Structures and visco-elastic properties of potassium tellurite: Glass versus melt

The structure and visco-elastic properties of K₂Te ₄O₉ have been examined as a function of temperature, using neutron scattering and Brillouin light scattering, respectively. The neutron scattering data indicate that the coordination of tellurium by oxygen changes notably once the material is heated above the glass transition temperature. This and the associated decrease in elastic modulus are consistent with converting network building blocks from trigonal bipyramids to trigonal pyramids. The latter form chain-like structures that constitute a liquid characterized by a single relaxation mechanism. Structural relaxation in the liquid results in further decrease of its elastic storage capacity and in a maximum of dissipative losses due to viscous processes. The break-up of the glassy network, which is attributed to a frictionless transformation of building blocks, is distinct from the viscous relaxation of the liquid; their visco-elastic signatures can be observed in separate temperature intervals.