Linking Melt Dynamics with Glass Topological Phases in Ge_xP_xSe_100-2x Ternary

We have synthesized homogeneous equimolar Ge_xP_xSe_100-2x ternary glasses over a wide range of compositions 0< x< 26%. 1.5 gram sized samples in evacuated (5mm ID) quartz tube were alloyed at 960 ^oC for 10 days. When Raman spectra taken along the 1 inch long melt column became identical the samples were declared to be homogenous. Homogeneity means the variance of Se along the melt column decreased to ~0.1%. Modulated DSC experiments were undertaken and trends in T_g(x), del C_p(x) and the enthalpy of relaxation at T_g, del H_nr(x), were established. We observe a reversibility window in the 9%<x<18% range fixing the three topological phases; flexible phase 0<x<9%, intermediate phase (IP) 9%<x<18% , stressed-rigid phase 18%<x<26%. The IP of this ternary is the widest of any chalcogenide multicomponent chalcogenide glass system, a feature that could be tied to the existence of the Ethylene like P₂Se(_1/2)₄ local structure besides the QT, Se=P(Se_1/2)₃ and PYR P(Se_1/2)₃ ones. Molar volumes reveal a volumetric window with V_m(x) decreasing in the IP range from the average behavior across all x. Melt fragility index, m(x), measurements show a Gaussian like minimum near m=15 in the center of the IP and increasing to m(x)>20, both in the flexible (x<9%) and stress-rigid (x>18%)