Thermal properties and structures of chlorocadmate, bromocadmate, and bromochlorocadmate glasses

Glass transition temperatures (Tg), crystallization temperatures (Tx), and 113Cd magic-angle spinning (MAS) NMR spectra of the chlorocadmate, bromocadmate, and bromochlorocadmate glasses and the CdCl2, CdBrCl, and CdBr2 crystals have been measured. The Tg and Tx, and thermal stabilities (Tx−Tg) decreased with increasing Br-content. No enhancement of (Tx−Tg) of bromochlorocadmate glasses by anion-mixing was observed. The CdCl2 and CdBr2 crystals gave the isotropic chemical shifts of 183 and −24 ppm, which are assigned to the CdCl6 and CdBr6 octahedra, respectively. The isotropic chemical shifts of CdBrCl crystal (186, 166, 135, 101, 63, 25 and −21 ppm) were assigned to CdBrnCl(6−n) (n=0–6) octahedra, respectively. It was found that the Br and Cl atoms in CdBrCl randomly occupy chlorine sites in the CdCl2 structure. The 113Cd MAS NMR spectra revealed that the chlorocadmate, bromocadmate, and bromochlorocadmate glasses are composed of the CdCl6, CdBr6 and CdBrnCl(6−n) octahedra (n=0–6), respectively, and that the Cd2+ in all the bromochlorocadmate glasses was more preferentially bonded to Br− than Cl−. The relationship between the thermal properties and the anion coordination environments around Cd2+ in these glasses is discussed.