A two-step ion exchange route to the new metastable double-layered perovskite, (Rb,Na) 1−xCa x/2LaNb 2O 7 (x ≈ 0.9)

• Published in: Materials research bulletin Vol. 34; no. 2; pp. 271 - 278
• Main Authors: Cushing, Brian L, Wiley, John B
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 1999
• Subjects: A. layered compounds; A. oxides; B. chemical synthesis; C. differential scanning calorimetry (DSC); C. X-ray diffraction; A. oxides; C. differential scanning calorimetry (DSC); C. X-ray diffraction; B. chemical synthesis; A. layered compounds
• ISSN: 0025-5408; 1873-4227
• DOI: 10.1016/S0025-5408(99)00009-4

A new metastable double-layered perovskite, Rb 0.04Na 0.08Ca 0.44LaNb 2O 7, has been synthesized by a two-step ion exchange route. Initially, RbLaNb 2O 7 is reacted to produce the known metastable phase NaLaNb 2O 7; then this is exchanged with calcium to yield the title compound. The product has neither the RbLaNb 2O 7 nor NaLaNb 2O 7 structure types, but converts to a superstructure of KLaNb 2O 7 with an orthorhombic unit cell: a = 3.885(1), b = 7.725(2), and c = 20.884(4) Å. Direct calcium exchange of RbLaNb 2O 7 results in poorly crystalline products with only 31% exchange, while exchange with KLaNb 2O 7 shows little evidence of reaction. The importance of size matching in divalent-for-monovalent cation exchange is discussed.