High Temperature Transport Properties of Nd_xCo₄Sb₁₂ Skutterudite Compounds

We report here on the transport properties at high temperature of partially Nd filled Co4Sb12 skutterudites. The NdxCo4Sb12 (0 ≤ x ≤ 0.05) compounds were prepared by a powder metallurgy technique. The electrical resistivity, thermopower, Hall coefficient, and thermal conductivity have been measured between 300 and 800 K. Influence on the thermoelectric performance of the introduction of Nd in the skutterudite cell is discussed. Some complementary results on NdxCo4-yNiySb12 are also introduced

Beneficial effect of Ni substitution on the thermoelectric properties in Ca_yCo_4-xNi_xSb₁₂ skutterudites

We have investigated the influence of nickel doping in a series of n-type CoSb3 skutterudite materials partially filled with Ca. The electrical resistivity, thermopower, and thermal conductivity have been measured in the 300–800 K temperature range on CayCo4-xNixSb12 compounds prepared by a powder metallurgy route. The chemical composition and structure have been analyzed by electron probe microanalyses and X-ray diffraction, respectively. It was found that the presence of nickel substantially decreases the electrical resistivity without any detrimental effect on the thermopower, resulting in an improvement of the power factor. The dimensionless thermoelectric figure ZT increases with increasing temperature and reaches a maximum value of 1 at 800 K

Specifické magnetické a transportní vlastnosti CuFeS2: Defekty hrají klíčovou roli

Our study targets some of the long-standing questions concerning the somewhat mysterious properties of chalcopyrite CuFeS2. We show that defect chemistry in connection with charge transfer within the structure is responsible for the unusual electronic and magnetic properties of CuFeS2. Specifically, our model addresses weak ferromagnetism and the high mobility of carriers on the background of a rigid antiferromagnetic structure. We show that defect structure can, counterintuitively, boost the mobility of free carriers due to defect-modified charge transfer. Further, the defect-modified charge transfer induces the weak ferromagnetism both in the Cu- and Fe-sublattice. This new view opens up space for further investigations and applications of charge transfer compounds.Tato studie si klade za úkol vysvětlit dlouho kladené otázky týkající se poněkud záhadných vlastností chalkopyritu CuFeS2. Ukazuje se, že za neobvyklé magnetické a elektronické vlastnosti tohoto materiálu jsou zodpovědné přítomné bodové defekty ve spojení s ´mechanismem přenosu náboje (CT) v této struktuře. Vypracovaný model osvětluje vznik slabého ferromagnetismu a vysoké pohyblivosti volných nositelů náboje na pozadí rigidní antiferomagnetické struktury. Defekty modifikovaný CT-přenos indukuje slabý feromagnetismus jak v Cu- tak i Fe-podmřížce krystalové struktury CuFeS2. Prezentovaný nový pohled otvírá prostor pro další zkoumání a využití CT-sloučenin

Thermoelectric Properties of Nd_xCo_4-yNi_ySb₁₂ Skutterudite Compounds

In an effort to further understand the influence of Nd on the thermoelectric properties of the binary compound CoSb3 and try to optimize them through doping, we prepared and investigated NdxCo4-yNiySb12 compounds. The samples have been prepared by a conventional metallurgical route. Structural analysis have been carried out by X-ray diffraction. The chemical composition and micro-homogeneity have been checked by electron probe microanalysis. Measurements of the electrical resistivity, thermoelectric power, thermal conductivity and Hall coefficient have been performed. The influence of both Nd and Ni on the thermoelectric properties of the binary parent CoSb3 is presented and discussed. Nd plays the role of a dopant (n-type) and the presence of Ni contributes to decrease significantly the electrical resistivity

Coexistence of a charge density wave and superconductivity in the cluster compound K2Mo15Se19

International audienceThe competition between charge density wave (CDW) and superconductivity is a central theme in condensed-matter physics with ramifications to correlated electron systems and high-temperature superconductivity. While the emergence of superconductivity is often observed upon suppressing the CDW transition by tuning the chemical composition or the external pressure, their coexistence has been reported in only a handful of materials, with the cuprates being the most prominent example. Here, we demonstrate that both cooperative electronic phenomena coexist in the cluster compound K2Mo15Se19 . The CDW transition sets in at T-CDW = 114 K, accompanied by a commensurate periodic modulation of the crystal lattice along the c axis evidenced by electron diffraction. Bulk type-II superconductivity develops upon further cooling below T-c = 2.8 K. The presence of similar signatures of CDW ordering in other A(2)Mo(15)Se(19) compounds shows that this electronic instability may be ubiquitous in these compounds, providing a novel family where the interplay between CDW and superconductivity may be systematically investigated