Electrical Conductivity and Thermodynamic Properties of Some Alkaline Earth-Doped Lanthanum Chromites

Abstract

Alkaline-earth doped lanthanum chromites are currently the interconnecting materials of choice for solid oxide fuel cells (SOFCs). Since these materials in SOFC operating conditions are under a large oxygen potential gradient and at high temperature (1273 K), a thorough knowledge of their physical and thermochemical properties is very important. In the present study, the alkaline-earth doped lanthanum chromites La 1−x Sr x CrO 3 (x = 0-0.3) and La 0.7 Ca 0.3 CrO 3 were prepared from complex precursors isolated from the La(NO 3 ) 3 -Cr(NO 3 ) 3 -urea system. The oxide powders were characterized by means of X-ray diffraction (XRD). The DC electrical conductivities of the samples were measured in the temperature range of 295-1273 K in air. The thermodynamic properties represented by the relative partial molar free energies, enthalpies, and entropies of oxygen dissolution in the perovskite phase, as well as the partial pressures of oxygen, have been investigated by the solid electrolyte galvanic cells method coupled with the solid-state coulometric titration technique, within the temperature range of 1073-1273 K and in a reducing atmosphere (10 −5 Pa). The variation of the electrical conductivities and thermodynamic properties with changing oxygen stoichiometry is discussed. The study demonstrates new correlations existing between the structural, electrical, and thermodynamic properties in the doped lanthanum chromites. 5430195-928X/05/0300-0543/0

Preparation, Electrical Conductivity, and Thermal Expansion Behavior of Dense Nd1−xCaxCrO3 Solid Solutions

“…The conductivity data of La 0.7 Ca 0.3 CrO 3 were taken from Chakraborty et al 4 and Tanasescu et al 29 . The electrical conductivity of Nd 0.75 Ca 0.25 CrO 3 is higher than that of La 0.7 Ca 0.3 CrO 3 in Chakraborty et al 4 , and lower than that in reference 29 . However, the conductivity is still sufficient for the interconnect application in SOFCs 3,30 .…”

“… Temperature dependence of the electrical conductivity of Nd 0.75 Ca 0.25 CrO 3 and La 0.7 Ca 0.3 CrO 3 , measured in air. The conductivity data of La 0.7 Ca 0.3 CrO 3 were taken from Chakraborty et al 4 and Tanasescu et al 29 . …”

“…20 Figure 6 compares the electrical conductivity of Nd 0.75 Ca 0.25 CrO 3 and La 0.7 Ca 0.3 CrO 3 oxides. The conductivity data of La 0.7 Ca 0.3 CrO 3 were taken from Chakraborty et al 4 and Tanasescu et al 29 . The electrical conductivity of Nd 0.75 Ca 0.25 CrO 3 is higher than that of La 0.7 Ca 0.3 CrO 3 in Chakraborty et al 4 , and lower than that in reference.…”

Structures and properties of Sr-doped NdCrO3 solid solutions

“…These electrons tend to hop between trivalent and quadrivalent Cr ions. As a result, a typical small polaron system is formed and therefore improves the conductivity remarkably [17]. To a great extent, the electrical conductivity of Nd 1−x Sr x CrO 3 is most likely decided by the concentration of these small polarons [18].…”

Sintering, transport properties and thermal expansion of Cr-deficient Nd0.75Sr0.25Cr1−δO3 solid solutions

“…Research on perovskite-structure interconnect material has mainly been focused on improving electrical conductivity, sinterability and thermal expansion compatibility. And alkaline earth metal (AE = Mg, Ca and Sr) doping is proved to be very effective in enhancing electron conduction of LaCrO 3 -based materials [5][6][7][8]. However, an issue that cannot be neglected is two structural phase transitions of this material occurred at about 300 and 530 K, respectively [9].…”