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On the formation of liquid inclusions in some solution-grown crystals: (II) potassium dihydrogen phosphate
Mat. Res. B u l l . , Vol. 19, p p . 873-876, 1984. P r i n t e d in t h e USA. 0025-5408/84 $3.00 + .00 C o p y r i g h t (c) 1984 Pergamon P r e s s L t d .
ON THE FORMATION OF LIQUID INCLUSIONS IN SOME SOLUTION-GROWN CRYSTALS: (II) POTASSIUM DIHYDROGEN PHOSPHATE
Wojciech Kolasi~ski Institute of Physics, Technical University of ~ d ~ , ul. Welcza~ska 219, Poland (Received April i,
93-005 ~ed~,
1984; Communicated b y W. B. White)
ABSTRACT The observations of the formation of liquid inclusions in KDP single crystals grown from aqueous solution in static conditions are presented. It was found that the mechanism of creation of inclusions as proposed by Chernov may be applied to understand their morphology.
Introduction In the previous paper (I) the observations of the formation of liquid inclusions in SCF single crystals were presented. The results of an investigation dealing with the capture of inclusions by potassium dihydrogen phosphate (KDP) crystals are reported in the present paper. Single crystal of KDP is an important, well known material for electro-optical light modulators, Q-switches, frequency doublers and parametric generators (2). KOP crystallizes from aqueous solution in ~2m class of the tetragonal system . The crystal is bounded by the dipyramid ~011~ and tetragonal prism ~I00~ . The dipyramid faces are the only active growth faces of these crystals. Any fragment of the crystal can serve as a seed . The most efficient seed is a plate which faces are normal to the most rapid growth direction. The ( 0 1 1 ) plates were usually used as seeds in our l a b o r a t o r y . In this case a major part of crystal belongs to one of the ~I01~ growth sectors. The formation of liquid inclusions in KDP crystals was investigated extensively (3) but the knowledge of mechanisms of capture of mother liquor is still not satisfactory.
Experimental Potassium dihydrogen phosphate solutions were prepared from analitical grade reagent dissolved in distilled water. KDP crys tals were grown on seeds in the same crystallizers as SCF crys873
874
W. KOLASII~SKI
Vol. 19, No. 7
tals. The seeds were cut parallel to the (011) face from large single,crystals. The seed plates had dimensions of about of 2x3x 0.4 cm ~. The seeds were mounted on the nylon thread in such a way that pyramidal face was vertical. The bulk supercooling was equal to about I°C. Results
and discussion
A microscopic observation of the as-grown surfaces of KDP crystals grown from unstirred aqueous solution showed in some cases the appearance of vicinal hillocks at the lower edge of the sample (fig. I ) . Etching of the surface with hillocks suggests their dislocation nature(list of selective etchants and typical etch patterns for KDP crystal faces were given in ! ~ l e Therefore it may be supposed that ation of growth layers at the lower edge of KDP crystal can be due to the spiral growth mechanism. The layers spread from the edge and the onset of liquid inclu sions could be observed at the place where the growth becames unstable. In KDP crystals two types of liquid inclusions were observed: ( i ) long, narrow channels (fig. 2a), (ii) flat inclw............ sions parallel to the step contour (fig. 2b). FIG. I Vicinal hillocks at the lower edge of (011) face of KDP crystal. The arrow indicates the direction of convective flow. The former are similar to those observed in SCF crystals (1) and probaFIG. 2 bly are due to usual cellular instability. .-.Long, narrow inclusions observed on of the step edge. 011~ face.(b)- A typical example of liqThe latter arise as uid inclusions observed in KOP crystals a result of formation grown on ~011) seed plates. of the overhanging layer parallel to the main growing face (fig. 3). In this case the step contour is created by coagulation of vici~al hillocks. Liquid inclOsions trapped under the overhanging layer forms chains arrayed along the direction of the step motion. The subsequent stages of this process may be seen in figs. 4 a-c. The I! dead water region It near upper horizontal face of the crystal causes the growth of the crystal with raised edges (fig. 5~ This narrow strip of deposited material spreads from edge and
~
Vol. 19, No. 7
POTASSIUM DIHYDROGEN PHOSPHATE
875
corners and overgrow the central region trapping inclusions the~.
FIG. 3 Schematic representation of the formation of liquid inclusions in KDP crystals.
FIG. 4 The subsequent stages of the formation of liquid inclusions in KOP crystal.
FIG. 5 KDP crystal with raised edges.
Conclusion Liquid inclusions in KDP crystals are favourably generated as a result of convective movements in unstirred solutions . The mechanism of formation of inclusions as discussed by Chernov (5) may be applied to understand their different morphology.
876
W. KOLASII~SKI
Vol. 19, No. 7
Acknowledgment The author is grateful to Mrs. K. Soli~ska for her assistance with crystal growth experiments. References 1. 2. 3. 4. 5.
W. Kolasinski, Mat. Res. Bull. I__9, 867 (1984). I . I . Kondilenko, P. A. Korotkov and O. N. Koshel', Kvantovaya elektronika Kiev 1__6,68 (1979). W.J.P. Van Eckevort, R. Janssen-Van Rosmalen, H. Klapper and W. H. Van der Linden, J. Cryst. Growth 60, 67 (1982). K. Sangwal, M. Szurgot, J. Karniewicz and W. Kolasi~ski, J. Cryst. Growth 58, 261 (1982). A.A. Chernov in Sovremennaya kristallografiya, Vol. 3. Nauka, Moscow (1980).
