Abstract
The DC electrical resistivity results of La4 −x Sr1 +x Cu5 −x Fe x O12 + δ (0 ≤x ≤ 1·0) showed that for S1 (x = 0) and S2 (x = 0·25) the temperature coefficient of resistivity (TCR), dρ/dT, is positive and slightly increases with increasing temperature in the range 20–270 K. This shows the metallic nature of S1 and S2. For the samples S3(x = 0·5) and S4 (x = 0·75), TCR slightly increases in the range 20–270 K, with change in sign from negative to positive at ∼ 80 K and ∼ 130 K, respectively. These results show the metal-insulator type transition in S3 and S4. For the sample S5 (x = 1·0), the TCR is negative and gradually increases in the range 20–270 K, which shows its semiconductor-like behaviour. The activation energy for S5 is found to be 0·21 × 10−2 eV. Furthermore, the DC resistivity results of S1–S5 in the range 350–660 K are in conformity with the low temperature results. The very weak temperature dependence of magnetic susceptibility results of S1–S3 show Pauli-paramagnetic behaviour in the range 77K–400 K, while S4 and S5 exhibit Pauli-paramagnetic behaviour in the range 77–850 K. Long-range antiferromagnetic interaction is observed in S5 (x = 1·0) belowT c ∼ 100 K. The room temperature EPR lineshapes gradually improve from metallic S1 (x = 0) to semiconductor-like S5(x = 1·0). Negativeg-shift is observed in the samples S2–S5 with increasing trend ing iso-values of 1·880 in S2 to 1·961 in S5. However, theg iso-value for S1 could not be observed due to very poor lineshape.
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Das, B.B., Michel, C. & Raveau, B. Characterization of La1 −x Sr1 +x Cu5 −x Fe x O12 + δ (0 ≤x ≤ 1·0) by dc electrical conductivity, magnetic susceptibility and EPR measurements(0 ≤x ≤ 1·0) by dc electrical conductivity, magnetic susceptibility and EPR measurements. Bull. Mater. Sci. 19, 1059–1066 (1996). https://doi.org/10.1007/BF02744638
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DOI: https://doi.org/10.1007/BF02744638