An investigation of the synthesis of the layered perovskite RbCa2Nb3O10 using time-resolved in situ high-temperature powder X-ray diffraction

The Dion-Jacobson-type layered perovskite, RbCa2Nb3O10, has been prepared by two different synthetic routes at the moderate temperature of 800 degreesC. With a new molten salt approach, combining a 1:4:3 molar ratio of K2CO3:CaCO3:Nb2O5 with a large excess of RbCl leads to the rapid formation of RbCa2Nb3O10 at 800 degreesC. Although the product incorporates rubidium from the molten salt flux, K2CO3 is a necessary component of the reaction mixture. Surprisingly, the solid-state reaction of a 1.5:4:3 molar ratio of Rb2CO3:CaCO3:Nb2O5 at 800 degreesC also leads to the formation of RbCa2Nb3O10 in a relatively short time. Both of these reactions were studied by time-resolved in situ high-temperature X-ray powder diffraction. Energy-dispersive X-ray diffraction (EDXRD) data confirmed that the synthesis of RbCa2-Nb3O10 was accelerated by the molten salt flux; the material crystallizes as soon as the RbCl flux melts, and the reaction is shown to be complete within a few minutes of reaching 800 degreesC. The solid-state reaction proceeds more slowly but is still essentially complete in about 80 min. The in situ EDXRD data also revealed the presence of two or more intermediate phases produced in the solid-state synthesis, corroborated by laboratory quenching studies. Conventional high-temperature diffraction studies of RbCa2Nb3O10 established that no phase changes occur in this material up to 1000 degreesC.