Crystal Structures of Ca-Free Pb2Sr2RCu3O8 (R = La, Pr, Nd, Eu, Tb, and Dy) Single Crystals

✍ Scribed by J.S. Xue; J.E. Greedan; M. Maric

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 612 KB
• Volume: 102
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1993.1062

✦ Synopsis

Structures of (\mathrm{Pb}{2} \mathrm{Sr}{2} R \mathrm{Cu}{3} \mathrm{O}{8}) have been determined by single crystal X-ray diffraction. A monoclinic symmetry ((C 2 / m, Z=2)) was found for those crystals with (R=\mathrm{Pr}, \mathrm{Nd}), and (\mathrm{Tb}), orthorhombic ((\mathrm{Cmmm}), (Z=2) ) for (R=\mathrm{La}), and tetragonal ( (P 4 / \mathrm{mmm}, Z=1) ) for (R=) Eu and Dy. The relationship among different crystal symmetries can be understood in terms of different oxygen orderings in the (\mathrm{PbO}) layers driven by the (\mathrm{Pb}^{2+}) lone pair orientation. There is evidence for (a \sim 9 %) deficiency in electron density at the (R=) Eu and Dy sites (and (\sim 4.5 %) for (R=) Tb) which has been confirmed by mass spectroscopy as being due to cation vacancies at these sites. Bond valence sum calculations have been performed to evaluate the strains existing in the crystal structures of (\mathrm{Pb}{2} \mathrm{Sr}{2} R \mathrm{Cu}{3} \mathrm{O}{8}). 1993 Academic Press. Inc.