Abstract
In this paper we present the results of the study of dielectric and thermal properties of KDP crystals doped with different complex organic and inorganic molecules which decorate different (pyramidal or prismatic) crystal growth sectors. It is shown that the properties of stained and transparent parts of the crystal in comparison with the corresponding parts of the nominally pure crystal are different for KDP crystals grown by means of traditional (slow) and rapid growth technique. The difference of the domain contribution into dielectric constant of the polar phase and its characteristic hysteresis in pure and dyed crystals, transition temperature position, form of the specific heat anomaly are presented and analyzed. The most probable model of incorporation of the complex impurity molecules into KDP structure is proposed.
Highlights
It is well known that KH2PO4 (KDP) crystals represent the most typical hydrogen-bonded ferroelectric with the order-disorder phase transition
The rapid growth technique makes it possible to overcome the blocking effect of impurities and to grow the crystal uniformly so that the final size of the crystal almost does not depend on the initial size of the seed. It is clearly seen in figure 2 that the temperature dependencies of dielectric constant of KDP crystal grown by both methods is quite different for different sectors: curve 1 shows the classical picture for the pyramidal sector of traditionally grown crystal: there is a temperature region in the polar phase where ε has an anomalously high values (“plateau” region); near 90 K ε sharply decreases, revealing the “freezing out” of the contribution of domain walls mobility
We have studied dielectric and thermal properties of KDP crystals doped with dye molecules staining different sectors of growth of crystal matrix
Summary
It is well known that KH2PO4 (KDP) crystals represent the most typical hydrogen-bonded ferroelectric with the order-disorder phase transition. The crystals grown with the rate exceeding 10 mm/day (rapid growth technique [3,4]) start from the point seed and grow uniformly for both prismatic and pyramidal faces since in this case the blocking effect of inevitable solution impurities becomes much smaller and is distributed more uniformly on all faces. It was shown that many other different dyes and complex inorganic molecules can be introduced in the KDP crystal lattice selectively in pyramidal or prismatic sectors [11,12] but no information about thermodynamic properties of the stained and nonstained parts has been reported. The difference in the properties of the “pure” KDP crystals grown by means of traditional and rapid growth techniques is considered as a necessary background for the separation of defects – induced effects [13]
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