SEM images of La0.65+3vCa0.35−3vMn1−vO3 samples with v = 0.03−0.06. Note large grains and melted grain boundaries.
(Color online) (a) Semilog plots of ρ vs T for La0.65+3vCa0.35−3vMn1−vO3 (0 ≤ v ≤ 0.06) (solid lines and symbols) and for La1−xCaxMnO3 (dashed lines). (b) S vs T for the above samples. Inset in (a): semilog plots of ρ vs T -1 for La0.83Ca0.17Mn0.94O3 and for La0.83Ca0.17MnO3 where it is seen that at Tc the activation energy Δ for the ordered sample (x = 0.17) exhibits a sharp drop followed at much lower T by a monotonic decrease; for the disordered sample (v = 0.06) the monotonic decrease of Δ starts around Tc .
(Color online) Log-log plots of J vs E at various temperatures for La0.65+3vCa0.35−3vMn1−vO3, (a) v = 0.04, (b) v = 0.06, and (c) for La0.83Ca0.17MnO3 (v = 0). Symbols represent pulsed measurements and solid lines - d.c. measurements. Dotted lines represent extrapolations of the ohmic current densities. Note the large hysteresis in the d.c. plots. Insets in (a) and (b): J/Jo vs E for several temperatures. Inset in (c): J vs E at 40 K on the linear scale that emphasizes the big difference between the pulsed and the d.c. measurements.
The parameters Eo (a) and β (b) derived from the relation J/Jo = 2(E/Eo ) β , fitted to the data points obtained at various temperatures for the non-metallic samples of La0.65+3vCa0.35−3vMn1−vO3 (0.04 ≤ v ≤ 0.06).
Nominal composition of the La1−xCaxMn1−vO3 samples, cell constants, and some linear and nonlinear transport properties at low temperatures.
Article metrics loading...
Full text loading...