Large (10 to 20 g) macroscopically sound ZnO crystals suitable for preliminary transducer and other studies have been grown hydrothermally at rates of from 10 to 15 mils per day. The factors found to be important in achieving good growth were (1) base concentration of growth solution, (2) temperature difference between dissolving and growth regions, (3) presaturation of growth solution, (4) warm-up procedure, (5) addition of Li+ to the growth solution to suppress dendrite formation, (6) etching to remove seed damage, and (7) nutrient size. Each of the foregoing factors was studied and is discussed.

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Dense large-grain ceramic samples of Ba,YCu,O, have been oxidized at 400" to 500°C in 10 to 30 MPa of oxygen for I to 10 d . The high-pressure treatment has increased the equilibrium content x slightly above 7 but there is no concomitant increase in T,. At x=7.03 the superconducting transition, measured by ac susceptibility, has an onset temperature of -91 K and AT-4 K and no change in lattice parameter is observed. High oxygen pressure increases the rate of oxidation. [

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