MELTING OF SR14CU24O41 AT OXYGEN PRESSURES OF 0.0075, 0.021 AND 0.1 MPA

The eutectic and peritectic melting equilibria of the Sr14Cu24O41 phas e have been studied at oxygen pressures of 0.0075, 0.021, and 0.1 MPa. The Sr14Cu24O41 primary phase field was determined using a combinatio n of differential thermal analysis and electron beam microanalysis of quenched liquids. It was found that the incongruent melting of Sr14Cu2 4O41 takes place at 925, 975, and 1032 degrees C at P-O2=0.0075, 0.021 , and 0.1 MPa, respectively. The peritectic melting reaction under all conditions was confirmed to be: Sr14Cu24O41-->SrCuO2+Liquid+O-2. The liquid composition of this melt was found to range from 79.8% (mole fr action, at P-O2=0.0075 MPa) to 83.9% CuO (mole fraction, at P-O2=0.1 M Pa). The copper oxidation state in these liquids, as estimated from th ermogravimetric data, ranged from Cu+1.42 (at P-O2=0.0075 MPa) to Cu+1 .46 (at P-O2=0.1 MPa). The eutectic melting in the SrO-CuO system occu rs at 918 degrees C (mole fraction of 81.7% CuO), 965 degrees C (mole fraction of 85.0% CuO), and 1005 degrees C (mole fraction of 86.7% CuO ) at P-O2=0.0075, 0.021, and 0.1 MPa, respectively. The temperature ra nge of the Sr14Cu24O41 primary crystallization field was found to incr ease from 7 degrees C at P-O2=0.0075 MPa to 28 degrees C at P-O2=0.1 M Pa, but the compositional width remains small (<4%) at all three oxyge n pressures. These data provide important points on the Sr-Cu-O phase diagram. The data are discussed with reference to the growth of Sr14Cu 24O41 crystals. (C) 1998 Published by Elsevier Science B.V.