Piezoelectric study of poling mechanism in lithium niobate crystals at temperature close to the curie point

Using a piezoelectric technique, we show that when cooling a lithium niobate crystal through its curie point, three different mechanisms may lead to the orientation of its spontaneous polarization: the first one is the well known effect of an applied electric field. The second is the effect of a thermal gradient and the third one is related to the existence of a composition gradient. These last two effects are reported for the first time. All these mechanisms are shown to be effective only in a very narrow temperature range, around the Curie point (of the order of 3° C). Possible explanations for the last two effects are finally given and discussed.