Thermal Expansion Studies on Cathode and Interconnect Oxides*

The thermal expansion of La 0.9 Sr 0.1 Cr 1-x M x O 3 (M ‫؍‬ Mg, Al, Ti, Mn, Fe, Co, Ni; 0 < x < 0.1) perovskites has been studied in oxidizing and reducing atmospheres in the temperature range from 50°to 1000°C. Cobalt doping of La 0.9 Sr 0.1 CrO 3 was an effective way of increasing the average linear thermal expansion coefficient (TEC), whereas titanium doping showed a negative effect. No effect on the TECs was observed for the B-site dopants in perovskites with the remaining dopants. Linear thermal expansion behavior was observed in the La 0.9 Sr 0.1 Cr 1-x M x O 3 perovskites with doping of >1 mol% aluminum or 10 mol% cobalt. TECs of La 0.9 Sr 0.1 Cr 0.96 Co 0.02 Al 0.02 O 3 were 10.5 ؋ 10 ؊6 /°C in air, 10.7 ؋ 10 ؊6 /°C under He-H 2 atmosphere (oxygen partial pressure of 4 ؋ 10 ؊15 atm at 1000°C), and 11.8 ؋ 10 ؊6 /°C in H 2 atmosphere.

Section: -(X؉y) Co X Al Y O 3 Perovskite Separatormentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Control of the Thermal Expansion of Strontium‐Doped Lanthanum Chromite Perovskites by B‐site Doping for High‐Temperature Solid Oxide Fuel Cell Separators

Mori

Hiei

Yamamoto

2001

“…However, it is well known that these materials have many problems, including an oxide-ionic leak-current phenomenon of the sintered body in an oxygen potential gradient, 9,10 low mechanical strength, 11,12 poor low-temperature sintering characteristics in air, [13][14][15] and isothermal expansion under reducing atmospheres. 11,16,17 The selection of SrO or CaO, which are conventionally used as dopants on the A-sites in LaCrO 3 perovskites, is of some concern.…”

Section: Introductionmentioning

confidence: 99%

“…Since alkaline-earth-metal-doped (AE ϭ Ca, Sr) LaCrO 3 -based perovskites, with stoichiometric compositions, have excellent chemical stability under oxidizing or reducing atmospheres at high temperatures, 7,8 they are considered to be the most promising materials for use as interconnects in the planar-type SOFC. However, it is well known that these materials have many problems, including an oxide-ionic leak-current phenomenon of the sintered body in an oxygen potential gradient, 9,10 low mechanical strength, 11,12 poor low-temperature sintering characteristics in air, [13][14][15] and isothermal expansion under reducing atmospheres. 11,16,17 The selection of SrO or CaO, which are conventionally used as dopants on the A-sites in LaCrO 3 perovskites, is of some concern.…”

Section: Introductionmentioning

confidence: 99%

Thermal Expansion Behavior of Titanium‐Doped La(Sr)CrO₃ Solid Oxide Fuel Cell Interconnects

Mori

Hiei

2001

La 0.8 Sr 0.2 Cr 0.9 Ti 0.1 O 3 perovskite has been designed as an interconnect material in high-temperature solid oxide fuel cells (SOFCs) because of its thermal expansion compatibility in both oxidizing and reducing atmospheres. La 0.8 Sr 0.2 Cr 0.9 Ti 0.1 O 3 shows a single phase with a hexagonal unit cell of a ‫؍‬ 5.459(1) Å, c ‫؍‬ 13.507(2) Å, Z ‫؍‬ 6 and a space group of R-3C. Average linear thermal expansion coefficients of this material in the temperature range from 50°to 1000°C were 10.4 ؋ 10 ؊6 /°C in air, 10.5 ؋ 10 ؊6 /°C under a He-H 2 atmosphere (oxygen partial pressure of 4 ؋ 10 ؊15 atm at 1000°C), and 10.9 ؋ 10 ؊6 /°C in a H 2 atmosphere (oxygen partial pressure of 4 ؋ 10 ؊19 atm at 1000°C). La 0.8 Sr 0.2 Cr 0.9 Ti 0.1 O 3 perovskite with a linear thermal expansion in both oxidizing and reducing environments is a promising candidate material for an SOFC interconnect. However, there still remains an air-sintering problem to be solved in using this material as an SOFC interconnect.

“…However, much of the experimental work on these manganates has been motivated by their utility as a cathode material in solid oxide fuel cells (SOFCs), because they offer adequate electrical conductivity and reasonable thermal expansion match to yttria-stabilized zirconia and are stable in SOFC cathode operating environments. [1][2][3][4] The electronic transport and magnetic properties of some of these materials, particularly LaMnO 3 and La 1-x (Ca or Sr) x MnO 3 , have been investigated. [5][6][7][8] The transport properties of La 1-x Ca x MnO 3 are very sensitive to the variation of La/CaMnO 3 composition ratio and resultant change of 3d electron numbers, i.e., manganese valence, which greatly affects the electronic properties of these materials.…”

Section: Introductionmentioning

confidence: 99%

Alternating‐Current Electrical Properties of CaMnO₃ below the Néel Temperature

Jung

Sohn

Lee

et al. 2000

The alternating-current electrical properties of polycrystalline CaMnO 3 were investigated by alternating current compleximpedance analysis, and the dielectric properties were analyzed over the temperature and frequency ranges of 10 to 130 K and 20 Hz to 1 MHz, respectively. Direct-current conductivity and the Seebeck coefficient as a function of temperature also were analyzed. Below 120 K, a Debye-type dielectric relaxation peak was observed. Experimental results implied that the number of charge carriers, which were generated by Mn 3؉ , were not sufficient to stabilize small polarons, although it induced lattice distortion by the Jahn-Teller effect. Therefore, the thermal motion of Mn 3؉ between potential minimums produced by lattice distortion in the orthorhombic structure were believed to be the source of dielectric relaxation. The temperature dependence of conductivity of the grain interior ( gi ) below 120 K was believed to be due to variable rangehopping conduction, where gi Ϸ exp(؊T ؊1/4 ).