Switching of partially switched KNbO3 single crystals containing cooperatively ordered impurity dipoles |
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Authors: | S G Ingle R N Kakde |
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Institution: | (1) Laximinarayan Institute of Technology, Nagpur University, 440 010 Nagpur, India |
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Abstract: | Switching studies have been carried out in partially switched KNbO3 single crystals by observing switching transients and hysteresis loops. The crystals used contained ordered impurity dipoles
that are active in nucleating domains around them. Partial initial switching was obtained by applying known compressive stress
to the crystal by means of a spring. The partially switched nature was determined by recording the photograph of the crystal
surface. The changed domain structure on the surface gave a clear idea of the extent of partial switching. As the compressive
stress was gradually increased, the crystal showed increased initial mechanical switching through the mechanism of evaporation
of domain walls associated with ordered impurity dipoles. The dipoles then switch systematically converting 90° domains with
polar axes in the plane of plate into 60° domains with polar axes in the perpendicular pseudocubic {001} planes. The initial
switching condition changes the switching characteristics as determined by hysteresis loops and switching transients. The
results are interpreted in terms of domains in the crystal. If the dipole density is quite high, the effect of the dipoles
becomes negligible, and the switching behaviour approximates that of a normal ferroelectric. The switching transients and
the hysteresis loops in the crystals containing cooperatively ordered dipoles are basically different from the ones observed
in normal ferroelectrics. The anomalous behaviour is detrimental to the use of material in device applications. Hence, it
is shown that the switching transients and hysteresis loops provide a ready means of detecting the presence of these ordered
impurity dipoles. |
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Keywords: | Impurity dipoles cooperative ordering switching transients hysteresis loops |
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