  GexPxS1-2x glasses in the compositional range 0.05 < x < 0.19 have been
synthesized and examined in temperature modulated differential scanning
calorimetry (MDSC) and Raman scattering experiments. Trends in the
non-reversing enthalpy DHnr(x) near Tg show the term to almost vanish in the
0.090(5) < x < 0.135(5) range, and to increase by an order of magnitude at x <
0.09, and at x > 0.135. In analogy to previous results on chalcogenide glasses,
we identify compositions at x < 0.09 to be elastically floppy, those in the
0.090 < x < 0.135 range to be in the intermediate phase, and those at x > 0.135
to be stressed rigid. MDSC results also show the DHnr term ages in the
stressed-rigid and floppy phases but not in the intermediate phase. The
intermediate phase is viewed to be a self-organized phase of a disordered
network. It consists of at least four isostatically rigid local structures;
corner-sharing GeS4, edge-sharing GeS2, pyramidal P(S1/2)3 and
quasi-tetrahedral S=P(S1/2)3 units for which evidence comes from Raman
scattering. The latter method also shows existence of P4S7 and P4S10 molecules
in the glasses segregated from the backbone. These aspects of structure
contribute to an intermediate phase that is significantly narrower in width
than in corresponding selenide glasses.
