We report on the thermoelectric properties of CuxTiS2 bulk compounds. Copper cations have been intercalated into the layered chalcogenide TiS2 by spark plasma sintering. X-ray diffraction analysis coupled to transmission electron microscopy shows that the lattice constant c expands linearly as the Cu content x increases. The Cu-intercalation into TiS2 leads to substantial decrease in both electrical resistivity and lattice thermal conductivity as compared to those of pristine TiS2. The figure of merit, ZT, is increased up to 0.45 at 800 K for x = 0.02. The power factor, PF, reaches 1.7 mW/mK2 in TiS2 at 325 K.

The spinel FeV2O4 is known to exhibit peculiar physical properties, which is generally ascribed to the unusual presence of two cations showing a pronounced interplay between spin, orbital and lattice degrees of freedom (Fe2+ and V3+ on the tetrahedral and octahedral sites, respectively). The present work reports on an experimental re-investigation of this material based on a broad combination of techniques, including x-ray diffraction, energy dispersive and M\"ossbauer spectroscopies, as well as magnetization, heat capacity, dielectric and polarization measurements. Special attention was firstly paid to establish the exact cationic composition of the investigated samples, which was found to be Fe1.18V1.82O4. All the physical properties were found to point out a complex ordering process with a structural transition at TS = 138 K, followed by two successive magnetostructural transitions at TN1 = 111 K and TN2 = 56 K. This latter transition marking the appearance of electric polarization, magnetization data were analysed in details to discuss the nature of the magnetic state at T< TN2. An overall interpretation of the sequence of transitions was proposed, taking into account two spin couplings, as well as the Jahn-Teller effects and the mechanism of spin-orbit stabilization. Finally, the origin of ferroelectricity in Fe1.18V1.82O4 is discussed on the basis of recent models.Comment: 26 pages, 9 figures,59 references.Accepted by Physical Review