Structural, thermal behaviour and vibrational study of a new mixed

cesium–ammonium tellurate

WAFA BEN ARIBIA^a, MAKKI ABDELMOULEH^a, VAN DER LEE^b

and AHLEM KABADOU^a,*

^aLaboratoire de Sciences des Matériaux et de l’environnement, Faculté des Sciences de Sfax, Université de

Sfax, BP 1171, 3000 Sfax, Tunisia

^bInstitut Européen des Membranes (UMR 5635), Université de Montpellier II, cc 047, Place E. Montpellier,

France

e-mail: ahlemkabadou@yahoo.fr

Abstract. Synthesis, crystal structure, thermal characterization, FTIR and Raman measurements are given for

a new mixed compound cesium–ammonium tellurate. X-ray study showed that the [Cs_0.92(NH₄)_0.08]₂TeCl₄Br₂

compound crystallizes in the tetragonal space group P4/mnc, with a = 7.452 (1) Å, c = 10.544 (3) Å and

Z = 2. The refinement converged at room temperature to R_p = 0.093 and R_wp = 0.076. The structure is

considered as isolated octahedral . These anions show a 4◦ rotation around the fourfold axis against

the cubic arrangement of the K₂PtCI₆ type structure. The monovalent cations are located between

the octahedra ensuring the stability of the structure by ionic and hydrogen bonding contacts: Cs...Cl/Br and

N-H. . . . . . Cl/Br. A DTA/TGA experiment at high temperature reveals one endothermic peak at 780K for this

compound. At low temperature a transition from phase I to phase II was detected at 213K by DSC. This

transition, confirmed by Raman analysis, can be attributed to an order–disorder phase transition.

Graphical Abstract. [Cs_0.92(NH₄)_0.08]₂TeCl₄Br₂ crystallizes in the tetragonal space group (P4/mnc)

at room temperature and belongs to the tetragonal K₂PtCl₆ type structure.

Keywords. Crystal growth; X-ray diffraction; crystal structure; Raman spectroscopy.