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

Abstract

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 Sr 3Cu 2O 5Cl, the superconductor identified from scanning SQUID petrographic analysis of the KClO 3+Sr 2CuO 3 diffusion couple quenched from 60 kbar and 950°C [2]. A series of experiments under these P, T conditions using SrCuO 2+SrCl 2+SrO 2 reaction mixtures gave high Meissner fraction phase assemblages containing Sr 3Cu 2O 5Cl and its Ruddlesden–Popper homolog Sr 2CuO 3Cl in a ratio ≤1:2. While diffusion couple reactions were found to be limited by oxygen diffusion kinetics and the involvement of the ostensibly `inert' KClO 3 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.