A layered cuprate derived from the hexagonal 4H-BaCuO2+x structure: Ba36Ca2Cu32O86-x

A new layered cuprate Ba36Ca2Cu32O86-x has been synthesized using high pres sure technique. It crystallizes in an orthorhombic cell with a approximate to 5.7 Angstrom, b approximate to 9.8 Angstrom and c approximate to 45.50 A ngstrom, space group Immm (or Imm2). The high resolution electron microscop y study shows that this original structure consists of oxygen deficient 4H- hexagonal BaCuO2+x layers, interleaved with barium-calcium layers. The prop osed structural model suggests for copper, a pyramidal coordination. This n ew phase is described as the n = 4 member of a new structural family [Ba8Cu 8O20](n)[Ba4Ca2O4]. Different higher n members (n = 7, 10, 13) are observed as defects by HREM. (C) 1998 Elsevier Science B.V. All rights reserved.