity at intermediate temperatures but their usual synthesis requires too long firing cycles at ~1500°C. To promote ATLS application, the development of low-temperature preparation methods is necessary. Earlier, mechanochemical treatment has been successfully used for a low-temperature synthesis of undoped ATLS.

In this work, the results on the formation of Al-doped ATLS in the course of mechanochemical activation (MA) in a high-power planetary ball mill at room temperature are presented. Phase and structure evolution during 5-35 min MA of a stoichiometric mixture containing La₂O₃, Al(OH)₃ and amorphous SiO₂ were investigated using XRD, IR, NMR and TEM methods. At the first MA stage, a strong structure disorder of the initial La₂O₃ and SiO₂ occurs with a formation of an amorphous aluminosilicate phase as a result of interaction of SiO₂ and Al(OH)₃ and, at the same time, an apatite phase starts to form. At increasing MA time, further interaction of highly disordered La₂O₃ and amorphous aluminum silicate which cover La₂O₃ particles suggests the formation of highly crystalline ATLS with a particle size of 10-60 nm. Subsequent MA of formed ATLS leads to distortion of ATLS anion sublattice and to destruction of some share of ATLS resulted in the formation of LaAlO₃. The latter fact shows a restriction of Al-substitution on Si-sites into ATLS.

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