Thiospinels AIn2S4 (A= Mn, Fe): New synthesis method and structural characterization using X-Ray Powder Diffraction and Raman spectroscopy

J. P. BOLLETTA; J. M. DE PAOLI

La Plata, Buenos Aires

Taller; Fourth MathCryst School in Latin American; 2014

The International School on Fundamental Crystallography

Ternary chalcogenides with spinel crystal structure have been synthesized for the last 60 years using complex methodologies and synthesis lasting up to a month. These systems are interesting due to the change in the interaction between ions and covalency of bonds when compared to oxides with the same structure. Spinels with formula AIn2S4 (A= Mn, Fe) are semiconductors with a large band gap (~2.0 eV), showing antiferromagnetic interactions at low temperatures (below 100 K). However, these properties are highly dependent on the morphology, synthesis method and also the degree of inversion obtained. This degree of inversion measures the distribution of cations between tetrahedral (T) and octahedral (O) sites, and is defined as x in (A1-xInx)T(AxIn2-x)OS4. Polycrystalline samples of thiospinels AIn2S4 (A= Mn, Fe) have been synthesized from stoichiometric mixtures of the corresponding binary sulfides, using a constant gas flow of 1% H2 in Ar, at 1073 K for periods between 6 and 24 hours. From X-ray powder diffraction data it is known that samples achieved over 98% purity in both cases. In addition, their crystal structures were refined using Rietveld analysis, finding cubic unit cells belonging to the Fd-3m space group. Different degrees of inversion where obtained for each structure, namely 0.26 for MnIn2S4 and 0.98 for FeIn2S4. These values of x were confirmed by Raman spectroscopy.