Electrical Conduction and Microstructure of Cobalt and Manganese Co-Doped (La0.8Ca0.2)CrO3−δ Interconnect Materials

Abstract

The microstructure, lattice parameters, mechanical properties, and electrical conductivity mechanisms for Co, Mn co-doped (La 0.8 Ca 0.2 )CrO 3Àd have been systematically investigated. In this study, the concept of defect chemistry is used to explain the relationship between the compensation mechanisms and the electrical conductivity. In air, the hole concentration at high oxygen activity (p ¼ 0.2-u) is larger than that at low oxygen activity (p ¼ 0.2-u-2d 1 ). Therefore, the electrical conductivity decreased with increasing Mn-doping level, and the compensation mechanism is significantly dominated by electrical compensation. In 5% H 2 -95% Ar, the transformation temperature occurred in Mn-doped (La 0.8 Ca 0.2 )(Cr 0.9 Co 0.1 )O 3Àd specimens, which indicates that the prevailing compensation mechanism is changed. Above the transformation temperature, the prevailing compensation mechanism changes from electrical to ionic compensation. The effect of atmospheres on fracture toughness and microhardness for specimens is also investigated in this study. It is found that when the specimens were exposed to 5% H 2 -95% Ar at 1000 C, the cracks appeared in Mn-doped (La 0.8 Ca 0.2 )(Cr 0.9 Co 0.1 )O 3Àd specimens. Presumably, the ionic radii were changed and generated stress that increased brittleness and leaded to cracking. With the increase in the Mn-doping level, the degree of cracking was increased. This indicates these materials could not be used as interconnects at high temperature in the reducing atmosphere.

Effects of Plasma-Sprayed La0.7Sr0.3MnO3Coating on Thermally Grown Oxide Scale and Electrical Conductivity of Fe-Cr Interconnect for SOFCs

“…[1][2][3][4][5] The high temperature operation over 800 • C limits the materials selection for interconnects, and perovskite LaCrO 3 -based ceramics are the most common material despite their high cost. [1][2][3] Recent progress in materials and fabrication techniques in SOFC have allowed for a reduction in operating temperatures to the intermediate ranges of 700-800 • C where low cost Fe-Cr alloys are considered as a potential interconnect material. Traditional ferritic stainless steels with a Cr content of 16-25 wt% create a dense Cr 2 O 3 or chromia-rich scale in an oxidizing environment at elevated temperatures.…”

“…The interconnect materials should have high electrical conductivity, gas tightness and thermal stability in both oxidizing and reducing gas environments. [1][2][3][4][5] The high temperature operation over 800 • C limits the materials selection for interconnects, and perovskite LaCrO 3 -based ceramics are the most common material despite their high cost. [1][2][3] Recent progress in materials and fabrication techniques in SOFC have allowed for a reduction in operating temperatures to the intermediate ranges of 700-800 • C where low cost Fe-Cr alloys are considered as a potential interconnect material.…”