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Several studies are conducted to explain the structural, magnetic, as well as the transport properties exhibited by the [Bi.sub.0.6][Ca.sub.0.4]Mn[O.sub.3] compounds. The various impacts caused by the progressive substitution of the Bi ion by the La ion on these properties are also analyzed.

Highlights: [•] Multiple temperature-induced magnetization reversals were observed in x =0.1. [•] Coexistence of normal and inverse magnetocaloric effects was observed. [•] A reasonable model was proposed to explain the magnetization reversals. [Copyright &y& Elsevier]

Abstract: We have synthesized a series of layered cobaltite Bi2Sr2−x Ca x Co2O y (0≤x≤0.3). Reduced resistivity was observed with x≤0.2 due to the possible chemical pressure induced charge transfer between the Bi2Sr2O4 layer and CoO2 layer. Enhanced thermoelectric power S was also observed in the Ca-doped samples with the largest S as for x=0.2. The variation of S(T) could reflect the change of electronic correlation or the modification of local density of states and band structure near the Fermi energy. In addition, magnetic measurements show that the samples with x=0.0 exhibit abnormal and abrupt changes, revealing a possible thermally excited spin-state transition. It is found that the thermoelectric performance is obviously enhanced by the low Ca-doping. [Copyright &y& Elsevier]

Abstract: Single-phase Bi0.85La0.15FeO3 ceramics were synthesized under various magnetic fields (H a=0T, 3T, 5T). Substantially reduced leakage current and hence modified ferroelectric (FE) properties were obtained with magnetic field annealing (MA). The largest magnetization and lowest leakage current with large FE polarization (P r∼33μC/cm2) were found in the sample annealed with H a=3T. Great changes were also observed in the Raman spectra. All the observed features originate mainly from the different FE domain wall structures induced by MA. These results demonstrate that MA is an effective way to tune the multiferroic and magnetoelectric properties in BiFeO3-based materials. [Copyright &y& Elsevier]

Abstract: Layered misfit cobaltite Bi2Ca2.4Co2O y has been synthesized by a sol–gel method. This compound exhibits large thermoelectric (TE) power (S 300K∼170μVK−1), low resistivity (ρ 300K∼42mΩcm) and relatively small thermal conductivity (κ 300K∼2.8WK−1 m−1) at room temperature. Furthermore, the resistivity of this compound displays a metallic behavior above T ⁎∼150K with a semiconducting behavior below this temperature. This abnormal behavior in resistivity is analogous to those observed in Sr and Ba based misfit cobaltites. The observed features of the TE have been discussed based on the narrow band model. [Copyright &y& Elsevier]

Abstract: Mn-substituted Bi0.8Ca0.2FeO3 ceramics Bi0.8Ca0.2Fe1−x Mn x O3 (0≤ x ≤0.5) were synthesized by a solid-state reaction method. Powder X-ray diffraction investigations performed at room temperature show that the crystal structure is rhombohedral for x ≤0.1 and orthorhombic for 0.2≤ x ≤0.5. Compared to the undoped Bi0.8Ca0.2FeO3 compound, enhanced magnetization and electric polarization were observed in the samples with x ≤0.1. A further increase in the magnetization with increasing x took place in the samples with 0.2≤ x ≤0.5. All the Mn-substituted samples studied are basically antiferromagnetic accompanied by the appearance of weak ferromagnetism, which is similar to the BiFeO3 compound. The conductivity of the samples with x ≥0.3, measured between 140 and 380K, is of the semiconducting type. [Copyright &y& Elsevier]

Abstract: Y Fe0.5Cr0.5O3 ceramics have been synthesized by a conventional solid-state reaction. Powder X-ray diffraction shows that this compound possesses an orthorhombic structure with Pnma space group. It exhibits a high magnetic transition temperature at around 250 K with weak ferromagnetic behavior below this temperature. A dielectric relaxation following the Arrhenius law found in the Y Fe0.5Cr0.5O3 compound can be attributed to the charge carrier hopping conduction. [Copyright &y& Elsevier]

Abstract: Detailed magnetic properties of polycrystalline Bi0.3Ca0.7Mn0.75Cr0.25O3 are investigated. It is observed that this compound exhibits negative magnetization below the compensation temperature (T comp) when magnetization–temperature (M–T) curves are measured in a field-cooled mode with low applied fields (H <1030Oe). Furthermore, the compound shows a canted-antiferromagnetic transition at 120K and a peak with positive sign at 98K. Below 98K, M decreases with decreasing temperature, passes through a zero value (M =0) around T comp =78.5K, and continues to decrease steeply until 5K. The maximum absolute value of M below T comp was about 15 times as large as that above T comp. Considering the fact that the observed behavior is similar to that in GdCrO3, the phenomenon of the magnetization reversal in the Cr-doped manganite Bi0.3Ca0.7Mn0.75Cr0.25O3 is suggested to originate from the antiparallel coupling of the Cr3+ moments and the canted Mn3+/4+ moments. [Copyright &y& Elsevier]