Cation Disorder in Three-Layer Aurivillius Phases: Structural Studies of Bi2−xSr2+xTi1−xNb2+xO12 (0<x<0.8) and Bi4−xLaxTi3O12 (x=1 and 2)

✍ Scribed by C.H. Hervoches; P. Lightfoot

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 322 KB
• Volume: 153
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.2000.8741

✦ Synopsis

The solid solutions Bi 2؊x Sr 2؉x Ti 1؊x Nb 2؉x O 12 (0 < x < 0.6). ( 1) and Bi 4؊x La x Ti 3 O 12 (x ‫؍‬ 1 and 2) (2) have been analyzed in detail by a combination of powder X-ray and neutron di4raction. Both solid solutions adopt a tetragonal variant of the archetypal three-layer Aurivillius phase structure of the parent phase Bi 4 Ti 3 O 12 . The X-ray studies of (1) clearly show that, contrary to earlier assumptions, Sr 2؉ partially substitutes into the [Bi 2 O 2 ] layers, even at the stoichiometric composition Bi 2 Sr 2 TiNb 2 O 12 , the maximum amount of substitution being about 30% at x ‫؍‬ 0.6. The neutron study demonstrates that the Sr 2؉ in this site adopts a signi5cantly more isotropic coordination environment than Bi 3؉ , thus stabilizing this unexpected disorder. The disorder is shown to be driven by the requirement for size matching of the 6uorite-like and perovskite-like layers. A similar level of disorder is found in Bi 2 La 2 Ti 3 O 12 , and this is shown to be due to the requirements for optimum local coordination environment at the La 3؉ /Bi 3؉ sites.