Structural study of amorphous Te 2X (X = Br, I): X-ray diffraction, neutron diffraction and reverse Monte Carlo simulations

Abstract

Reverse Monte Carlo simulations of the Te 2Br 0.75I 0.25 chalcohalide glass structure using high-energy X-ray and thermal neutron diffraction data show that the glass structure consists of finite –Te–Te–Te– and –Te–Br–Te– chain fragments interconnected by 3-coordinated I atoms. The average Te–Te nearest-neighbor coordination is equal to 2.2 ± 1.4, the Te–Te next nearest-neighbor coordination is equal 7.3 ± 2.6 and the Br–Br coordination is equal to 5.6 ± 0.6. Detailed analysis of the coordination numbers, bond-angle distributions, ring statistics and Warren–Cowley parameters of the different models demonstrates that the short-range order of the glass differs from that of crystalline Te 2X (X = Br, I). The presence of long Te–Te bonds (>3.0 Å) typical for liquid Te and crystalline tellurium-rich polytellurides is also established.