Structure of Te-rich Te–Ge–X (X = I, Se, Ga) glasses

Abstract

The structure of glassy Te78Ge11Ga11, Te79Ge16Ga5,Te70Ge20Se10 andTe73Ge20I7—promising materials for far infrared applications—was investigated by means ofx-ray and neutron diffraction as well as extended x-ray absorption fine structuremeasurements at various edges. Experimental data sets were fitted simultaneously in theframework of the reverse Monte Carlo simulation technique. Short range order inTe85Ge15 was reinvestigated by fitting a new x-ray diffraction measurement together with availableneutron diffraction and extended x-ray absorption fine structure data. It was found thatTe85Ge15 consistsmostly of GeTe4 structural units linked together directly or via bridging Te atoms. Te is predominantly twofold coordinatedin Te85Ge15,Te70Ge20Se10 andTe73Ge20I7 whilein Te78Ge11Ga11 and Te79Ge16Ga5 the Te coordination number is significantly higher than 2. The Te–Te bond length is2.80 ± 0.02 Å inTe78Ge11Ga11 while it isas short as 2.70 ± 0.02 Å and 2.73 ± 0.02 Å in Te73Ge20I7 and Te70Ge20Se10, respectively. Our results show that the strengths ofGeTe4 (GeTe3I,GeTe3Se) ‘units’ are very similar in all glasses investigated but the connection between these unitsdepends on the third component. Differences in the Te coordination number suggest thatunlike Se or I, Ga does not build into the Ge–Te covalent network. Instead, it forms acovalent bond with the non-bonding p electrons of Te, which results in an increase in theaverage Te coordination number.