The structure of near stoichiometric Ge-Ga-Sb-S glasses: A reverse Monte Carlo study

Abstract

The structure of Ge 22 Ga 3 Sb 10 S 65 and Ge 15 Ga 10 Sb 10 S 65 glasses was investigated by neutron diffraction (ND), X-ray diffraction (XRD), and extended X-ray absorption fine structure (EXAFS) measurements at the Ge, Ga and Sb K-edges. Experimental data sets were fitted simultaneously in the framework of the reverse Monte Carlo (RMC) simulation technique. Short range order parameters were determined from the obtained large-scale configurations. It was found that the coordination numbers of Ge, Sb and S are around the values predicted by the Mott-rule (4, 3 and 2, respectively). The Ga atoms have on average 4 nearest neighbors. The structure of these stoichiometric glasses can be described by the chemically ordered network model: Ge-S, Ga-S and Sb-S bonds are the most important. Long Sb-S distances (0.3 -0.4 Å higher than the usual covalent bond lengths) are observed, suggesting that Sb atoms can be found in various local environments. 15-16 groups of the periodic table, the total coordination number of the elements (N i ) follows the Mottrule [36]: It is equal to 8-N, where N is the number of electrons in the valence shell of the ith element (e. g. Ge-As-Se [37], Ge-As-Te [38], Ge-Sb-Se [39], Ge-Sb-Te [40]). However glasses containing group 13 elements can deviate from this rule, and the total coordination number of Ga or In can be four instead of three [41 -44]. The structure of several chalcogenide glasses can be described in the framework of the chemically ordered network model (CONM) [45, 46]. This model predicts that M-Ch bonds are preferable, where M denotes the elements from groups 13, 14 or 15, and Ch means the chalcogen element. The structure of the stoichiometric glass can be built from tetrahedral and/or pyramidal units such as [GeCh 4/2 ] or [SbCh 3/2 ]. The M-M and Ch-Ch bonds are present only in non-stoichiometric glasses: M-M bonds in Ch-deficit (Ch-under stoichiometric) compositions and Ch-Ch bonds in Ch-rich (Ch-over stoichiometric) glasses.preparing Ge 22 Ga 3 Sb 10 S 65 and Ge 15 Ga 10 Sb 10 S 65 , i.e. 5N for germanium, gallium, antimony or sulphur.Commercial sulphur was further purified by successive distillations to remove carbon (CO 2 , CS 2 , COS) and hydrates or sulphide hydride (H 2 O, OH, SH) impurities. Then, the required amounts of chemical reagents were put in silica ampoules and pumped under vacuum (10 -4 mbar) for a few hours. The tubes were then sealed and heated at 850°C for 12h in a rocking furnace to ensure the homogenization of the melt. After water quenching, the glass rods were annealed near their glass transition temperatures for 6h. The densities of the samples were determined using a Mettler Toledo XS64 system measuring the weights of the samples in air and water. The density values are shown in Table 1.Neutron diffraction experiments were carried out at the 7C2 diffractometer of LLB (Saclay, France).

Compositional Dependence of Infrared Transmission in Ge‐Based Chalcogenide Glasses

“…[ 26–28 ] Moreover, Ga atom is present in the present quaternary sulfide glasses, which is supposed to be trivalent in its valence state but fourfold coordinated in its local structural environment. [ 29–32 ] Non‐zero electric dipole moment should be involved between the initial and final vibrational states in order for an IR absorption to take place. [ 22 ] As such, the stronger amplitude of the fundamental vibrational absorption in the sulfide glasses seems to result from their enhanced ionicity.…”

Mechanical Alloying and Concentration Quenching of the Luminescence of Pr3+ Ions in Chalcogenide Glass

“…The broadening is presumably caused by a distortion of the structural units, namely, an increased variation in the chemical bond angles M-S-M and S-M-S, where M = Sb(Ge,Ga), due to structural disturbance caused by the introduction of the Pr 3+ ion into the glass matrix, forming an atypically high-coordination environment around itself. Thus, the coordination number in glass for Sb is typically three [22,23], and for Ge and Ga, it is four [23,24]. However, for the lanthanide ion (Pr 3+ ), it ranges from 6 to 9 according to various sources [13,25,26].…”

Structure and Luminescent Properties of Glasses in the GeS2-Ga2S3-Sb2S3:Pr3+ System

“…The Sb-S distances were found in the glass structure, which are 0.3–0.4 Å longer than the length of the covalent bond. On the basis of which, it was suggested that Sb atoms can have different local environments [ 12 ]. The glass formation region, density, refractive index, thermal expansion coefficient, T g of this ternary system were studied in [ 13 ].…”