Origin of the solid solution in the LiInSe2–In2Se3 system

• Published in: Journal of solid state chemistry Vol. 220; pp. 91 - 96
• Main Authors: Vasilyeva, I.G., Pochtar, A.A., Isaenko, L.I.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.12.2014
• Subjects: Concentration micro-heterogeneity; LiInSe2–In2Se3 system; Substitution solid solution (Li3x−1Inx⎕2)InSe2; LiInSe2–In2Se3 system; Concentration micro-heterogeneity; Substitution solid solution (Li3x−1Inx⎕2)InSe2
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2014.08.013

Techniques of bulk and local analyses were used to characterize the melt-grown single crystals of LiInSe2, where yellow matrix coexists together with extended red areas distributed irregularly. Bulk chemical analysis showed that the average stoichiometry of yellow matrix is close to ideal 1:1:2, but red areas are enriched with In2Se3. An excess In2Se3 is incorporated coherently into the crystal lattice of LiInSe2, forming the substitution solid solution with the general formula (Li1−3xInx⎕2)InSe2 and changing the color from yellow to red. The test crystals with the 50–55% content of In2Se3 were found by the X-ray analysis to be single phase. The differential dissolution technique, measuring the spatial variation of the composition with high resolution, demonstrated that the single phase crystals in the LiInSe2–In2Se3 system might be grown only in a very narrow range close to stoichiometric. Being supersaturated, the heterovalent solid solution phases decompose in the course of cooling, and the concentration micro-heterogeneity occurs in the matrix as the coherent (or incoherent) inclusions of two different types, practically pure selenides of lithium and indium. The origin and scale of the micro-heterogeneity determining the physical properties of LiInSe2 are discussed as a starting point for the development of physicochemical foundations for growing high quality optical crystals. Differential dissolution technique applied for detection of dispersive precipitates in as-grown LiInSe2 single crystals: kinetic curves of the phase dissolution: F is the main phase Li0.96In1.01Se2 (98.9%), secondary minor phases Li2Se (0.1%), In2Se3 (0.9%). [Display omitted] •Phase purity of crystals Li1−3xIn1+xSe2 was examined by a new stoichiographic method.•Breakup of the metastable solid solution with temperature drop was detected.•Dispersive precipitates Li–Se and In–Se of low content result from the breakup.•A crucial role of the precipitates in optical properties of the crystals is shown.•Conditions are given how to grow stoichiometric and single-phase crystals.