Changes In Intermediate Range Order Research Articles

High Precision Detection of Change in Intermediate Range Order of Amorphous Zirconia-Doped Tantala Thin Films Due to Annealing.

Understanding the local atomic order in amorphous thin film coatings and how it relates to macroscopic performance factors, such as mechanical loss, provides an important path towards enabling the accelerated discovery and development of improved coatings. High precision x-ray scattering measurements of thin films of amorphous zirconia-doped tantala (ZrO_{2}-Ta_{2}O_{5}) show systematic changes in intermediate range order (IRO) as a function of postdeposition heat treatment (annealing). Atomic modeling captures and explains these changes, and shows that the material has building blocks of metal-centered polyhedra and the effect of annealing is to alter the connections between the polyhedra. The observed changes in IRO are associated with a shift in the ratio of corner-sharing to edge-sharing polyhedra. These changes correlate with changes in mechanical loss upon annealing, and suggest that the mechanical loss can be reduced by developing a material with a designed ratio of corner-sharing to edge-sharing polyhedra.

Pressure-induced structural change of intermediate-range order in poly(4-methyl-1-pentene) melt

High-pressure in situ x-ray diffraction and specific-volume measurements on isotactic poly(4-methyl-1-pentene) melt have uncovered abrupt changes in the pressure dependence of microscopic structure as well as that of macroscopic density. The first sharp diffraction peak of the polymer melt, which is related to the intermediate-range order and is explained as resulting from the correlations between main chains, is suppressed at pressures less than 1 kbar. These changes in intermediate-range order show similarities to those seen in liquid-liquid or amorphous-amorphous transitions in simpler small molecule based systems, suggesting that this kind of phenomenon may occur in a wide range of materials.

Structural evolution during the sub-Tg relaxation of hyperquenched metallic glasses

We report the structural characteristics during the sub-Tg relaxation in hyperquenched La55Al25Ni20 glasses. The sub-Tg relaxation is associated with the structural change in intermediate range order, as manifested by the appearance of a prepeak in the x-ray diffraction spectrum. Such structural change could be the source of the Johari–Goldstein relaxation in metallic glasses. The mechanism governing the evolution of the prepeak is different between the glasses with the fictive temperature below 604 K and those above 604 K. Cooperative motion of atoms in La-centered clusters was further discussed in terms of the atomic bond deficiency model.

Density fluctuations in the network structure of AgI doped AgPO3 glass: The origin of the phonon-fracton crossover?

Neutron diffraction studies of AgI doped AgPO3 glasses show the growth of a sharp diffraction peak at Q ≈ 0.7 Å −1 with increasing salt content, indicative of a change in intermediate range order. We show that this peak is due to local density fluctuations in the network of PO4 tetrahedra caused by the requirement to maintain connectivity while decreasing the average density. The phosphate backbone shows an inhomogeneous density distribution over regions of diameter ≈ 16 Å within which the number of atoms in a sphere of radius R increases at a rate lower than R3. It is proposed that this local inhomogeneity is related to the observation of a "phonon-fracton crossover" in the dynamics of similar glasses.

Heat capacities of liquid SbSe and BiSe alloys

Measurements of heat capacities for liquid SbSe and BiSe alloys were carried out up to 800°C using an adiabatic scanning calorimeter. Anomalous temperature variation of heat capacity was observed for liquid Sb 0.45Se 0.55, Sb 0.5Se 0.5 and Bi 2Se 3 alloys. Broad maxima were observed in the temperature dependence of their heat capacities. In contrast, the heat capacity for liquid Sb 2Se 3 alloys shows little temperature variation. In the concentration dependence, the maximum of the heat capacity deviates from the stoichiometric composition of M 2Se 3 in both alloy systems. The characteristic behaviour of the heat capacities for liquid SbSe and BiSe alloys can be attributed to a change in intermediate-range order and in local bonding.