Rigidity transitions and molecular structure of AsxSe1-x glasses

T-modulated differential scanning calorimetry measurements on bulk AsxSe1-x glasses show that the glass transition temperature T-g(x) variation at x<0.12 is linear with a slope dTg/dx=4.1 degrees C/at.% As, and the nonreversing heat flow, Delta H-nr(x) almost vanishes in the 0.291(1)<x<0.37(1) composition range. These thermal results analyzed by agglomeration theory and constraint theory suggest that in addition to As(Se-1/2)(3) units, quasitetrahedral Se=As(Se-1/2)(3) units also serve to crosslink Se, chains at x<2/5. The results also suggest that rigidity onsets at r(c)(1)=2.29(1) and the transition to the stressed rigid phase occurs at r(c)(2)=2.37(1), below the chemical threshold at r(ct)= 2.40 (or x=2/5).