Grain determination, conductance changes

The films consist of a number of grains or nanoinclusions, each of which has an individual transition temperature, which leads to the hysteresis loop broadening. If the phase transition temperature could be determined as a point, where the temperature dependence curve has a maximal slope, then in our case it is equal to 58 °C. As a result, the VO2 thin films do not demonstrate a sharp change of electrical conductance characteristics at the phase transition, and the hysteresis is sufficiently large. 

The overall microstructure of the bulk sample following a full creep run at 1620 K was found to have changed little from that observed following the 4-h anneal. No cavitation was observed, In order to determine the reason for the break observed in the creep curve at 1620 K, a careful TEM analysis was conducted on samples taken both before the break in cuve and after, and these were compared to a sample taken from the lower temperature creep run, 1470 K, where no break was observed. The microstructure representing the material before the break was obtained by allowing the material to deform at stresses of 50,100, and 150 MPa with a final true strain of -0.9%. The sample used to represent the microstructure after the break was deformed at stresses of 50,100,150,200,250,300 and 350 MPa with a final true strain of -1.5%. High resolution electron microscopy was used to examine the grain boundaries in each sample. 

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