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Structure and transport properties have been studied for a series of La0.75−xRExCa0.25MnO3 manganites with heavy rare earth ions of Gd, Dy, Ho substituting La with x = 0, 0.10, 0.25, 0.50, and 0.75. Polycrystalline samples were prepared by the carbonate precipitation route. The oxygen content was determined by the iodometric titration. The X-ray investigations carried out by the powder method show that the unit cell volume gradually decreases and orthorhombic distortion of the lattice increases with rising RE content. Below the room temperature the electrical resistivity is of the semiconducting type for all the samples studied. Electrical resistivity vs. temperature dependences were analyzed within different models: simple thermal activation, Mott's variable range hopping, adiabatic, nonadiabatic, and bipolaron. The Curie temperatures of Gd, Dy, and Ho substituted manganites determined from magnetization measurements show that at 280 K all the samples are in the paramagnetic phase. The increasing RE fraction reduces magnetization at 4 K as compared to La0.75Ca0.25MnO3.

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1 Abstract. The Sr 3 LaTa 3 O 12 layered powdered perovskitelike compounds were obtained by heat treatment of coprecipitated hydroxy-carbonates. Photoluminescent (PL) properties of the Sr 3 LaTa 3 O 12 were investigated at the first time. Strongly overlapped components peaked at 535, 585 and 630 nm compos emission spectra of the materials under study. The luminescent data were analyzed and preliminary assumptions about origin of given spectra have been made.

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Aus Mischfällungen der Hydroxide werden die Granate (I) erhalten.