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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: 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]