Study of the Formation of Bi2Te4O11

• Published in: Journal of solid state chemistry 1996-02, Vol.121 (2), p.251-261
• Main Authors: Szaller, Zs, Pöppl, L., Lovas, Gy, Dódony, I.
• Format: Article
• Language: English
• Subjects: Chemistry; 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; Physics; Preparations and properties; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Water, oxides, hydroxides, peroxides
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1006/jssc.1996.0036

The solid state reaction in a 1:4 mole ratio mixture of Bi2O3and TeO2and the polymorphic phase transition of Bi2Te4O11have been investigated using differential scanning calorimetry (DSC), electron microprobe, X-ray powder diffraction (XPD), and selected area electron diffraction (SAED) analysis in the 25–730°C temperature range. Upon heating first a 8Bi2Te4O11+ 23TeO2eutectic is formed, which melts at 598.9°C. In this melt the excess of Bi2O3reacts further and the Bi2O3+ 4TeO2= Bi2Te4O11reaction takes place. The cubic modification is formed by fast crystallization of the Bi2Te4O11melt. The structure of the cubic Bi2Te4O11can be characterized by the lattice constant ofa= 5.6397(5) Å and space groupFm3m. The main product of a slow cooling is the same cubic polymorph although a subordinate formation of the monoclinic phase is also observed. The β-Bi2Te4O11cubic phase undergoes a monotropic transformation into the α-Bi2Te4O11monoclinic modification at temperatures higher than 400°C. The cubic → monoclinic transition is the result of an ordering in one set of {111} planes and the orthogonality of the cubic phase in the [110] projection changes to monoclinic symmetry. The melting enthalpies of the cubic β-phase and the monoclinic α-phase are 35.9 ± 3.3 J/g and 84.3 ± 4.3J/g respectively.