We show here conclusively that the internal field originates from nonstoichiometric point defects in LiNbO3 crystals. The switching fields required for 180° domain reversal in congruent crystals [C=Li2O/(Li2O+Nb2O5)=0.484] are ∼4–5 times larger than the switching fields for nearstoichiometric crystals (C=0.498). An internal field of ∼2.5 kV/mm observed in congruent crystals disappears in stoichiometric crystals. The concentration of hydrogen incorporated during crystal growth has no effect on the switching or internal fields. The measured spontaneous polarization, Ps=80±5 μC/cm2 is relatively insensitive to the crystal nonstoichiometry and the hydrogen content.

We grew LiTaO3 single crystals with a composition close to stoichiometry by using a double crucible Czochralski method. The switching field required for 180° ferroelectric domain reversal and the internal fields originating from nonstoichiometric point defects were compared for the stoichiometric and conventional commercially available crystals. The switching fields for the domain reversal in the stoichiometric crystal with a Curie temperature of 685 °C was 1.7 kV/mm. This is about one thirteenth of the switching field required for the conventional LiTaO3  crystals with a Curie temperature near 600 °C. The internal field in the stoichiometric crystal drastically decreased to 0.1 kV/mm.

The plastic deformation of sapphire (a-AI,O,) has been studied under hydrostatic confining pressure at temperatures below the ambient pressure brittle-to-ductile transition temperature. Samples oriented for prism plane slip (Type I samples) were deformed via dislocation slip at temperatures as low as 200°C. Samples oriented for basal slip (Type I1 samples) could be plastically deformed at temperatures as low as 400°C but showed more complicated deformation behavior, inasmuch as the sample orientation also allowed for the activation of basal twinning and two of the three rhombohedral twin systems. The temperature dependence of the critical resolved shear stress ( I~~J ,for basal slip was significantly greater than that for prism plane slip (Bbasal > BpriPmplane), causing the latter system to be the easy slip system below -600°C (basal slip is the easy slip system at elevated temperatures). Type I1 samples deformed primarily by basal twinning in preference to both rhombohedral twinning and basal slip. The different temperature dependence of T , , for basal and prism plane slip is attributed to details of the dislocation core structure; prism plane dislocations, having a large Burgers vector ( lbppl = 0.822 nm), can dissociate into three collinear partials ([bpi = 0.274 nm) separated by relatively low-energy stacking faults, whereas the comparable dissociation of basal dislocations (lbsl = 0.476 nm) produces two noncollinear partials separated by a relatively high energy stacking fault. Thus, dissociation of basal dislocations is most likely restricted to the dislocation core, which is manifested in a higher Peierls stress at low temperatures for basal slip compared to prism plane slip.

Magnetron-sputter-deposited austenitic 330 stainless steel (330 SS) films, several microns thick, were found to have a hardness ∼6.5 GPa, about an order of magnitude higher than bulk 330 SS. High-resolution transmission electron microscopy revealed that sputtered 330 SS coatings are heavily twinned on {111} with nanometer scale twin spacing. Molecular dynamics simulations show that, in the nanometer regime where plasticity is controlled by the motion of single rather than pile-ups of dislocations, twin boundaries are very strong obstacles to slip. These observations provide a new perspective to producing ultrahigh strength monolithic metals by utilizing growth twins with nanometer-scale spacing.

A systematic study of the kinetics of 180°domains as a function of external electric field is presented for Z-cut LiTaO 3 single crystal wafers at room temperature using transient current measurements combined with nondestructive and real-time imaging of 180°domains by light microscopy. The switching time, wall velocity, and nucleation rate follow an exponential behavior with the applied field. A model is proposed which shows that the nucleation and sideways growth of domains play approximately equal parts in determining the switching time. A domain stabilization process occurs on the time scale of a few seconds even at electric fields where the switching time is milliseconds or less. We show that this stabilization process has a strong correlation to the internal fields in the crystal.