Acoustic emission from ferroelectric crystals, which is mainly associated with the P-E hysteresis loop during polarisation reversal, has been studied with the general objective of providing reproducible acoustic emission sources which can be used repeatedly to enable studies of the basic physical nature of acoustic emission and hence to enhance its application in non-destructive testing. Acoustic emission phenomena have been observed in several ferroelectric materials, as a function of applied electric field, sample thickness, and sample temperature. The crystals studied have included Pb5Ge3O11, Pb5-xBaxGe3O11 solid solutions, TGS, BaTiO3 and Rochelle salt. Most acoustic emission activity takes place at the approach to the saturation region of the hysteresis loop which is discussed in terms of domain wall movement and coalescence of domains. An interesting feature found in Pb5Ge3O11 and Pb5-xBaxGe3O11 alloys is the existence of an abrupt electric field threshold for the production of acoustic emission above which the emission increases dramatically as the field is further increased. Acoustic emission measurements suggest that this threshold field corresponds with that required to produce the onset of sideways motion of the domain walls. The threshold field has also been found to show a strong dependence upon sample thickness and temperature. Acoustic emission produced by ferroelectric crystals during polarisation reversal provides a powerful new method of studying ferroelectric properties and the polarisation reversal process in ferroelectric materials. In addition this technique can be used as an alternative to optical and electrical methods of making quantitative measurements of the threshold electric field and domain wall dynamics.
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