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A study investigated the high-temperature thermoelectric properties, (p, s and k) of A-site substituted compounds. The method can be successfully employed to get the highest ZT is obtained for the Yb substituted compound and reaches a value of 0.16 at 1000 K in air.

CaMnO3 is an electron-doped compound which belongs to the perovskite family. Despite its high Seebeck coefficient S value, the figure of merit at high temperature remains low due to its large resistivity ρ(ρ300 K=2 Ω cm). To optimize the performance of this material in terms of thermoelectric properties, several substitutions have been attempted on the Ca site to decrease the ρ. Structure and thermoelectric properties of polycrystalline samples Ca1-xAxMnO3 (A=Yb, Tb, Nd, and Ho) have been investigated. Although ρ strongly depends on the ionic radius A> and carrier concentration, we have shown that the thermal conductivity κ is mainly driven by the atomic weight of the A site and decreases with it. Therefore, it seems that the S, ρ, and κ could be controlled separately. For instance, the highest dimensionless ZT (=0.16) has been obtained at 1000 K in the air for Ca0.9Yb0.1MnO3. [ABSTRACT FROM AUTHOR]

TiS2 based layered sulfides have recently received increasing interest from the thermoelectric community. Due to its layered structure, the TiS2 compound with its enormous capacity for chemical substitution and intercalation offers different means to optimize the thermoelectric response through concomitant tuning of carrier concentration and decrease of the lattice thermal conductivity. In this review, we first discuss and summarize the crystal structures and physical/chemical properties of TiS2 based layered sulfides. Then, the approaches that successfully enhanced the thermoelectric performances in the TiS2 ceramic samples densified by Spark Plasma sintering are outlined, which include intercalation, non-stoichiometry, cationic substitution, and the block layer concept. [ABSTRACT FROM AUTHOR]

Well-aligned anatase and rutile TiO2 nanorods and nanotubes with a diameter of about 80–130 nm have successfully been fabricated via sol-gel template method. The prepared samples were characterized by using thermogravimetric (TG) and differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). The XRD results indicated that the TiO2 nanorods were crystallized in the anatase and rutile phases, after annealing at 400–800 °C for different periods of time from 0.2 to 10 h. [ABSTRACT FROM AUTHOR]

We have used Ni and Co K-edge conversion electron yield X-ray absorption fine Structure (CEY-XAFS) and conventional XAFS in transmission mode to investigate LiNi0.8Co0.15Al0.05O2, one of the promising cathode materials for Li-ion batteries. The former technique is surface-sensitive, having a probing depth of ~90 nm, while the latter is bulk-sensitive. X-ray absorption near edge structure analysis revealed that the bulk-averaged Ni valences for cycle-tested cells and aging-tested cells are lower than that for a fresh cell throughout charging. Further reduction of Ni atoms is observed at the surface of the cathode material particles, and the ranges of the Ni valence change upon charging are narrower than that for a fresh cell, indicating the presence of Ni atoms which are unaffected by charging. Extended X-ray absorption fine structure analysis revealed that the change in bond lengths [Ni-O, Ni-M (M = Ni,Co), Co-O, and Co-M] is consistent with the change in the Ni valence. These electronic and structural changes occur predominantly at the surface and are probably the main causes of capacity fading. [ABSTRACT FROM AUTHOR]

A silicide material with a good n-type thermoelectric property has been discovered. This silicide possesses a composition of Mn3-xCrxSi4Al2 (0 ≤ x ≤ 0.7) and hexagonal CrSi2 structure. The a- and c-cell parameters decrease with increasing the amount of Cr substitution. The absolute values of Seebeck coefficient and electrical resistivity increase by Cr substitution up to 573 K because of reduction of carrier density. The dimensionless thermoelectric figure of merit ZT reaches 0.21 at 773 K for a non Cr substituted sample at the Mn site and 0.30 at 573 K for a Cr substituted one with x = 0.3. Since oxide passive layer is formed around the surface, electrical resistivity measured at 873 K is constant for 2 days in air, which indicates good oxidation resistance in air of this material. The Mn3-xCrxSi4Al2 is a promising n-type material with a good oxidation resistance in the middle temperature range. A thermoelectric module consisting of 64 pairs of legs has been fabricated using MnSi1.7 and non Cr substituted Mn3Si4Al2 devices as p- and n-type legs, respectively. Output power reaches 9.4 W, which corresponds to 2.3 kW/m2 of power density against surface area of the substrate, for a heat source temperature of 873 K in air. [ABSTRACT FROM AUTHOR]

Examines the thermopower of porous yttrium oxide. Ways of generating the thermopower; Calculation of nondimensional thermoelectric figure of merit; Measurement of the thermal conductivity.