Glass formation and short-range order in chalcogenide materials: The (Ag2S)x(As2S3)1-x (0 <= x <= 1) pseudobinary tie line

Mercury Thiogermanate Glasses HgS-GeS2: Vibrational, Macroscopic, and Electric Properties

Glasses in the pseudo-binary system (HgS)_x (GeS₂)_1-x were synthesized over the concentration range of 0.0 ≤ x ≤ 0.5. The fundamental glass properties (macroscopic, electric, and vibrational) were studied using differential scanning calorimetry (DSC), direct current (dc) electrical measurements, Raman spectroscopy supported by DFT modeling, and X-ray diffraction. Mercury species in thiogermanate glasses essentially form chain-like (HgS_2/2) fragments substituting bridging sulfur between corner- and edge-sharing GeS_4/2 tetrahedra. This structural evolution results in a significant monotonic decrease of the glass transition temperatures from 480 to 270 °C. The room-temperature dc conductivity changes non-monotonically with increasing HgS content x over a limited range of 4 × 10^-15 to 7 × 10^-13 S cm^-1. The electronic transport in insulating HgS-GeS₂ glasses occurs via extended electronic states. Tetrahedral HgS_4/4 fragments also appear in the glass network with increasing x. Their exact population needs further advanced structural studies using diffraction techniques.

Structure of semiconducting versus fast-ion conducting glasses in the Ag-Ge-Se system

The transition from a semiconductor to a fast-ion conductor with increasing silver content along the Ag x (Ge0.25Se0.75)(100-x) tie line (0≤x≤25) was investigated on multiple length scales by employing a combination of electric force microscopy, X-ray diffraction, and neutron diffraction. The microscopy results show separation into silver-rich and silver-poor phases, where the Ag-rich phase percolates at the onset of fast-ion conductivity. The method of neutron diffraction with Ag isotope substitution was applied to the x=5 and x=25 compositions, and the results indicate an evolution in structure of the Ag-rich phase with change of composition. The Ag-Se nearest-neighbours are distributed about a distance of 2.64(1) Å, and the Ag-Se coordination number increases from 2.6(3) at x=5 to 3.3(2) at x=25. For x=25, the measured Ag-Ag partial pair-distribution function gives 1.9(2) Ag-Ag nearest-neighbours at a distance of 3.02(2) Å. The results show breakage of Se-Se homopolar bonds as silver is added to the Ge0.25Se0.75 base glass, and the limit of glass-formation at x≃28 coincides with an elimination of these bonds. A model is proposed for tracking the breakage of Se-Se homopolar bonds as silver is added to the base glass.

On the structure of biomedical silver-doped phosphate-based glasses from molecular dynamics simulations

First-principles and classical molecular dynamics simulations have been carried out on undoped and silver-doped phosphate-based glasses with 50 mol% P₂O₅, 0–20 mol% Ag₂O, and varying amounts of Na₂O and CaO.

Atomic structure of As(2)S(3)-Ag chalcogenide glasses

(As(0.4)S(0.6))(100-x)Ag(x) glasses (x = 0, 4, 8, 12 at.%) have been studied with high-energy x-ray diffraction, neutron diffraction and extended x-ray absorption spectroscopy at As and Ag K-edges. The experimental data were modelled simultaneously with the reverse Monte Carlo simulation method. Analysis of the partial pair correlation functions and coordination numbers extracted from the model atomic configurations revealed that silver preferentially bonds to sulfur in the As(2)S(3)-Ag ternary glasses, which results in the formation of homoatomic As-As bonds. Upon the addition of Ag, a small proportion of Ag-As bonds (N(AgAs)≈0.3) are formed in all three ternary compositions, while the direct Ag-Ag bonds (N(AgAg)≈ 0.4) appear only in the glass with the highest Ag content (12 at.%). Similar to the g- As(2)S(3) binary, the mean coordination number of arsenic is close to three, and that of sulfur is close to two, in the As(2)S(3)-Ag ternary glasses. The first sharp diffraction peak on the total structure factors of As(2)S(3) binary and (As(0.4)S(0.6))(100-x)Ag(x) ternary glasses is related to the As-As and As-S correlations.