Ionic transport and atomic structure of AgI-HgS-GeS₂ glasses

Abstract

Quasi-ternary (AgI)x(HgS)0.5−x/2(GeS2)0.5−x/2 glasses, 10−4≤x≤0.6 were studied over a wide composition range covering nearly 4 orders of magnitude in the mobile cation content. The glasses show a remarkable increase of the ionic conductivity by 12 orders of magnitude and exhibit two drastically different ion transport regimes: (i) a power-law critical percolation at x≲0.04, and (ii) a modifier-controlled conductivity, exponentially dependent on x≳0.1. Using Raman spectroscopy and high-energy X-ray diffraction supported by DFT modelling of the Raman spectra we show that the glass network is essentially formed by corner-sharing CS-GeS4/2 tetrahedra. Mercury sulfide in glasses is dimorphic. The majority of Hg species (70% at x<0.2) exist as two-fold coordinated (HgS2/2)n chains. Silver species have mixed (2I+2S) tetrahedral environment forming either edge–sharing ES-Ag2I2S4/2 dimers or corner-sharing (CS-AgI2/2S2/2)n chains. The relationship between the ionic transport and atomic structure of the glasses is discussed.

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

“…In particular, the published data for equimolar glassy (HgS) 0.5 (GeS 2 ) 0.5 reveals the four-fold mercury fraction f 4F = 0.33 ± 0.04. 14 The last result suggests that the dimensionality of the glassy host pyramidal As 2 S 3 or tetrahedral GeS 2 is rather insignificant for a larger population of four-fold-coordinated mercury Hg 4F .…”

“…This conclusion is also consistent with the total volume of cavities in g-As 2 S 3 (44%) and g-GeS 2 (54%). 14,68 Consequently, the (HgS 2/2 ) n chains in thiogermanates have more available space resulting in larger interchain contact distances and stronger intrachain interactions with a corresponding decrease of the Hg−S first-neighbor separations and higher stretching frequencies. The common trends in the two systems, (i) a red shift of the stretching frequencies with increasing x and (ii) larger FWHMs of the HgS-rich glasses, have two possible origins: (a) agglomeration of (HgS 2/2 ) n chain fragments and (b) the appearance and growth of four-fold-coordinated mercury Hg 4F .…”

“…Mercury thiogermanate glasses are barely known 12,13 except for equimolar (HgS) 0.5 (GeS 2 ) 0.5 . 14 The effect of pyramidal (g-As 2 S 3 ) and tetrahedral (g-GeS 2 ) glassy hosts on mercury(II) sulfide dimorphism is also an open question to be elucidated using Raman spectroscopy and DFT modeling, glass molar and free volume, and thermal and conductivity parameters. The present report will be further completed by structural studies using pulsed neutron diffraction and high-energy X-ray scattering supported by ab initio molecular dynamics.…”

“…Unraveling the mercury-related vibrational features along with macroscopic properties of HgS-GeS 2 glasses is the essential goal of the present contribution. Mercury thiogermanate glasses are barely known , except for equimolar (HgS) 0.5 (GeS 2 ) 0.5 . The effect of pyramidal (g-As 2 S 3 ) and tetrahedral (g-GeS 2 ) glassy hosts on mercury­(II) sulfide dimorphism is also an open question to be elucidated using Raman spectroscopy and DFT modeling, glass molar and free volume, and thermal and conductivity parameters.…”

Bent HgI2 Molecules in the Melt and Sulfide Glasses: Implications for Nonlinear Optics

“…The interactions between AsS3 pyramid and HgI2 monomer are stronger than expected van der Waals forces. The final optimized Hg-S intermolecular distance, 3.04 Å, appears to be intermediate between the sum of the van der Waals radii, 47 (Hg) + (S) = 3.85 Å and the interatomic distances in binary crystalline mercury sulfides 69,70 or mercury thioarsenate and thiogermanate glasses, 53,71 2.30 Å ≤ Hg−S ≤ 2.54 Å. These rather short intermolecular Hg-S distances might possibly be responsible for the observed but not yet identified second neighbor correlations at ≈3.05 Å both in the neutron and X-ray diffraction data, Fig.…”