AIn2S4(A= Mn-Ni): New synthesis methods and structural characterization

Abstract

Ternary chalcogenides with the spinel crystal structure have been widely studied for the last 60 years. These compounds are more covalent and allow different interactions between ions when compared to corresponding oxides while maintaining the versatility of the spinel structure. Particularly, spinels with formula AIn2S4(A= Mn-Ni) are found to be semiconductors with a large band gap (~2.0 eV), showing mainly antiferromagnetic interactions at temperatures below 100 K. These properties are dependent on the distribution of cations between octahedral and tetrahedral sites in the structure and also on the synthesis method. Syntheses of these compounds have been extensively reported, involving long heating periods of mixtures of elements or binary sulfides inside evacuated quartz ampoules, lasting for up to two weeks or longer. We report two new, faster synthesis methods for polycrystalline samples of indium thiospinels avoiding evacuated ampoules. Polycrystalline FeIn2S4and MnIn2S4samples were synthesized from stoichiometric mixtures of binary sulfides, heating in a constant gas flow of 1% H2in Ar at 1073 K for 6 and 24 hours respectively. Polycrystalline samples of FeIn2S4, CoIn2S4and NiIn2S4have also been synthesized in a piston-cylinder press, from stoichiometric mixtures of the binary sulfides, at a pressure of 3.5 GPa at 1173 K for 1 hour. From x-ray powder diffraction data all crystal structures were refined by means of Rietveld analysis. Refined cell parameters are in agreement with previous reports. Different degrees of inversion were obtained for each sample. NiIn2S4and both FeIn2S4samples are in accordance with previous reports, while MnIn2S4and CoIn2S4differ from reported values [1]. FeIn2S4and MnIn2S4synthesized in H2/Ar flux were characterized by Raman spectroscopy to further assess cation distribution. In addition, their thermal stability in air was tested by Thermogravimetric Analysis (TGA).