Defect characterization of slow-cooled and quenched samples of calcium-copper-titanate through positron annihilation spectroscopy

Fe3+-substitution effect on the thermal variation of J–E characteristics and DC resistivity of quadruple perovskite CaCu3Ti4O12

“…under investigation, D increases from 3.7 μm for x = 0.0 composition to 7.9 μm for x = 0.5 composition and then abruptly decreases to 3.4 μm for x = 0.7 composition [33] . The increase of D means that there is a decrease in the number of grainboundary barriers.…”

“…A careful structural analysis demonstrates that the x = 0.0-0.5 compositions are formed in the single phase with cubic perovskite crystal symmetry in the space group Im3. For the composition with x = 0.7, the aciculate but low intensity (~ 4.0 %) peak centered at 2θ = 25.6° is due to a trivial amount of anatase structure of well-crystallized TiO 2 [33] . The secondary phase is randomly distributed within the primary CaCu 3 Ti 4 O 12 matrix.…”

“…It is now feasible to elucidate the compositional variation of J max . The occupancy of metallic cations such as Ca 2+ , Cu 2+ , Ti 4+ and Fe 3+ among the crystallographic interstitial sites determined from Rietveld refinement of X-ray diffraction patterns revealed that with Fe-substitution the Cu 2+ -ion concentration at the A´ decreases from 3.0 for x = 0.0 composition to 1.53 for x = 0.7 composition [29,33] , as displayed in Table 2. This results in the curtailment of electric conduction through the square-planar site, and thus J max decreases rapidly for x = 0.0-0.3 compositions and then levels off for the compositions with x = 0.5 and 0.7, as shown in Table 1.…”

“…The percentage formation of these secondary phases is well below the theoretical percolation threshold (~16%) and experimental percolation threshold (~20%) values. This would ensure that electric behavior such as E s and J max would always be dominated by the CaCu 3 Ti 4 O 12 phase [33] . An effort has been undertaken to correl- ate the previous outcome of the PAL spectroscopy study [29] and present electric parameters as a function of composition (x).…”

“…A series of cubic perovskites, CaCu 3-x Ti 4-x Fe 2x O 12 with x = 0.0, 0.1, 0.3, 0.5 and 0.7, was prepared by the mixed oxide route. The complete details regarding the synthesis, crystallographic phase identification, and structural parameters including cationic distribution determination by employing Rietveld refinement of X-ray powder diffraction data and average grain size (D) estimation by analyzing scanning electron micrographs are given elsewhere [27,33] . The measurements of current (I) versus applied signal voltage (V) (V = 0-400 V) (I-V characteristics) were carried out with the help of an Aplab made high-voltage dc regulated power supply (model no.‫׃‬ 7332) at temperatures ranging from T = 300-673 K using the two probe pressure contact method and a horizontal electric furnace.…”