Damage from Coexistence of Ferroelectric and Antiferroelectric Domains and Clustering of O Vacancies in PZT: An Elastic and Raman Study

It is often suggested that oxygen vacancies (V O ) are involved in fatigue and pinning of domain walls in ferroelectric (FE) materials, but generally without definite evidence or models. Here the progress of damage induced by the coexistence of FE and antiferroelectric (AFE) domains in the absence of electric cycling is probed by monitoring the Young’s modulus, which may undergo more than fourfold softenings without significant changes in the Raman spectra, but may end with the disaggregation of PZT with ∼5% Ti. At these compositions, the FE and AFE phases coexist at room temperature, as also observed with micro-Raman, and hence the observations are interpreted in terms of the aggregation of V O at the interfaces between FE and AFE domains, which are sources of internal electric and stress fields. The V O would coalesce into planar defects whose extension grows with time but can be dissolved by annealing above 600 K, which indeed restores the original stiffness. The observed giant softening is interpreted by assimilating the planar aggregations of V O to flat inclusions with much reduced elastic moduli, due to the missing Zr/Ti−O bonds. A relationship between the coalescence of a fixed concentration of V O into planar defects and softening is then obtained from the existing literature on the effective elastic moduli of materials with inclusions of various shapes.

Peculiarities of Non-Equilibrium Critical Behavior for 3D Diluted Ising Model with Evolution from Low-Temperature Initial State

The Monte Carlo description of aging properties in nonequilibrium critical behaviour of 3D site-diluted Ising model is considered with evolution from ordered initial state with wide range of spin concentrations. At first, it was shown, that pinning of domain walls on defects leeds to a sharp change of aging properties in diluted systems in comparison with pure system. Therefore, the asymptotic value of the fluctuation-dissipative relation becomes equal to null for diluted systems, while for pure system = 0.784(5).

Investigation of Magnetic Behavior of SmCo5/SmCo2 Nanocrystalline Magnets

Nanocrystalline magnets (SmCo5)94(Cr3C2)6 were prepared using melt-spinning and their magnetic behaviors were investigated by studying their structures and magnetic properties. The alloys prepared using rapid solidification consisted of SmCo5 matrix phase, MgCu2-type SmCo2 secondary phase, and small traces of Sm2Co7 phase. The solidification with higher wheel speed were found to be preferable for the formation of single SmCo2 secondary phase. Relatively high coercive values of 28–36 kOe and high reduced remanence of 0.78–0.79 were observed for the SmCo5/SmCo2 nanocrystalline magnets. The shape of the corresponding magnetization curves revealed that two magnetization processes, nucleation and pinning of domain walls, took place in these magnets. The Henkel plots indicated strong inter-grain exchange coupling effect in these ribbons, consequently resulted in the phenomena of domains interacting with each other and enhancement of the remanence in the ribbons.