La. Tikhonova et al., Doping effects on the physicochemical and electrochemical properties of lanthanum manganite, INORG MATER, 36(10), 2000, pp. 1036-1042
The structural, thermal, electrical, and electrochemical properties of La0.
7Ca0.3Mn1-x(Co,Ni)(x)O-3 and La0.6Sr0.4Mn1-x(Co,Ni)(x)O-3 (x = 0, 0.02, 0.0
5, 0.1) electrode materials were studied. Doping of the cubic perovskites w
ith Co or Ni increases the fraction of Mn4+ ions, up to 49% in La0.7Ca0.3Mn
0.9Co0.1O3 and 57% in La0.6Sr0.4Mn0.95Co0.05O3. The 300-K conductivity of L
a0.7Ca0.3Mn1-xNixO3 passes through a maximum at x = 0.05, while that of La0
.6Sr0.4Mn1-xCoxO3 decreases steadily with increasing x. In the range 300-11
00 K, the conductivity of the Ca-containing manganites exhibits semiconduct
ing behavior, whereas that of the Sr-containing materials shows metallic be
havior. No phase transformations were detected in this temperature range. I
n the four systems, the thermal-expansion coefficients are virtually indepe
ndent of x. In both undoped and doped electrode materials, the resistance p
arameter pld of electrode layers on solid-electrolyte substrates shows semi
conducting behavior at temperatures from 300 to 1100 K and oxygen partial p
ressures from 10(2) to 10(5) Pa. With increasing oxygen partial pressure or
electrode-layer thickness (d = 15-100 mg/cm(2)), rho /d decreases. The opt
imal electrode-layer thickness is found to be about 50 mg/cm(2). The introd
uction of Co or Ni into the electrode materials decreases the polarization
resistance of the electrode layer in gas/electrode/electrolyte systems. Com
positions ensuring the lowest polarization resistance were found.