Calorimetric, thermal expansion, resistivity, and magnetization measurements in La 2/3 (Ca 1Ϫx Sr x) 1/3 MnO 3 samples evidence the existence of a critical tolerance factor t that determines the relevance of lattice effects in mixed-valence manganites. Samples with xϽ0.15 ͑i.e., with tϽ0.92) exhibit a first-order magnetic transition at the Curie temperature T C as well as anomalous volume and magnetic entropy changes, high volume sensitivity to magnetic fields and high magnetoresistance at T C ; whereas those with tϾ0.92 do not. Samples of the former group show orthorhombic structures, whereas the other are rhombohedral. Taking into account that a rhombohedral symmetry forbids a static long-range-cooperative Jahn-Teller distortion, these results are taken as a probe of the strong reduction of lattice effects beyond this critical value of the tolerance factor. A new phase boundary in the phase diagram of manganese perovskites, that separates not only crystallographic phases, but also samples in which lattice effects must be taken into account, is proposed.

A need exists for low-cost coated-conductor fabrication methods for applications in magnet and electric-power technologies. We demonstrate high-critical current density (Jc) YBa2Cu3O7−δ (YBCO) films grown on Nb-doped SrTiO3 (Nb:STO) buffered Ni(100) tapes. All buffer and superconductor layers are deposited using solution chemistry. A 50 nm thick Nb:STO seed layer on Ni(100) acts as a template for the growth of subsequent thicker layers of Nb:STO. Nb doping improves the electrical conductivity and oxygen diffusion barrier properties of STO. YBCO grows heteroepitaxially directly on this buffer layer, resulting in a transport Jc(77 K)=1.3 MA/cm2.

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