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Chapter VII Reactivity at Dislocation….
method. They used water as an etchant and obtained triangular etch pits for 10
second etching time. They also found that as the etching time increased from 10
to 30 sec, the morphology of triangular etch pits changed. Also, they found from
chemical etching that the dislocation density was less in S-R method grown KDP
crystals than for the conventional crystals. Moreover, Ravi et al [50] have
reported rectangular etch pits on (100) planes of deuterated KDP crystals by
unsaturated solution as an etchant and obtained the dislocation density of about
5x10 3 /cm 2 .
Chemical etching technique was used to investigate the dislocation
behaviors on various sectors of KDP crystals grown with low pH values recently
[51]. Chemical etching revealed that pyramid sector of the crystal displayed more
growth defects. A (100) slice with thickness of 5 mm was cut and polished and
subsequently etched by HAC: H2SO4: H2O = 240:1:25, rectangular etch pits were
observed. A Large number of dislocations and etch pits at the trapezi-form
section showed a serious mismatch in the crystals. Earlier, the growth character
of splicing mis-oriented KDP seeds of both single seed and the special growth of
splicing parallel seeds were investigated [52]. The author used chemical etching
to determine the prismatic and z-plate surfaces of the crystals grown by splicing
bulk KDP crystals.
Chemical etching technique has also been used to reveal certain surface
features, for instance, hillocks and etch spirals. When dissolution of the
crystalline surface takes place on wide spread and leaving a few undissolved
specific parts, it forms hillocks having just opposite nature to the etch pits. Gupta
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