Perovskite-type CaMn(1-x)Nb(x)O(3+/-delta) (x = 0.02, 0.05, and 0.08) compounds were synthesized by applying both a "chimie douce" (SC) synthesis and a classical solid state reaction (SSR) method. The crystallographic parameters of the resulting phases were determined from X-ray, electron, and neutron diffraction data. The manganese oxidations states (Mn(4+)/Mn(3+)) were investigated by X-ray photoemission spectroscopy. The orthorhombic CaMn(1-x)Nb(x)O(3+/-delta) (x = 0.02, 0.05, and 0.08) phases were studied in terms of their high-temperature thermoelectric properties (Seebeck coefficient, electrical resistivity, and thermal conductivity). Differences in electrical transport and thermal properties can be correlated with different microstructures obtained by the two synthesis methods. In the high-temperature range, the electron-doped manganate phases exhibit large absolute Seebeck coefficient and low electrical resistivity values, resulting in a high power factor, PF (e.g., for x = 0.05, S(1000K) = -180 microV K(-1), rho(1000K) = 16.8 mohms cm, and PF > 1.90 x 10(-4) W m(-1) K(-2) for 450 K < T < 1070 K). Furthermore, lower thermal conductivity values are achieved for the SC-derived phases (kappa < 1 W m(-1) K(-1)) compared to the SSR compounds. High power factors combined with low thermal conductivity (leading to ZT values > 0.3) make these phases the best perovskitic candidates as n-type polycrystalline thermoelectric materials operating in air at high temperatures.

Scheelite related compounds with general formula M n (XO 4 ) m are the subject of hefty interest owing to their optical properties, stability and relatively simple preparation. Eu 3+ -containing scheelites are considered as redemitting phosphors and the main factors affecting their luminescence are thought to be chemical composition and particle size while the influence of their structure is generally ignored. Here we report eight compounds from the Na x Eu (2Àx)/3 MoO 4 series prepared by conventional solid-state reaction and present a detailed analysis of their crystal structures. Six of them have modulated structures, a common feature of SRCs, in which dopant Eu 3+ ions are orderly distributed. Moreover, different amounts of Eu 3+ dimers are detected in the modulated structures, characterized by weak satellite reflections appearing in the lower angle part of the XRD patterns. These reflections are indexed and incorporated into Rietveld's refinement using superspace (3 + 1)-dimension symmetry. The remarkable feature of the compounds is that the characteristic luminescence parameters, overall (Q Eu L ) and intrinsic (Q Eu Eu ) quantum yields, Eu( 5 D 0 ) lifetimes, and sensitization efficiencies (h sens ), correlate with the number of Eu 3+ aggregates, but not directly with the composition x of the materials. This provides an efficient tool for understanding and controlling the luminescence properties of scheelite related compounds.

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