•Ge–As–Se glasses are characterized by the lack of chemical short range order.•Se–Se bonds can be found in strongly Se-deficient glasses (e.g. Ge33As20Se47).•Ge/As–Ge/As bonds persist in the strongly ...Se-rich region (e.g. Ge10As10Se80).•The nonlinear refractive index correlates with the concentration of ‘wrong’ bonds.
The structure of GexAs10Se90−x (x=10, 17.5, 22.5, 27.5, 30, 35) glasses as well as some other compositions extensively used in infrared optics, e.g. GASIR® (Ge22As20Se58) and AMTIR-1 (Ge33As12Se55) has been investigated by X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) measurements at the Ge, As and Se K-edges. Structural models have been obtained by fitting simultaneously XRD and EXAFS data by the reverse Monte Carlo simulation technique. Unlike other IV–V–VI glasses (e.g. Ge–As–S, Ge–Sb–Te, Ge–Sb–Se, Ge–As–Te) Ge–As–Se glasses are characterized by the lack of preferential bonding and behave as random covalent networks: Ge–Ge, Ge–As or As–As bonds can be found in Se-rich compositions while Se–Se bonding remains in strongly Se-deficient glasses as well.
(Ge(0.2)Se(0.8))(100-x)In(x) and (Ge(0.17)Se(0.83))(100-x)In(x) (x = 0, 5, 10, 15 at.%) chalcogenide glasses have been studied with high-energy x-ray diffraction, neutron diffraction and extended ...x-ray absorption spectroscopy at Ge, Se and In K-edges. The experimental data were modelled simultaneously with the reverse Monte Carlo simulation method. GeSe(4/2) tetrahedra are shown to be the main structural units in the binary and ternary glasses investigated. Indium bonds to the excess Se atoms in the ternary Ge-Se-In glasses. While the majority of In atoms have three Se neighbours, some In atoms may be tetrahedrally coordinated by Se.
The structure of glassy Cu47.5Zr47.5Ag5 has been investigated by neutron diffraction with isotopic substitution, X-ray diffraction as well as with Cu and Ag K-edge extended X-ray absorption ...spectroscopy (EXAFS). Experimental datasets have been fitted simultaneously with the reverse Monte Carlo simulation technique. Nearest neighbor distances and coordination numbers have been determined and compared with those of glassy Cu50Zr50 and Cu47.5Zr47.5Al5. It has been found that the Cu-Cu coordination number drops upon adding Al or Ag to Cu50Zr50. Both Ag and Al prefer Zr to Cu. The total coordination number of Ag is 13.9±0.6 while that of Al is 10.2±1.0 suggesting that in spite of their similar molar volumes the effective sizes of Ag and Al in the CuZr matrix are quite different.
•Structural model of Cu47.5Zr47.5Ag5 was obtained by fitting multiple experimental datasets.•The Cu-Cu coordination number drops upon adding Ag to Cu50Zr50.•Both Ag and Al prefer Zr to Cu.•The effective size of Ag and Al in the CuZr matrix is quite different.
The structure of Ge
20Te
80, Ge
15Cu
8Te
77 and Ge
15Cu
5Te
80 glasses was investigated by diffraction techniques and extended X-ray absorption fine structure measurements. Large structural models ...were generated by fitting experimental data by the reverse Monte Carlo simulation technique. In Ge
20Te
80 glass, both Ge and Te obey the
8
−
N
rule, and the structure is built up of GeTe
4 tetrahedra connected via Te–Te bonding or shared Te atoms connected to two Ge atoms. The coordination number of Te is significantly higher than 2 in Ge
15Cu
8Te
77. The average coordination number of Cu is
3.41
±
1
in this alloy. In Ge
15Cu
5Te
80 glass, Cu binds mostly to Te, while Cu–Cu bonding is significant in Ge
15Cu
8Te
77.
► We study short-range order in Cu–Ge–Te glasses with diffraction techniques and X-ray absorption fine structure measurements. ► In Ge
15Cu
8Te
77, Te does not satisfy the
8
−
N
rule. ► Cu–Cu bonding is significant in the above composition. ► Cu occupies the free space of the host matrix. ► The host Ge–Te network is not distorted by Cu atoms.
The structure of Zr(60)Cu(20)Fe(20) metallic glass has been studied with high-energy x-ray diffraction, neutron diffraction and extended x-ray absorption spectroscopy and modelled with the reverse ...Monte Carlo simulation technique. It is found that Cu and Fe atoms prefer Zr as a nearest neighbour. The mean interatomic distance between Cu/Fe and Zr atoms in the glass is remarkably shorter than the sum of the respective atomic radii. The coordination numbers for Cu/Fe-Cu/Fe pairs are very close to each other, suggesting a regular distribution of Cu and Fe atoms in the Zr(60)Cu(20)Fe(20) metallic glass.
Short- and medium range order glasses of GeTe4-Ag approximate composition have been studied by neutron diffraction, X-ray diffraction and extended X-ray absorption fine structure spectroscopy. ...Chemical correlations have been determined by fitting multiple datasets simultaneously with the reverse Monte Carlo simulation technique. It has been found that Ge atoms remain basically fourfold coordinated by Te while Te atoms have mostly two Ge/Te neighbours. The topology of the GeTe4 host network does not change upon adding Ag. Similarly to binary Ge-Te glasses, neighbouring GeTe4 tetrahedra are predominantly in corner sharing configuration in all investigated GeTe4-Ag compositions. Ag atoms bind mostly to Te and the average total coordination number of Ag does not change significantly with increasing Ag content.
The structure of Ge20Sb10S70, Ge23Sb12S65 and Ge26Sb13S61 glasses was investigated by neutron diffraction (ND), X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) measurements ...at the Ge and Sb K-edges as well as Raman scattering. For each composition, large scale structural models were obtained by fitting simultaneously diffraction and EXAFS data sets in the framework of the reverse Monte Carlo (RMC) simulation technique. Ge and S atoms have 4 and 2 nearest neighbors, respectively. The structure of these glasses can be described by the chemically ordered network model: Ge-S and Sb-S bonds are always preferred. These two bond types adequately describe the structure of the stoichiometric glass while S-S bonds can also be found in the S-rich composition. Raman scattering data show the presence of Ge-Ge, Ge-Sb and Sb-Sb bonds in the S-deficient glass but only Ge-Sb bonds are needed to fit diffraction and EXAFS datasets. A significant part of the Sb-S pairs has 0.3–0.4 Å longer bond distance than the usually accepted covalent bond length (∼2.45 Å). From this observation it was inferred that a part of Sb atoms have more than 3 S neighbors.
•Structural models of GeSbS glasses consistent with multiple datasets are constructed.•Structure of these glasses can be described by the chemically ordered network model.•Ge and S atoms obey the Mott-rule and have 4 and 2 nearest neighbors, respectively.•Long Sb-S bonds were observed, suggesting that SbS5 units may exist in this system.
PDF
