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The results of etch-pit and diffraction topographic studies on ammonium dihydrogen phosphate (ADP) are reported. These studies were carried out on specimens sectioned by abrasive wheel and string-saw from large single crystals grown from aqueous solution. The two characterization methods are shown to be in approximate one-to-one correspondence in the case of sections produced by abrasive sawing. Absence of both etch pits and topographic images in sections made by string-sawing of material well removed from the seed region is taken to indicate that this material is dislocation-free. Preliminary results on the plasticity of ADP are reported.

Tho I!;ro\\"ing of large single crystals of hi gh quality from solution requ ires t he p~• e cise control of s upersat uration a nd t he avoida ncc of t hermal and m echal1lcal shock. Ul1Iform arowth conditions a nd cleanliness need to be maintained. Good seed crystals a re necessary ~lld the accidental int rodu ction or generation of new nuelei should be prevent.ed insofar as possible. In the apparatus and eq uipment assembli es here describcd , t he cr ystal-growth bath is d esigned for uniform growth conditions a nd the exclusion of co ntam ination. The s upport [or t he cr ystals provides for convenient mo unting of t he secds, h olds Lhe cr ystals firml y, an d allows their easy rcmoval with min imum damage. A I~CW rever sin g rotat. ion m echa nism promotes equal wash ing of t he crystal s ur faces and ach lcves unIform te mperatu re and composition of the solu tion without, at t h e same t im e,. prod ucin g .significant mechanical stresses in the crystals. The te mperature controller gi ves r eg ulallOn of the temperature an order of mag ni t ud e more sensitive than those hitherto used and provides for s tepl eR'> cha nge of temperature. The crystals are t hus fr ee. fr om li q uid in clL!s!ons found to rcs ul t from s udden acceleration of growth. The electrolytIC conductanee of lo mc solut ions may be used as a precise and sens iti\•e measure of solution co ncC'ntration and supersat uration. The crystal-growt h procedures whi ch are reported have res ul ted in t he p rodu ctio n of very good single crystals of a cons ide rable variety of chemi cal phases.