ON THE FORMATION OF LIQUID INCLUSIONS IN SOME SOLUTION-GROWN CRYSTALS: (II) POTASSIUM DIHYDROGEN PHOSPHATE
Wojciech Kolasi~ski Institute of Physics, Technical University of ~ d ~ , ul. Welcza~ska 219, Poland (Received April i,
93-005 ~ed~,
1984; Communicated b y W. B. White)
ABSTRACT The observations of the formation of liquid inclusions in KDP single crystals grown from aqueous solution in static conditions are presented. It was found that the mechanism of creation of inclusions as proposed by Chernov may be applied to understand their morphology.
Introduction In the previous paper (I) the observations of the formation of liquid inclusions in SCF single crystals were presented. The results of an investigation dealing with the capture of inclusions by potassium dihydrogen phosphate (KDP) crystals are reported in the present paper. Single crystal of KDP is an important, well known material for electro-optical light modulators, Q-switches, frequency doublers and parametric generators (2). KOP crystallizes from aqueous solution in ~2m class of the tetragonal system . The crystal is bounded by the dipyramid ~011~ and tetragonal prism ~I00~ . The dipyramid faces are the only active growth faces of these crystals. Any fragment of the crystal can serve as a seed . The most efficient seed is a plate which faces are normal to the most rapid growth direction. The ( 0 1 1 ) plates were usually used as seeds in our l a b o r a t o r y . In this case a major part of crystal belongs to one of the ~I01~ growth sectors. The formation of liquid inclusions in KDP crystals was investigated extensively (3) but the knowledge of mechanisms of capture of mother liquor is still not satisfactory.
Experimental Potassium dihydrogen phosphate solutions were prepared from analitical grade reagent dissolved in distilled water. KDP crys tals were grown on seeds in the same crystallizers as SCF crys873
874
W. KOLASII~SKI
Vol. 19, No. 7
tals. The seeds were cut parallel to the (011) face from large single,crystals. The seed plates had dimensions of about of 2x3x 0.4 cm ~. The seeds were mounted on the nylon thread in such a way that pyramidal face was vertical. The bulk supercooling was equal to about I°C. Results
and discussion
A microscopic observation of the as-grown surfaces of KDP crystals grown from unstirred aqueous solution showed in some cases the appearance of vicinal hillocks at the lower edge of the sample (fig. I ) . Etching of the surface with hillocks suggests their dislocation nature(list of selective etchants and typical etch patterns for KDP crystal faces were given in ! ~ l e Therefore it may be supposed that ation of growth layers at the lower edge of KDP crystal can be due to the spiral growth mechanism. The layers spread from the edge and the onset of liquid inclu sions could be observed at the place where the growth becames unstable. In KDP crystals two types of liquid inclusions were observed: ( i ) long, narrow channels (fig. 2a), (ii) flat inclw............ sions parallel to the step contour (fig. 2b). FIG. I Vicinal hillocks at the lower edge of (011) face of KDP crystal. The arrow indicates the direction of convective flow. The former are similar to those observed in SCF crystals (1) and probaFIG. 2 bly are due to usual cellular instability. .-.Long, narrow inclusions observed on of the step edge. 011~ face.(b)- A typical example of liqThe latter arise as uid inclusions observed in KOP crystals a result of formation grown on ~011) seed plates. of the overhanging layer parallel to the main growing face (fig. 3). In this case the step contour is created by coagulation of vici~al hillocks. Liquid inclOsions trapped under the overhanging layer forms chains arrayed along the direction of the step motion. The subsequent stages of this process may be seen in figs. 4 a-c. The I! dead water region It near upper horizontal face of the crystal causes the growth of the crystal with raised edges (fig. 5~ This narrow strip of deposited material spreads from edge and
~
Vol. 19, No. 7
POTASSIUM DIHYDROGEN PHOSPHATE
875
corners and overgrow the central region trapping inclusions the~.
FIG. 3 Schematic representation of the formation of liquid inclusions in KDP crystals.
FIG. 4 The subsequent stages of the formation of liquid inclusions in KOP crystal.
FIG. 5 KDP crystal with raised edges.
Conclusion Liquid inclusions in KDP crystals are favourably generated as a result of convective movements in unstirred solutions . The mechanism of formation of inclusions as discussed by Chernov (5) may be applied to understand their different morphology.
876
W. KOLASII~SKI
Vol. 19, No. 7
Acknowledgment The author is grateful to Mrs. K. Soli~ska for her assistance with crystal growth experiments. References 1. 2. 3. 4. 5.
W. Kolasinski, Mat. Res. Bull. I__9, 867 (1984). I . I . Kondilenko, P. A. Korotkov and O. N. Koshel', Kvantovaya elektronika Kiev 1__6,68 (1979). W.J.P. Van Eckevort, R. Janssen-Van Rosmalen, H. Klapper and W. H. Van der Linden, J. Cryst. Growth 60, 67 (1982). K. Sangwal, M. Szurgot, J. Karniewicz and W. Kolasi~ski, J. Cryst. Growth 58, 261 (1982). A.A. Chernov in Sovremennaya kristallografiya, Vol. 3. Nauka, Moscow (1980).