Sintering and Properties of Mixed Lanthanide Chromites

Abstract

A variety of strontium-doped lanthanide chromite compositions were synthesized from a mixed lanthanide (Ln) precursor predominantly consisting of La, Nd, Ce, and Pr. Samples were initially analyzed to assess their sintering characteristics. The most promising sintering behavior was observed for samples of the general formula Ln0.85Sr0.15Cr1−zMzO3,Ln0.85Sr0.15Cr1−zMzO3, where M=transitionM=transition metal elements Co, Cu, Ni, and V, and 0.02⩽z⩽0.1.0.02⩽z⩽0.1. For most compositions >90% theoretical density was attained at 1450°C, though a 5 mol % Cu-doped compound could be sintered to high density as low as 1250°C. High density samples were subsequently analyzed with respect to phase stability, thermal expansion, electrical conductivity in air and reducing atmospheres, and dilation at low oxygen partial pressures. Virtually all samples indicated an orthorhombic- to rhombohedral-phase transformation between 750 and 850°C, and nonlinear Arrhenius electrical conductivity behavior with a positive inflection around 650°C indicative of increased carrier concentrations. Both phenomena are related to the influence of the additional A site cations (in particular Ce in the case of increased conductivity at elevated temperatures). Ln0.85Sr0.15Cr0.95Cu0.05O3Ln0.85Sr0.15Cr0.95Cu0.05O3 was the only sample that exhibited linear conductivity behavior and no discernible structure transformation, thought to be related to the precipitation of a Ce0.5Nd0.5O1.75Ce0.5Nd0.5O1.75 second phase. © 2001 The Electrochemical Society. All rights reserved.