We used the same methods as for the preparation of proustite crystals (HOLOVE Y et al.), their identification, the investigation of their properties, so far pyrargyrite haa proved to be an analog of proustite. Ag and S were refined by methods described earlier (HOLOVEY et a]), Sb by zone melting. The quality control was done by chemical-spectral analysis. The ingot middle part had contents of 10+ w.% Cr, Ni, Ti, Si, Mg; 10-'I w.% Cu, other impurities have not been discovered after 25 zone runs.The compound synthesis (70-100 g in weight) was carried out from elementary components by a direct method with vibrate mixing. Synthesis regime was read from the P-T state diagram of elementary compounds and T-X diagrams of Ag-Sb, It could be stated that the rate of reaction till to 660 "C is rather small (the relative yield was about 0.4 @;/hour), in connection with it long exposures a t this temperature are necessary. Increasing of the reaction rate with temperatures growing higher than 650 "C is not possible because of the interaction character in the Sb-S system (KEIQHIN, HONEA). Experimental datas are in agreement with literature. Heating above 650 "C often led to explosions. The product of synthesis was cooled in a horizontal container in order to prevent its cracking Sb-S. 30 griStU/T'echnik, Bd. 8. H. 4

Conditions for the preparation of proustite single crystals are reported. For selecting these conditions temperature gradients in the crystallisation zone and in the melt, the rate of moving of the crystallisation front, the radial gradient, tube geometry, stabilisation of temperature, mechanisms of zone travelling, partial pressures were changcd. -Differential-thermal, X-ray, and spectral-chemical analysis were applied to initial substances and final crystal bodies.To dccrcase the influence of spontaneous crystallisation an optimal temperature gradient was applied approaching maximum undercooling a t the liquid-solid interface. -Optically transparent proustite crystals resulted. I n the range from 1 to 12 pm they show 80% transparency. Microhardness was measured along the growth direction which deviated from the c-axis about 25".Es werden die Bedingungen fur die Herstellung von Proustit-Einkristallen mitgetcilt. Um diese zu bestimmen wurden der Temperaturgradient der Kristallisationsund der Schmelzzone, die Geschwindigkeit der Bewegung der Kristallisationsfront, die radialen Temperaturgradienten, die Rohrengeometrie, die Stabilisierung der Temperatur, die Mechanismen des Zonentransports, und Partialdrucke geiindert. -Sowohl die Ausgangssubstanzen wie auch die Einkristalle wurden differential-thermischcn, rontgenographischen und spektralanalytischen Untersuchungen unterzogen. -Um den EinfluB der spontancn Kristallisation zuriickzudrangen, wurde ein optimalcr Temperaturgradient angelegt, der eine maximale Unterkuhlung an der fest-fliissig-Grenzfliiche ermoglichte. -Die gewonnenen Proustitkristallc warcn optisch durchliissig. Im Gebiet von 1 -12 pm erreichen sei eine Durchliissigkeit von 80%. Die Mikrohiirte wurde nur in Richtung der Wachstumsachse gemcssen, die uni 25' von der kristallographischen c-Achsc abwich.

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