One of the main tasks of our laboratory is the growth of optical single crystals by the Czochralski method using open resistance-heated furnaces. Important requirements arising from the production point of view are reproducibility of crystal sizes and the elimination of inhomogeneities due to diameter variation. A number of principles have been worked out for diameter control. A generally accepted method is the one based on weight detection of the growing crystal or of the melt (BUNDLE). Such an automatic growth equipment, including an electronic balance was reported by TOBSCH.In our laboratory a simple, relatively cheap and reliable analogue system based on a balance and a programming phantom has been developed enabling the user to grow cylindrically symmetric single crystals of arbitrary shape.The working principle is demonstrated schematically on Figure 1. The crucible and a liquid containing vessel are placed and tared on an upper-pan laboratory balance with optical reading. During the growth process the phantom modelling the crystal of desired shape immerges into the liquid with the same velocity as the crystal rod is pulled from the melt. If the solid phase. formed in unit time and the liquid displaced by the phantom in unit time have equal weight, equilibrium is conserved. In case of too fast or too slow growth an error signal arises on the balance, and after optoelectronic conversion and amplification this is used as a program signal for temperature control of the furnace, along with the signal of the thermocouple. The actual temperature is displayed and the variation of the temperature during the whole automatic growth process is recorded.The cross-section of the phantom (A,) to be used to obtain the desired cross-section of the crystal (Ac) can be determined from the equilibrium condition for given crystal density (&), crucible cross-section (At), melt density (em), vessel cross-section (A"), and liquid density (el) as follows :The system was realized applying a plexi phantom and glycerin as a liquid and very good experiences have been obtained in the growth of TeOz of 22 mm diameter (F~LDvARI et al.) and LiNbOJ of 50 mm diameter. The shape of the crystal is very well reproduced (Fig. 2). This is not influenced by the position of the crucible in the furnace and the furnace construction. These factors have an effect on the shape of the growth front. The immerging of the crystal seed and starting of the growth process require careful1 work, but after automatic growth has set in, and until the process is stopped, only supervising is necessary. Fast temperature changes, for whatever reason they might happen, are eliminated by the thermocouple control, so they are not incumbent upon the balance control system having a much larger time constant.Thecrysta1 diameter isindependent on thepulling speed. Thediameter variation due to feed-back can be minimized by appropriate regulation of the system and in our experiments deviations were less than k0.3 mm.
1923. A3 3. ANNALEN DER PHYSIK. VIERTE FOLUIE. BANI) 70. 1 ) Heidelberger Habilitationsschrift. 2) P. Lenard, tfber ,4usleuchtung und Tilgung der Phosphore durch Licht. I. Sitzungaber. d. Heidelberger Ak. d. Wis9. Math.-Naturw. K1. Abt. A. 1917. 5. Abh. Ehleitung. hnnalen der Fhyeik. IV. ro'ge. 70. 11 1) P. Lenara, Uber Ausleuchtung unrl Tilgung der Phosphore durcli Licht. I. bis IV. Btzungsber. Heidelberger Ak. d. Wiss. Math.-Naturw. Klesse. Abt. A. 1917. 5. u. 7. Abh.; 1918,8. u. 11. Abh. In dieser Untersuchung ist a d alle frahere wichtige Kenntnis iiber die oben erwhhnten Vorgiinge hingewieeen, so daD sich weitere Literaturangaben hier eriibrigen. 2) B. Gudden u. R. Pohl, Ztschr. f. Phys. 2. S. 192. 1920. i'ber das Lcziditen der Pliosphore uszc. 1. Teil. Allgemeine Beobachtnngen. Das Beobaohtungsverfahren. 1) iihnlich den in der Arbeit der Herren Guddeii und P o h l (Ztsehr. f. Phyn. 2. S. 183. 1920) venvendeten Zellen. 1 1 * 1) Der Spicgel konnte nech der Erregung zur Seite geschoben werden. 2) aber den Begriff der vollen Erregung eines Phosphors vergleiche P. Lensrd, tfber Lichtsummen bei Phosphoren. Sitzungsber. d. Heidelberger Ak. d. Wiss. Math.-Naturm. R h~s e . Abt. A. 1912. 5. Abh. S. 16-1) R. Tomaschek, Ann. d. Ph-p. 86. S. 189. 1921. 1) P. Lenerd, ober Ausleuchtung und algung der Phosphore durch Licht. 111. e. e. O., S. 35. Dime Auffaasung Hrn. Lenerds ist nenerdings d m h die Unteranohungen von Hm. Rupp (E. Rupp, Diss. Heidelberg 26. 6. 1022) exprimentell bestiitigt worden. 13*
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