Brian L. Cushing

A two-step ion exchange route to the new metastable double-layered perovskite, (Rb,Na)1−xCax/2LaNb2O7 (x ≈ 0.9)

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

Divalent ion exchange of alkaline-earth cations into the triple-layered perovskite RbCa2Nb3O10

Abstract Ion exchange reactions between the Dion-Jacobson-type, triple-layered perovskite RbCa 2 Nb 3 O 10 and calcium, strontium, and barium cations were investigated. Exchange occurs in all systems, but only the strontium and barium systems form stable compounds. The final products, Rb 1−x Sr x/2 Ca 2 Nb 3 O 10 (x = 0.45) and Rb 1−x Ba x/2 Ca 2 Nb 3 O 10 (x = 0.55), are isostructural with the parent. Unit cells contract upon replacement of rubidium with the smaller, more highly charged cation. The effect of layer contraction in directing the extent of exchange is discussed.

IMPROVED SYNTHETIC ROUTES TO LAYERED NAXCOO2 OXIDES

Abstract Improved synthetic routes to fourNaxCoO2 (0.52 ≤ x ≤ 1) oxides of varying compositions and structures are presented. A combination of ceramic techniques and oxidative deintercalation reactions were used to access this series. Comparisons are made to previously reported preparative methods and differences in unit cell parameters discussed.

A multivalent ion exchange route to lamellar calcium cobalt oxides, CaxCoO2(x⩽ 0.5)

New and known layered calcium cobalt oxides, CaxCoO2(x= 0.3, 0.35 and 0.5), are made by ion-exchange reactions from sodium cobalt oxide precursors.

Low-Temperature Multistep Topotactic Routes to New Mixed-Valence Perovskites

Multistep topotactic routes are exploited to introduce mixed-valency into mixed-metal oxides at low temperatures (≤ 350°C). A new set of single- and triple-layered perovskites, Na 1-x-y Ca x/2 LaTiO 4 and Na 2-x+y Ca x/2 La 2 Ti 3 O 10 , respectively, has been prepared by a combination of ion exchange and reductive intercalation. The single-layer series are metastable compounds. The magnetic and electronic behavior of the triple-layer titanate is consistent with Anderson localization effects, while those of the single-layer materials are more complex; samples demonstrate “Hurd-like” conductivity and an unusual magnetic response. The details of the synthesis and characterization of these materials are presented and their magnetic and electronic behavior discussed.