Soft-Chemistry Approach To Synthesize Al 3+ , Ga 3+ , and Zr 4+ Stabilized Ion-ExchangeableLayered Perovskite Oxides

Protonated oxides, H2[Sr2Nb2MO9.5] (M = Al, Ga) and H2[Sr2Nb2ZrO10] related to the Ruddlesden–Popper family of layered perovskite oxides, have been successfully synthesized at room temperature starting from Aurivillius phases Bi2Sr2Nb2MO11.5 (M = Al, Ga) and Bi2Sr2Nb2ZrO12 by the extraction of bismuth oxide sheets using acids. Synthesis of crystalline protonated oxides was also found to be possible under microwave treatment within a short time duration of 5 min. The protonated oxides have been found to undergo facile ion-exchange reactions with an aqueous solution of NaOH or KOH resulting in novel oxides A2Sr2Nb2MO9.5 (A = Na, K; M = Al, Ga) and A2Sr2Nb2ZrO10 (A = Na, K), which could not be synthesized by conventional high temperature solid state synthetic methods. Powder X-ray diffraction patterns confirmed the topochemical nature of the reactions by reflecting changes only in the c-dimensions. Rietveld refinements carried out in the case of K+ ion-exchanged products confirmed their structural similarity...