Local Perturbation in Bi2CuO4: Hydrothermal Synthesis, Crystal Structure, and Characterization of the New Bi2(Cu1-2 x M x )O4 (M = Bi, Pb)

• Published in: Chemistry of materials 2001-02, Vol.13 (2), p.543-551
• Main Authors: Henry, N, Mentre, O, Boivin, J. C, Abraham, F
• Format: Article
• Language: English
• Subjects: Chemistry; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Elements and non-metal compounds (oxides, hydroxides, hydrides, sulfides, carbides, ...); Exact sciences and technology; Inorganic chemistry and origins of life; Inorganic compounds; Magnetic properties and materials; Magnetically ordered materials: other intrinsic properties; Physics; Preparations and properties; Saturation moments and magnetic susceptibilities; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Water, oxides, hydroxides, peroxides
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm000509t

Two new compounds Bi2(Cu1 - 2 x M x )O4 (M = Bi, Pb) have been hydrothermally synthesized and structurally characterized. Hydrothermal treatment of Bi6O5(NO3)5(OH)3·5H2O, Pb(NO3)2, and CuO mixtures in NaOH solution at 180 °C for a week yielded single crystals having the nonstoichiometric compositions Bi2.08Cu0.84O4 and Bi2Pb0.04Cu0.92O4 depending on the starting mixture. The two compounds crystallize tetragonally, P4/ncc, Z = 4 with a = 8.588(3) Å, c = 5.799(2) Å and a = 8.535(4) Å, c = 5.812(3) Å for Bi2.08Cu0.84O4 and Bi2Pb0.04Cu0.92O4, respectively. The structure refinements based on 157 and 155 independent reflections respectively converged to R1 = 0.036, wR2 = 0.069 and R1 = 0.049, wR2 = 0.121, respectively. The parent compound Bi2CuO4 structure consists of CuO4 square-planar units stacked one on top of another in a staggered manner by Bi3+ ions along the c axis. The (CuO4)8 columns are connected by Bi3+ ions. In these new compounds, two consecutive Cu2+ ions are randomly removed and an M ion (M = Bi3+, Pb2+) occupies the site at the middle of the two copper vacancies and are thus 8-fold-coordinated by oxygen atoms. This involves the presence of a mixed Cu2+/3+ valence state. Magnetic measurements indicated a low-temperature behavior different from that of the solid-state-prepared Bi2CuO4, but very similar to the Bi2CuO4 samples previously hydrothermally synthesized, which have the nonstoichiometric composition Bi2(Cu1 - 2 x Bi x )O4 with an as yet undetected low x value. The present compounds are the first hydrothermally prepared Bi2CuO4-derived oxides whose structures have been fully determined.