Peculiarities of Ga and Te incorporation in glassy arsenic selenides

International audienceEffect of simultaneous Ga and Te addition on the structure of As2Se3 glasses is studied using X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS) and Raman techniques. It is shown that most of As, Se and Te atoms build a covalent network according to their main valences. Three-fold coordinated As atoms form pyramidal structural units, which are connected via bridges of two-fold coordinated chalcogen atoms (Se, Te). On the other hand, coordination of Ga in glassy samples is found to be greater than three, as expected from its valence, increasing with Te content. Some of the As atoms appear to be converted into four-fold coordinated state at low Te concentration, while a fraction of Te and, possibly, Se atoms are thought to exist in a singly-coordinated (terminal) state in the vicinity of Ga in the samples with higher Te concentration

On the problem of relaxation for radiation-induced optical effects in some ternary chalcogenide glasses

We have investigated the influence of high-energy γ-irradiation on the optical transmission spectra of ternary Ge-As-S chalcogenide glasses of the stoichiometric As₂S₃-GeS₂ and non-stoichiometric As₂S₃-Ge₂S₃ systems. A long-wave shift of the fundamental absorption edge is observed for all glasses. Two different components of radiation-induced changes were specified: static (residual) and dynamic (time dependent) ones. The dynamic component is mathematically described by the exponential and power functions in respect to post-irradiation periods. It is shown that quantitative features of the observed self-restoration phenomena in the irradiated glasses are closely related to their chemical compositions and stoichiometry

Peculiarities of valence band formation in As-Ge-Se semiconductor glasses

Peculiarities of valence bands formation in As-Ge-Se semiconductor glasses have been investigated within AsxGexSe₁₋₂x cut of glass forming region by highresolution X-ray photoelectron spectroscopy (XPS). It is shown that compositional dependence of XPS valence band spectra of the investigated glasses correlates well with previously obtained data for constituent glasses of binary GexSe₁₋x and AsxGe₁₋x systems. In particular, increase in х leads to the decrease in the intensity of bands at ~2 eV responsible for Se lp-states. The valley at ~3 eV is filled by electronic states originated from Se-GE and Se-As bonds. An accompanying decrease in the intensity of the band at ~5 eV is explained by a decrease in Se 4p bonding states associated with covalent bonds

Intermediate Phases, structural variance and network demixing in chalcogenides: the unusual case of group V sulfides

We review Intermediate Phases (IPs) in chalcogenide glasses and provide a structural interpretation of these phases. In binary group IV selenides, IPs reside in the 2.40 < r < 2.54 range, and in binary group V selenides they shift to a lower r, in the 2.29< r < 2.40 range. Here r represents the mean coordination number of glasses. In ternary alloys containing equal proportions of group IV and V selenides, IPs are wider and encompass ranges of respective binary glasses. These data suggest that the local structural variance contributing to IP widths largely derives from four isostatic local structures of varying connectivity r; two include group V based quasi-tetrahedral (r = 2.29) and pyramidal (r = 2.40) units, and the other two are group IV based corner-sharing (r = 2.40) and edge-sharing (r = 2.67) tetrahedral units. Remarkably, binary group V (P, As) sulfides exhibit IPs that are shifted to even a lower r than their selenide counterparts; a result that we trace to excess Sn chains either partially (As-S) or completely (P-S) demixing from network backbone, in contrast to excess Sen chains forming part of the backbone in corresponding selenide glasses. In ternary chalcogenides of Ge with the group V elements (As, P), IPs of the sulfides are similar to their selenide counterparts, suggesting that presence of Ge serves to reign in the excess Sn chain fragments back in the backbone as in their selenide counterparts

Amorphous rigidification and cooperativity drop in semi−crystalline plasticized polylactide

Plasticization of amorphous polylactide shifts the glass transition and extends its temperature range of crystallization to lower temperatures. In this work, we focus on how low−temperature crystallization impacts the mobility of the amorphous phase. Plasticizer accumulates in the amorphous phase because it is excluded from the growing crystal. The formation of rigid amorphous fraction is favored by the low crystallization temperature. It reaches values up to 50% in plasticized polylactide. The increase in the content of rigid amorphous fraction coincides with both the increase of free volume quantified by positron annihilation lifetime spectroscopy, and the decrease in the cooperativity length obtained from the temperature fluctuation approach. The drop of cooperativity is interpreted in terms of mobility gradient due to the amorphous rigidification