Structural Transformations in the Fluorinated T* Phase

✍ Scribed by J. Hadermann; A.M. Abakumov; O.I. Lebedev; G. Van Tendeloo; M.G. Rozova; R.V. Shpanchenko; B.Ph. Pavljuk; E.M. Kopnin; E.V. Antipov

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 883 KB
• Volume: 147
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1999.8438

✦ Synopsis

LaHo 0.75 Sr 0.25 CuO 3.9 , representing the intergrowth of rock salt, 6uorite-type slabs, and (CuO 2 )-layers have been 6uorinated using XeF 2 as a soft 6uorinating agent at temperatures ranging from 200 to 4003C. The resulting structures were studied by a combination of X-ray di4raction, electron di4raction, and high resolution electron microscopy. The samples show a complex microstructure with alternating bands of two 6uorinated phases with di4erent structures. Narrow bands (60+100 A s ) of a monoclinic phase (a m ‫؍‬ a(2+5.5 A s , b m ‫؍‬ a(2+5.5 A s , c m ‫؍‬ c ‫؍‬ 12.84 A s , ‫؍‬ 91.43) are formed in an orthorhombic matrix. The formation of the monoclinic superstructure (A phase) is accompanied by an equal anion arrangement within the initially di4erent rock salt and 6uorite-type slabs and by cooperative displacements of the A cations. In the structure of the less 6uorinated B phase, the 6uorite slabs are not a4ected by 6uorination. Fluorine atoms occupy part of the interstitial positions in the rock salt slabs with partial removal of apical oxygen atoms; this lies most probably at the origin of the incommensurate modulation of the B phase.