International Journal of Inorganic Materials 3 (2001) 1283–1290 Crystal chemistry and phase equilibria of selected SrO–R O –CuO 2 3 x and related systems; R5lanthanides and yttrium a, a a b c a c * W. Wong-Ng , Q. Huang , I. Levin , J.A. Kaduk , J. Dillingham , T. Haugan , J. Suh , a L.P. Cook a National Institute of Standards and Technology ( NIST), A256 MATLS, Ceramics Division, Gaithersburg, MD 20899, USA b BP- Amoco, Naperville, IL, USA c Geology Department, University of Maryland, Maryland, MD, USA Abstract This paper investigates and reviews the trend of phase formation and crystal chemistry of selected series of compounds in SrO–R O –CuO and related systems. Including in this discussion are (Ba,Sr) RCu O , Sr R(Cu,M) O , where M5selected 2 3 x 2 3 61x 2 3 61x representative and transition elements, (Sr,R) Cu O (14–24), Sr R Cu O (212), and Sr R Cu O (122). The subsolidus 14 24 x 22x 11x 2 x 11x 21x 2 z phase relationships in systems with R5La, Nd, Dy, Ho, Y and Yb are also discussed.  2001 Published by Elsevier Science Ltd. Keywords: SrO–R O –CuO ; (Sr; R) Cu O ; Sr R Cu O ; (Ba,Sr) RCu O ; Sr R(Cu,M) O 2 3 x 14 24 x 21x 11x 2 x 2 3 61x 2 3 61x 1. Introduction nide contraction. In the BaO–R O –CuO, systems, the 2 3 phase diagrams near the CuO corner are significantly more Currently there is renewed interest in the high tempera- complex in the systems with larger R; the number of ture superconducting series Ba RCu O (213, R5 phases in the diagram decreases with decreasing size of R 2 3 61x lanthanides and Y) because of new methods of producing in going from La to Er [4]. metallic tapes coated with these materials. The most The primary goals of this project is to investigate the developed methods include the Ion beam assisted deposi- trend of phase diagrams, phase formation and crystal tion (IBAD) and the rolling assisted biaxial texturing chemistry of compounds in SrO–R O –CuO , and related 2 3 x substrates (RABiT) processes. As a result of these de- systems using X-ray and neutron powder diffraction and velopments, the entire family of the 213 phases is of transmission electron microscopy (TEM). Since the X-ray interest, including the Sr-substituted series. While the Sr- powder diffraction technique is most widely used for phase 213 phase, Sr RCu O is not stable in the Sr system characterization, preparation of powder patterns for the 2 3 61x under ambient conditions, it can be stabilized either under powder diffraction file [5] is another goal of study. In this high pressure [1], or when Cu at the basal chain site is paper, the phase diagrams of the SrO–R O –CuO sys- 2 3 x partially or completely substituted by appropriate metals tems (R5Dy, Ho and Yb) will be compared with the [2,3]. reported systems of R5La, Nd, Ho, and the crystal Phase equilibria of the BaO–R O –CuO systems have chemistry and crystallography of several selected series of 2 3 x been reported extensively in the literature, but the SrO– phases will be discussed. R O –CuO systems have received less attention. Since 2 3 x Ba and Sr are both alkaline-earth elements, studies of 1 phase equilibria of the Sr-substituted systems may provide 2. Experimental further understanding of the crystal chemistry of these lanthanide cuprates. Across the lanthanide series, the ionic Samples were prepared using the high temperature solid radius of the lanthanide ions decreases, known as lantha- 1 Certain trade names and company products are mentioned in the text or identified in illustrations in order to adequately specify the experimental *Corresponding author. Tel.: 11-301-975-5791; fax: 11-301-975- procedure and equipment used. In no case does such identification imply 5334. recommendation or endorsement by National Institute of Standards and E-mail address: winnie.wong-ng@nist.gov (W. Wong-Ng). Technology. 1466-6049 / 01 / $ – see front matter  2001 Published by Elsevier Science Ltd. PII: S1466-6049(01)00133-7