1 Influence of Alkali Metal Substitution on the Phase 2 Transition Behavior of CsGa Q 2 ( Q = S , Se ) 3

The formation of solid solution series Cs1-xMxGaQ2-mC64 (M = K, Rb; Q = S, Se; x = 0–1) 9 was studied by X-ray diffraction and spectroscopic methods, revealing a complete miscibility of 10 CsGaQ2-mC64 with RbGaQ2 and KGaSe2, and a large miscibility gap with KGaS2. All solid solution 11 members exhibit similar Raman spectra, indicating the covalent Ga-Q bonding character. The 12 similar optical band gaps likewise further contribute to this conclusion. Up to a degree of 13 substitution, these solid solutions undergo a phase transition similar to CsGaQ2-mC64. The influence 14 of the substitution parameter x on phase transition process was investigated in situ using high15 temperature X-ray powder diffraction experiments. Phase-pure solid solutions of the high16 temperature polymorphs Cs1-xMxGaQ2-mC16 were obtained up to xmax(K) = 0.1 and xmax(Rb) = 0.3. 17 The crystal structures of these new CsGaQ2-mC16 analogous high-temperature phases were refined 18 from synchrotron diffraction data by Rietveld-refinement. 19