Synthesis, Crystal Structure, and Physical Properties of Two Polymorphs of CsGaSe2, and High-Temperature X-ray Diffraction Study of the Phase Transition Kinetics

Abstract

The light gray selenogallate CsGaSe2-mC64 was obtained by reaction of stoichiometric amounts of CsN3, GaSe, and Se at elevated temperatures. Its crystal structure was determined by single-crystal X-ray diffraction. The compound crystallizes in the monoclinic space group C2/c (No. 15) with a = 11.043(2) A, b = 11.015(4) A, c = 16.810(2) A, β = 99.49(1) °, V = 2016.7(8) A3, and Z = 16 (powder data, ambient temperature). Its crystal structure features anionic layers ∞2[Ga4Se84–] consisting of corner-sharing Ga4Se10 supertetrahedra. The compound undergoes a first-order phase transition at temperatures of 610 ± 10 °C. The high-temperature phase CsGaSe2-mC16 also crystallizes in the monoclinic space group C2/c (No. 15) with a = 7.651(3) A, b = 12.552(4) A, c = 6.170(3) A, β = 113.62(4)°, V = 542.9(5) A3, and Z = 4 (powder data, ambient temperature). The crystal structure of the high-temperature phase consists of SiS2 analogous chains ∞1[GaSe2–]. In situ high-temperature X-ray diffraction experiments were perfor...