Bi1−xCrxO1.5+1.5x′, 0.05≤x≤0.15: A New High-Temperature Solid Solution with a Three-Dimensional Incommensurate Modulation

• Published in: Journal of solid state chemistry Vol. 156; no. 1; pp. 168 - 180
• Main Authors: Esmaeilzadeh, S., Lundgren, S., Hålenius, U., Grins, J.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01-01-2001; Elsevier
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Incommensaturate crystals; Incommensurate crystals; Inorganic compounds; Physics; Semi-periodic solids; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Water, oxides, hydroxides, peroxides; Inorganic compounds; Incommensurate phases; Electron diffraction; Modulated materials; Transition element compounds; Ultraviolet spectra; Bismuth oxides; XRD; Infrared spectra; Topology; Experimental study; High-resolution methods; Structural models; Valence; Periodic nodal surface; Chromium oxides; Chemical preparation; TEM; Optical absorption; Crystal structure
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1006/jssc.2000.8978

A new metastable solid solution Bi1−xCrxO1.5+1.5x with 0.05≤x≤0.15 was synthesized by quenching Bi–Cr–O melts and structurally investigated using electron microscopy and X-ray diffraction. The oxidation state of Cr was determined to be +VI by thermogravimetry, optical spectroscopy, and magnetic measurements. Infrared spectra indicate for x=0.05 isolated CrO2−4 tetrahedra and also smaller fractions of Cr2O−27 units. The phase exhibits an average structure of the Fm3m fluorite type and a 3D incommensurate modulation, with wave vectors q1=[α, 0, 0]*, q2=[0, α, 0]*, q3=[0, 0, α]*, a=5.6025(3) Å, and α=0.2866(2) for x=0.15, and with the 3+3D superspace group symmetry P:Fm3m:Fm3m. Atomic modulation functions and periodic nodal surfaces were deduced for observed satellite reflections and a commensurate structure model derived for x=0.05. The modulated structure was compared with that of Bi0.78Nb0.22O1.72, with symmetry P:Fm3m:Fd3m.