Topochemical Synthesis of Three-Dimensional Perovskites from Lamellar Precursors

Abstract

A topochemical route to nondefect, three-dimensional perovskites from lamellar Dion-Jacobson and Ruddlesden-Popper precursors was demonstrated. The method involves reduction of one of the ions (in this case Eu 3+ ) in the precursor phase and concomitant loss of oxygen. CsEu 2 Ti 2 NbO 10 , a three-layer Dion-Jacobson compound, was ion-exchanged to AEu 2 Ti 2 NbO 10 (A ) Na, Li) and reduced in hydrogen to form the SrTiO 3 -type perovskites AEu 2 Ti 2 NbO 9 . Similarly, K 2 Eu 2 Ti 3 O 10 , a three-layer Ruddlesden-Popper compound, underwent divalent ion exchange to form the Dion-Jacobson compounds A II Eu 2 Ti 3 O 10 (A II ) Ca, Sr) and M II Eu 2 Ti 3 O 10 (M II ) Ni, Cu, Zn), which were reduced in hydrogen to perovskite-type A II Eu 2 Ti 3 O 9 and M II -Eu 2 Ti 3 O 9 , respectively. The A II and Eu 2+ ions of A II Eu 2 Ti 3 O 9 remain ordered, while A-site disordering occurs in the other perovskites. In all cases, the anisotropic texture of the layered precursors is retained in the product perovskite phase.

Molten Salt Synthesis of Ceramic Powders

“…Typical examples are the conversion of the layered perovskite to perovskite (Schaak & Mallouk, 2000) and the preservation of the packing direction of closed-packed layers. (Zeng et al, 2006).…”

Structural Characterization of New Layered Perovskites MLa2Ti2TaO10 (M=Cs, Rb) and NaLa2Ti2TaO10 ·xH2O (x=2, 0.9, 0)

“…In addition, Aurivillius and R-P phases could be interchanged by the selective leaching of Bi O sheet and metathesis reaction (7,8). Schaak and Mallouk have prepared an A-site ordered 3-D perovskite, CaEu Ti O , from n"3 R-P phase Na Eu Ti O (9). Very recently, we have demonstrated that the B-site cations in Cs¸n Ti NbO (¸n"La, Pr, Nd, Sm) are arranged into the new-type ordering sequence of (Ti Nb )O }TiO }(Ti Nb )O (10).…”

Metastable Sr0.5TaO3 Perovskite Oxides Prepared by Nanosheet Processing

“…[42] The raw materials SrCO 3 , Ta 2 O 5 , and K 2 CO 3 (40 mol-% excess) were thoroughly mixed and calcined at 850°C for 6 h and sintered at 1200°C for 10 h. Ion exchange [43][44][45] (Figure 1a), which was used for synthesizing metastable Sr 0.5 TaO 3 with a threedimensional perovskite structure (Figure 1d). Sr 0.5 TaO 3 powder was prepared by two different processes: (1) direct dehydration of the host material [44,[46][47][48][49][50] and (2) nanosheet processing (Figure 1). In the direct dehydration process, the host material H 2 Sr 1.5 Ta 3 O 10 was dehydrated by heat treatment at 600°C for 2 h in air, which led to Sr 0.5 TaO 3 powder.…”