Pseudo-quaternary phase relations near Bi 2Sr 2CaCu 2O 8+ x in reduced oxygen pressures

Abstract

Pseudo-quaternary phase compatibilities near Bi 2Sr 2CaCu 2O 8+ x (2212) have been determined between 725°C and 830°C in air, and at reduced oxygen partial pressures to below the decomposition pressure for 2212. The phase stabilities of the component phases in the equilibria were determined over the temperature range 725–830°C and oxygen partial pressure range 1 × 10 −5 atm to 2 × 10 −1 atm. Five decomposition reactions (including the decomposition of 2212) were identified as well as nine secondary reactions. Ten compatibility tetrahedra were determined in air, and twelve more were predicted. These 22 tetrahedra, each with 2212 as a common vertex, form a polygon that contains 2212 within its volume. The single-phase regions of the pseudo-quaternary oxides in equilibrium with 2212 were determined in the 1/2Bi 2O 3SrOCaO plane. Below the oxygen partial pressure for 2212 decomposition, eight independent four-phase equilibria were identified. The Bi 2(Sr,Ca) 3O 6 phase appears in six of these equilibria and is a prominent phase in reduced oxygen pressures.