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) Å, b = 11.015(4) Å, c = 16.810(2) Å, β = 99.49(1) °, V = 2016.7(8) Å3, and Z = 16 (powder data, ambient temperature). Its crystal structure features anionic layers ∞ 2 [Ga4Se8 4−] consisting of corner-sharing Ga4Se10 supertetrahedra. The compound undergoes a first-order phase transition at temperatures of 610 ± 10 °C. The hightemperature phase CsGaSe2-mC16 also crystallizes in the monoclinic space group C2/c (No. 15) with a = 7.651(3) Å, b = 12.552(4) Å, c = 6.170(3) Å, β = 113.62(4)°, V = 542.9(5) Å3, 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 performed to study this phase transition. The crystallization kinetics of the phase transitions were studied using Johnson−Mehl−Avrami−Kolmogorov (JMAK) theory for
isothermal crystallization processes. The activation energy of the phase transition was determined using the Arrhenius equation. Furthermore, the compound was studied by vibrational and diffuse reflectance spectroscopy.