New superstructures in as-synthesized and in situ heated (Bi, Pb)2Sr2YCu2O8+δ

✍ Scribed by H.W. Zandbergen; W.A. Groen

• Publisher: Elsevier Science
• Year: 1990
• Tongue: English
• Weight: 828 KB
• Volume: 166
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/0921-4534(90)90407-6

✦ Synopsis

Electron diffraction of as-synthesized compounds of the solid solution Bi,_,Pb>r,YCu 2 0 8+6 and the changes in superstructures occurring upon heating in situ are studied. At room temperature the samples with x=0 and x=0.3 show a Bi-type modulation with k=4& for x=0.6 a different type of modulation is observed, which can be described in five-dimensional space with k, = 5.1( 1)6 and kz = 7.7); for x= 1 .O no modulation is observed. The Bi-type of modulation is accompanied by an extra modulation with a wave vector of 8.5a. All compounds have a P-type Bravais lattice with a unit cell of about 0.54,0.54, 3.04 nm. When crystals are heated in situ above about 450°C a 2a,2b,c superstructure is formed, which is superimposed on the diffraction patterns of the Bi-and Pb-type modulations and which remains present when cooled to 20°C. Ex situ heating of these crystals in oxygen at 450°C leads to a disappearance of the 2a,2b,c superstructure.

It is proposed that the superstructure originates in oxygen vacancies ordering as for similar superstructures occurring in YBa,Cu306_a, SrLa3Cu.,012_-d and Sr3LaCu40,2_-6.