Sb-doped Bi₂Te₃ is known since the 1950s as the best thermoelectric material for near-room temperature operation. Improvements in material performance are expected from nanostructuring procedures. We present a straightforward and fast method to synthesize already nanostructured pellets that show an enhanced ZT due to a remarkably low thermal conductivity and unusually high Seebeck coefficient for a nominal composition optimized for arc-melting: Bi_0.35Sb_1.65Te₃. We provide a detailed structural analysis of the Bi_2−xSb_xTe₃ series (0 ≤ x ≤ 2) based on neutron powder diffraction as a function of composition and temperature that reveals the important role played by atomic vibrations. Arc-melting produces layered platelets with less than 50 nm-thick sheets. The low thermal conductivity is attributed to the phonon scattering at the grain boundaries of the nanosheets. This is a fast and cost-effective production method of highly efficient thermoelectric materials.

We studied ferromagnet/superconductor/ferromagnet trilayers based on ${\text{La}}_{0.7}{\text{Ca}}_{0.3}{\text{MnO}}_3$ manganite and ${\text{YBa}}_2{\text{Cu}}_3{\text{O}}_{7-\delta }$ (YBCO) high-$T_c$ cuprate with magnetoresistance and magnetization measurements. We find an inverse superconducting spin-switch behavior, where superconductivity is favored for parallel alignment of the magnetization in the ferromagnetic layers. We argue that this inverse superconducting spin switch originates from the transmission of spin-polarized carriers into the superconductor. In this picture, the thickness dependence of the magnetoresistance yields the spin-diffusion length in YBCO as 13 nm. A comparison of bilayers and trilayers allows ruling out the effect of the stray fields of the domain structure of the ferromagnet as the source of the inverse superconducting spin switch.

La-filled skutterudites La_xCo₄Sb₁₂ (x = 0.25 and 0.5) have been synthesized and sintered in one step under high-pressure conditions at 3.5 GPa in a piston-cylinder hydrostatic press. The structural properties of the reaction products were characterized by synchrotron X-ray powder diffraction, clearly showing an uneven filling factor of the skutterudite phases, confirmed by transmission electron microscopy. The non-homogeneous distribution of La filling atoms is adequate to produce a significant decrease in lattice thermal conductivity, mainly due to strain field scattering of high-energy phonons. Furthermore, the lanthanum filler primarily acts as an Einstein-like vibrational mode having a strong impact on the phonon scattering. Extra-low thermal conductivity values of 2.39 W m⁻¹ K⁻¹ and 1.30 W m⁻¹ K⁻¹ are measured for La_0.25Co₄Sb₁₂ and La_0.5Co₄Sb₁₂ nominal compositions at 780 K, respectively. Besides this, lanthanum atoms have contributed to increase the charge carrier concentration in the samples. In the case of La_0.25Co₄Sb₁₂, there is an enhancement of the power factor and an improvement of the thermoelectric properties.

SnSe has been recently reported as an attractive thermoelectric material, with an extraordinarily high, positive, Seebeck coefficient. Here, we describe the synthesis, structural, microscopic, and thermoelectric characterization of Sn_1–xSb_xSe intermetallic alloys prepared by a straightforward arc-melting technique. Sb-doped tin selenide was synthesized as strongly nanostructured polycrystalline pellets. Neutron diffraction studies reveal that Sb is placed at the Sn sublattice in the crystal structure, showing concentrations as high as 30%, and generates a significant number of Sn vacancies, while the increase of the interlayer distances favors the nanostructuration. The material is nanostructured both out-of-plane in nanometer-scale layers and in-plane by ∼5 nm undulations of these layers. This nanostructuring, along with an increased amount of Sn vacancies, accounts for a reduction of the thermal conductivity, which is highly desirable for thermoelectric materials. The phonon mean free path is estimated to be on the order of 2 nm from low temperature, thermal conductivity, and specific heat, in accordance with the nanostructuration observed by high-resolution transmission electron microscopy. The thermal conductivity of SnSe is characterized by three independent techniques to assure a room temperature value of Sn_0.8Sb_0.2Se of κ ∼ 0.6 W/m K. The freshly prepared Sb-doped compounds exhibit an abrupt change in the type of charge carriers, leading to large, negative Seebeck coefficients, although the arc-melt synthesized pellets remain too resistive for thermoelectric applications. Cold-pressed pellets evolve to be p-type at room temperature, but reproducibly turn n-type around 500 K, with increased electrical conductivity and maximum observed figure of merit, ZT ∼ 0.3 at 908 K.

Low-cost n-type Mischmetal-filled CoSb₃ skutterudites with elemental filling-fraction separation, prepared at high pressure, exhibit markedly low lattice thermal conductivity.