Anatomy of high-pressure synthesis reactions in the Sr-Cu-O-Cl system

As part of a systematic investigation of factors influencing the synthesis of single-phase materials at high pressures [1,2], we have studied the preparation of Sr3Cu2O5Cl, the superconductor identified from scanning SQUID petrographic analysis of the KClO3+Sr2CuO3 diffusion couple quenched from 60 kbar and 950 degrees C [2]. A series of experiments under these P,T conditions using SrCuO2+SrCl2+SrO2 reaction mixtures gave high Meissner fraction phase assemblages containing Sr3Cu2O5Cl and its Ruddlesden-Popper homolog Sr2CuO3Cl in a ratio less than or equal to 1:2 While diffusion couple reactions were found to be limited by oxygen diffusion kinetics and the involvement of the ostensibly 'inert' KClO3 oxygen source [2], these bulk synthesis experiments revealed problems due to sluggish solid state kinetics, sample heterogeneity and reaction with the Au container. Chemographic analysis was used to successfully interpret the complex nature of the phase assemblages observed in the experiments. (C) 1998 Elsevier Science B.V.