CHARACTERIZATION OF LA1-XSR1-XFEXO12+DELTA R-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1-CENTER-DOT-0) BY DC ELECTRICAL-CONDUCTIVITY, MAGNETIC-SUSCEPTIBILITY AND EPR MEASUREMENTS(XCU5)

The DC electrical resistivity results of La4 - xSr1 + xCu5 - xFexO12 b (0 less than or equal to x less than or equal to 1.0) showed that f or S1 (x = 0) and S2 (x = 0.25) the temperature coefficient of resisti vity (TCR), d rho/dT, is positive and slightly increases with increasi ng temperature in the range 20-270 K. This shows the metallic nature o f S1 and S2. For the samples S3(x = 0.5) and S4(x = 0.75), TCR slightl y increases in the range 20-270 K, with change in sign from negative t o positive at similar to 80 K and similar to 130 K, respectively. Thes e results show the metal-insulator type transition in S3 and S4. For t he 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 x 10(-2) eV. Furthermore , the DC resistivity results of S1-S5 in the range 350-660 K are in co nformity with the low temperature results. The very weak temperature d ependence of magnetic susceptibility results of S1-S3 show Pauli-param agnetic behaviour in the range 77 K-400 K, while S4 and S5 exhibit Pau li-paramagnetic behaviour in the range 77-850 K. Long-range antiferrom agnetic interaction is observed in S5 (x = 1.0) below T-c similar to 1 00 K. The mom temperature EPR lineshapes gradually improve From metall ic S1(x = 0) to semiconductor-like S5(x = 1.0). Negative g-shift is ob served in the samples S2-S5 with increasing trend in g(iso)-values of 1.880 in S2 to 1.961 in S5. However, the g(iso)-value for S1 could pot be observed due to very poor lineshape.