Silver thiogallate (AgGaS₂) crystals have unique nonlinear optical properties. The crystals are usually grown from melts with starting composition lying on Ag₂S-Ga₂S₃ section since it is this part of Ag-Ga-S system which provides growth of high quality crystals [1]. It is accepted that there is a solid solution on the basis of AgGaS₂ with existence region ~1-2 mol.% of Ga₂S₃. In this work we consider experiments with directed crystallization of melts with slight deviation from stoichiometric composition of AgGaS₂ (in moles: 48%Ag₂S+52% Ga₂S₃ and 52%Ag₂S+48% Ga₂S₃). Two-zone synthesis procedure from Ag, Ga and S with nominal purity of 99.999% was the same as described in [2]. Synthesis and growth ampoules were sealed under 10^-4 torr. Vertical Bridgman-Stockbarger technique was used for directed crystallization of the melts. Translation rate and axial temperature gradient at crystallization front was 2 mm/day and ~3.5 deg C/mm, respectively. The change of melt composition was calculated for both experiments using measured chemical composition of the solid phase. Also the difference in unit cell parameters and luminescence spectra for AgGaS₂ grown from above described melts was found. We suppose these phenomena are due to different concentration of vacancies in grown crystals. Both monocrystal samples and samples synthesized from elementary Ag, Ga and S were used for thermal analyses. Obtained data suggests that different ways of preparing the samples are responsible for defects concentration and thus for so wide range (70°C) of melting temperatures reported in scientific literature.

References:

1. Feigelson R. S., Route R. K., Recent developments in the growth of chalcopyrite crystals for nonlinear infrared applications, Opt. Eng., 1987, v.26, N2, 113-119.

2. Zhao B., Zhu S., Li Z., Yu F., Zhu X., Gao D., Growth of AgGaS2 single crystal by descending crucible with rotation method and observation of properties. - Chi. Sci. Bull, Vol. 46, No. 23, 2

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