PerspectiveApplied Physics

Stressing Ferroelectrics

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Science  06 Apr 2012:
Vol. 336, Issue 6077, pp. 41-42
DOI: 10.1126/science.1220827

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It is an obvious fact that falling objects accelerate due to Earth's gravitational field. It is much less obvious, however, that objects also stretch during free fall. The decay in the gravitational field strength with distance away from Earth's surface means that, during a fall, parts of objects closer to the ground experience a greater force of attraction than those farther away. This difference in attractive force between top and bottom produces a net stretching effect. It is not the field strength that causes stretching; rather, it is the change of field over distance, or field gradient, that matters. In extreme environments, such as those close to black holes, gravitational field gradients can be huge, causing such profound elongation that astrophysicists have coined a specific term, “spaghettification,” to convey the change in shape suffered by objects in these exotic regions of space. In our everyday experience, however, effects resulting from field gradients are not usually strongly noticeable and are generally only considered to produce second-order effects of little consequence. Despite this, on page 59 of this issue, Lu et al. (1) have been able to cause a reversal in the direction of polarization in a ferroelectric material (ferroelectric switching) solely by using the induced gradient of an applied mechanical stress.