Michael J. Sabochick

A comparison of ferroelectric aging in bulk and thin‐film materials

Thin‐film ferroelectric device researchers have reported that hysteresis loop translation−a characteristic of bulk ferroelectric aging−does not occur in thin‐film devices. This work examines ferroelectric aging in thin‐film materials using a novel measurement procedure that combines the techniques used in bulk and thin‐film testing. The results show that the aging characteristics of thin‐film ferroelectric materials are the same as those exhibited by bulk materials. In addition, the primary and secondary waiting time effects are shown to be directly related to aging.

Atomistic simulation of radiation-induced amorphization of the B2 ordered intermetallic compound NiTi

Amorphization of the B2 intermetallic compound NiTi under electron irradiation has been investigated using molecular dynamics. The effect of irradiation was simulated using two processes: (1) Ni and Ti atoms were exchanged, resulting in chemical disorder, and (2) Frenkel pairs were introduced, leading to the formation of stable point defects and also chemical disorder upon mutual recombination of interstitials and vacancies. After {approximately}0.4 exchanges per atom, the first process resulted in an energy increase of approximately 0.11 eV/atom and a volume increase of 1.91%. On the other hand, after introducing {approximately}0.5 Frenkel pairs per atom, the second process led to smaller increases of 0.092 eV/atom in energy and 1.43% in volume. The calculated radial distribution functions (RDFs) were essentially identical to each other and to the calculated RDF of a quenched liquid. The structure factor, however, showed that long-range order was still present after atom exchanges, while the introduction of Frenkel pairs resulted in the loss of long-range order. It was concluded that point defects are necessary for amorphization to occur in NiTi, although chemical disorder alone is capable of storing enough energy to make the transition possible. 18 refs., 3 figs.

Calculation of defect properties of NiTi and FeTi

The energies and configurations of interstitials and vacancies in the B2 ordered compounds NiTi and FeTi were calculated using atomistic simulation. The stable configuration of a vacancy after the removal of an Ni atom was a vacant Ni site; similarly, the removal of an Fe atom in FeTi resulted in a vacant Fe site. Removal of a Ti atom in both compounds, however, resulted in a vacant Ni or Fe site and an adjacent antisite defect. The effective vacancy formation energies in NiTi and FeTi were calculated to be 1.48 and 1.07 eV, respectively. Interstitials in NiTi formed split {l angle}111{r angle} configurations consisting of a Ni-Ni dumbbell oriented in the {l angle}111{r angle} direction with one or two adjacent antisite defects. The Fe interstitial in FeTi had a similar configuration, except the dumbbell contained Fe atoms. The Ti interstitial in FeTi formed an {l angle}110{r angle} Fe-Fe dumbbell. 8 refs., 2 tabs.

Computer Simulation Study of the Effect of Defects on Switching in Ferroelectric Thin Films

A new computational method for simulating the dynamics of switching in ferroelectric materials is presented. The new method is shown to be more realistic for dynamic simulations and computationally more efficient than the traditional Monte Carlo method. The method is used to investigate the effect of polar defects on switching behavior. The results are in qualitative agreement with experimental observations of fatigue.

Energetics and configurations of lattice defects in CuTi

The energies and configurations of interstitials and vacancies in the ordered compound CuTi were calculated using atomistic simulation. Vacancies created by the removal of either a Cu for Ti atom resulted in a vacant Cu site, with and antisite defect in the latter case. The vacancy at the Cu site was found to be very mobile within two adjacent (001) Cu planes, resulting in two dimensional migration. Interstitials created by inserting either a Cu or Ti atom had complicated configurations containing one or more antisite defects. 11 refs., 1 fig., 1 tab.