Synthesis, growth and structural properties of (Cu1−xAgx)7GeSe5I solid solutions

Abstract.

Purpose. The purpose of this work was synthesis and crystal growth, X-ray diffraction studies, investigating the compositional behavior of the lattice parameter and the density of (Cu1−xAgx)7GeSe5I solid solutions.
Methods. Single crystals of quaternary compounds with argyrodite structure Cu7GeSe5I, Ag7GeSe5I and solid solutions on their basis (Cu1−xAgx)7GeSe5I with x = 0; 0.25; 0.5; 0.75; 1 were grown by direct crystallization (Cu7GeSe5I, Ag7GeSe5I) and zone crystallization ((Cu1−xAgx)7GeSe5I) from the melt using a modified method. Structural studies were carried out by the methods of differential thermal analysis (chromel-alumel thermocouples, heating and cooling speed 700 K/h) and X-ray phase analysis (DRON 4-07, CuKα radiation, scan angle speed 2Θ – 0.02 deg, exposure – 1 s).
Results. In order to establish near-optimal technological regimes for the growth of single crystals as both individual compounds of Cu7GeSe5I та Ag7GeSe5I, and solid solutions on their basis (Cu1−xAgx)7GeSe5I they were investigated by the method of differential thermal analysis. The diffraction patterns of Cu7GeSe5I and Ag7GeSe5I compounds are indexed in a face-centered cubic lattice. The number and nature of the reflexes on diffractograms of solid solutions indicate that a continuous series of solid solutions is formed in the system. The compositional dependence of the lattice parameter was constructed, which is described by Vegard law. As the content of silver increases, a linear increase in the cubic lattice parameter and a nonlinear increase in density are observed.
Conclusions. Synthesis and growth of single crystals of (Cu1−xAgx)7GeSe5I solid solutions was performed. The growth was carried out by the methods of direct crystallization (Cu7GeSe5I, Ag7GeSe5I) and zone crystallization (Cu1−xAgx)7GeSe5I from the melt using a modified method. According to the results of X-ray diffraction studies, it is established that in Cu7GeSe5I – Ag7GeSe5I system a continuous series of solid solutions is formed. The compositional dependences of the lattice parameter and density are constructed. It was found out that with increasing silver content, a linear increase in the cubic lattice parameter and a nonlinear increase in density in (Cu1−xAgx)7GeSe5I solid solutions are observed

Keywords: solid solutions, synthesis, growth, diffractogram, lattice parameter

10.24144/2415-8038.2019.45.7-13