Jahn-Teller Phase Transitions in Non-Stoichiometric Oxides with Perovskite Structure: Effect of Mechanical Activation

Structure phase transitions in nonstoichiometry oxides with perovskite structure were considered. The microscopic description of cooperative Jahn-Teller transition was suggested and the effects caused by mechanical activation of oxide systems (their conversion into nanostructural state, acceleration of oxidation-renewal reactions and immiscibility) were analized. The correspondence of the theoretical results to the data of experiment on phase states of mechanically activated oxide NdMnO3is shown.

CHARACTERIZATION OF NANOSTRUCTURES IN BULK ALLOYS BY ELECTRICAL RESISTIVITY MEASUREMENTS

The control of nanostructural features such as clusters and precipitates offers tremendous potential for improvements in the properties of advanced alloys. However, due to their inherently small size characterization is a major problem. Techniques such as TEM, AFM, and FIM have sufficient resolution, however they are only able to sample a small volume of what is a bulk material. Other characterization techniques such as XRD and DSC are capable of producing more representative results but still have limitations. Electrical resistivity measurements are extremely simple and have been used to characterize conventional materials for many years. However, as the wavelength of the electrons in the metals is extremely small, the potential use of resistivity measurements for interrogating nanostructural features has not been fully explored. The paper presents how electrical resistivity measurements combined with more conventional techniques can be used to understand the evolution of the nanostructural state in advanced aluminum alloys.