Binary GexS100-x glasses reveal a richness of elastic and chemical phase transitions driven by network topology. With increasing Ge content (x), well-defined rigidity at xc(1) = 19.3(5)% and a stress transition at xc(2) = 24.9(5)% are observed in Raman scattering. In modulated DSC measurements, the nonreversing enthalpy of relaxation at Tg reveals a square-well-like minimum (reversibility window) with window walls that coincide with the two elastic phase transitions. Molar volumes show a trapezoidal-like minimum (volumetric window) with edges that nearly coincide with the reversibility window. These optical, thermal, and volumetric results are consistent with an isostatically rigid elastic phase (intermediate phase, IP) present between the rigidity (xc(1)) and stress (xc(2)) transitions. Complex Cp measurements show melt fragility index, m(x) to also show a global minimum in the reversibility window with m < 20, underscoring that melt dynamics encode the elastic behavior of the glass formed at Tg. The strong nature of melts formed in the IP has an important practical consequence; they lead to slow homogenization (over days not hours) of nonstoichiometric Ge-S batch compositions reacted at high temperatures. Homogenization of chalcogenide melts/glasses over a scale of a few micrometers is a prerequisite to observe the intrinsic physical properties of these materials.

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We investigate the amorphous Ge x S 100−x (with 10≤ x ≤40) system from ab initio simulations. Results show a very good agreement with experimental findings from diffraction and the topology of the obtained structural models is further analyzed and compared with the selenide analogue. Differences emerge however from a detailed Molecular Dynamics analysis showing the ring statistics and the homopolar defects to not evolve similarly. The findings are also connected to Rigidity theory which provides a topological approach to decoding the physics of network glasses, and effect of composition and temperature are analyzed.

Here we show that a new class of glasses composed of heavy metal oxides involving transition metals (V 2 O5-TeO 2 ), can surprisingly be designed from very basic tools using topology and rigidity of their underlying molecular networks. When investigated as a function of composition, such glasses display abrupt changes in network packing and enthalpy of relaxation at Tg, underscoring presence of flexible to rigid elastic phase transitions. We find that these elastic phases are fully consistent with polaronic nature of electronic conductivity at high V 2 O 5 content. Such observations have new implications for designing electronic glasses which differ from the traditional amorphous electrolytes having only mobile ions as charge carriers. PACS numbers: 61.43.Fs Only one element of the Periodic Table (Se) vitrifies at ambient pressure but a large number of glassy alloys can be obtained by combining appropriate elements from Group III, IV and V with Group VI elements (O, S, Se and Te) such as silica (SiO 2 ) or germanium diselenide (GeSe 2 ). In the design of physical, chemical or electrical properties, these base network glasses are then alloyed with appropriate modifiers (e.g. Na 2 O) or additives (AgI) [1]. Molecular structure of the base network glasses is a prerequisite to develop a basic understanding of a structure-property relationship. The optimization of functionalities upon modification with alkali-oxides or electrolyte additives is then realized on an empirical basis, given the fact that the number of possible combinations is infinite. Another challenge is the absence of any precise information on the microscopic origin of the glass-forming ability itself, the resistance towards crystallization and the kinetics of glass transition. Therefore, few attempts have really been made to obtain glasses from important additives such as transition elements. As a result, the latter usually appear as minor additives for selected applications. For instance, Titania (TiO 2 ) with less than one mole percent is used for photo-active applications [2] such as self-cleaning coatings while Chromia (Cr 2 O 3 ) has been used for centuries as a pigment for the green coloring of silicate glasses [3].Can network glasses be realized with large fraction of transition metal-oxides ? This knowledge appears to be essential for new applications that could emerge from detailed compositional studies, which would open an avenue to ultimately tune materials synthesis to specific applications. Here, we study thermal properties of heavy metal oxide glasses (HMO), composed of TeO 2 and V 2 O 5 .Telluria and Vanadia as such are bad glass formers, but, their pseudo-binary alloys form excellent bulk glasses over wide proportions (18%

In this article we report on the thermal properties of the ternary carbide Nb 2 SnC. Its heat capacity, c p , is 75 J/mol K at ambient temperatures and increases to Ϸ115 J/mol K at 1300 K. Analysis of c p measurements in the 4-15 K temperature range yields a Debye temperature of 324 K and a density of states at the Fermi level of 2.66 ͑eV unit cell͒ Ϫ1 . At room temperature, the thermal conductivity is 17 W/m K and it increases to Ϸ31 W/m K at 1500 K. At temperatures greater than 600 K, roughly 85% of the heat is transported by electronic defects ͑i.e., electrons and/or holes͒. The thermal properties of Nb 2 SnC are quite comparable to those of near-stoichiometric NbC x .