THE PHASE DIAGRAM OF THE FeGa2Se4-FeIn2Se4 SYSTEM AND THE CRYSTAL STRUCTURE OF FeGaInSe4

Abstract

The compounds of the MB2X4 type (M-Mn, Fe, Co, Ni, B-Ga, In, Sb, Bi; X- S, Se, Te) exhibit the phenomenon of electron- or optically-controlled magnetism; therefore, they are very promising for creation of lasers, modulators of light, photodetectors and other magnetic fi eld controllable functional devices. Recent studies have shown that the range of functional characteristics of these compounds can be substantially improved and expanded due the changing the composition of these compounds and the obtaining solid solutions of various types of substitution. The abovementioned shows the relevance of researches aimed to obtain and study the properties of solid solutions based on the MB2X4 compounds. The development and optimization of processes for the preparation of new complex phases are based on the data on phase equilibria and thermodynamic characteristics of the corresponding system. The aim of the present study was determining the phase relations in the FeGa2Se4-FeIn2Se4 system. We used the differential thermal analysis (DTA) and X-ray diffraction (XRD) in order to analyze the samples of the system. The temperatures of the thermal effects were determined using a NETZSCH 404 F1 Pegasus differential scanning calorimeter within room temperature and ~1300 K. The phase composition of the powdered samples was identifi ed by powder X-ray diffraction D2 Phaser diffractometer at room temperature. The defi nition and refi nement of the structure, as well as calculation of the unit cell parameters of intermediate alloys, were carried out by the Rietveld method using Topas-4.2 software. It is established that the studied system is quasi-binary, and characterized by the presence of the distectic and eutectic equilibria, as well as the formation of broad areas of solid solutions FeGa2Se4 (α-phase) and FeIn2Se4 (β-phase). β-phase with composition of FeGaInSe4 melts congruently at 1222 K and crystallizes in the trigoinal system: Sp.gr. R3m, а = 0.39290(1) nm, с = 3.8542(6) nm, V =515.28 (15) nm3. Using the powder diffraction data, the occupation of the crystallographic positions in FeGaInSe4 was determined by the Rietveld method. It was shown that the occupation of the crystallographic positions in FeGaInSe4 qualitatively differs from FeIn2Se4. Obtained experimental results can be used for choosing the composition of solution-melt for the growth of the high-quality crystals of intermediate phases which are of interest as magnetic semiconductors.

Keywords

• FeGa2Se4-FeIn2Se4 system
• phase diagram
• solid solutions
• crystal structure of FeGaInSe4
• Rietveld method.