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

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• 作者：Daniel Friedrich ; Marc Schlosser ; Arno Pfitzner
• 刊名：Crystal Growth & Design
• 出版年：2016
• 出版时间：July 6, 2016
• 年：2016
• 卷：16
• 期：7
• 页码：3983-3992
• 全文大小：605K
• 年卷期：0
• ISSN：1528-7505

文摘

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) Åp>3p>, and Z = 16 (powder data, ambient temperature). Its crystal structure features anionic layers _stack">∞p class="stack">2p>[Ga₄Se₈p>4–p>] 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) Å, b = 12.552(4) Å, c = 6.170(3) Å, β = 113.62(4)°, V = 542.9(5) Åp>3p>, and Z = 4 (powder data, ambient temperature). The crystal structure of the high-temperature phase consists of SiS₂ analogous chains _stack">∞p class="stack">1p>[GaSe₂p>–p>]. 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.