ICP-AES and MicroRaman corrosion behaviour investigation on Zn4Sb3 and Al, Ag doped phases in sodium chloride solution

The high thermoelectric performance of the b-phase Zn4Sb3 has drawn much attention for its application in the intermediate temperature range. In this work we explore the corrosion behaviour properties of pure Zn4Sb3 compound and after partial substitution of Zn with Al and Ag. In particular, Zn4Sb3, (Zn1xAlx)4Sb3 and (Zn1xAgx)4Sb3 (x = 0.01) compounds were synthesized using a muffle furnace and characterized in terms of crystal structure, morphology and phases composition (SEM-EDXS, XRD). All samples were placed in 0.1 M NaCl aerated solution at room temperature for 48 days. A study of the amount of cations released in solution was carried out using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) analysis. Analytical data reveal a higher value of zinc amount for doped samples. The microRaman spectroscopy analysis carried out on surface corrosion products revealed the presence of anhydrous and hydrate zinc hydroxy chlorides. No worsening on corrosion behaviour of Zn4Sb3 intermetallic compounds was observed after Al or Ag doping

Thermal expansion and high temperature structural features of the filled skutterudite Sm\u3b2(Fe\u3b1Ni1-\u3b1)4Sb12

A structural study was performed by high temperature x-ray diffraction on samples of the filled skutterudite Sm\u3b2(Fe\u3b1Ni1-\u3b1)4Sb12 between 303\ua0K and 773\ua0K, i.e. in the range including the highest values of the dimensionless figure of merit ZT for this system. Samples were prepared by direct reaction of the pure elements at 1223\ua0K, followed by an annealing treatment at 873\ua0K. Morphology and composition of the obtained alloys were checked by SEM-EDS; the coefficient of thermal expansion (CTE) was calculated from the refined values of the cell parameter, and its trend as a function of the Fe amount revealed a discontinuity in proximity of the composition separating p- and n-skutterudites. Since the reduction of thermal stresses is a fundamental requirement for the lengthening of the thermoelectric devices lifetime, this evidence suggests useful hints for the choice of the most proper skutterudite compositions to be used in p- and n-legs. The effect of increasing temperature on other structural parameters, such as the shape of the Sb4 rings, is considered too and discussed in terms of filling degree of the cell

Thermoelectric properties of Zn4Sb3 intermetallic compound doped with Aluminum and Silver

The beta-phase Zn4Sb3 has attracted much attention because of its high thermoelectric performance in the intermediate temperature range thanks to disorder in the Zn lattice site. In this work are presented structural, thermal, electric and thermoelectric characterization of Zn4Sb3 pure and Ag, Al doped, prepared by a simple synthesis. Structural and microstructural analyses reveal homogeneous one-phases having compositions in agreement with the nominal ones. After thermoelectric characterization, Ag doping results mostly effective in lowering the resistivity and Seebeck coefficient value, by introducing holes in the system. On the other hand, the Al substitution yields a very small decrease of the Seebeck coefficient but, at the same time, a significant decrease of the thermal conductivity mainly due to the depressed phonon contribution. The thermal conductivity behavior is the main responsible for the good thermoelectric performances of (Zn0.33Al0.01)(4)Sb-3, whose thermoelectric figure of merit reaches the encouraging value of 0.23 at 260 K

ICP-AES and microRaman corrosion behaviour investigation on Pb, Sb, Bi tellurides in sodium chloride solution

Tellurides are in years considered among the best intermetallic compounds for thermoelectric applications in the low-intermediate- temperature range. The corrosion behaviour of pure Pb, Sb and Bi tellurides is investigated in this work through a spectroscopic approach. The samples are synthesized using a muffle furnace and then placed in 0.1 M NaCl aerated solution at room temperature for 48 days. All samples are characterized, prior to and after immersion, in terms of crystal structure, morphology and phases composition (SEM-EDXS, XRD). A study of the ionic release, using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) analysis, is also carried out. Furthermore, a microRaman spectroscopy study is performed on surface corrosion products. The preliminary results reveal that PbTe and Bi2Te3 show the best corrosion resistances in the considered environment

Synthesis and characterisation of the compound CoSbS

In the search for new intermetallic materials with high thermoelectric performances, the Co\u2013Sb\u2013S ternary system has been explored and polycrystalline CoSbS samples have been prepared by a vapour phase technique starting from the pure elements. The crystal cell of CoSbS belongs to the Pbca space group and shows an orthorhombic structural arrangement with the following lattice parameters: a = 5.8341(2) A \ub0 ; b = 5.9477(2) A \ub0 , and c = 11.6540(4) A \ub0 . The structure belongs to the pyrite\u2013marcasite family, as Co forms tilted corner- and edge-sharing octahedra with three Sb and three S atoms. Scanning electronic microscopy (SEM), electron-probe microanalysis (EPMA) and X-ray powder diffraction were used to investigate the microstructure and to carry out the structural analysis; the crystal structure was refined by the Rietveld method using the DBWS-9807 program. The thermal stability of CoSbS was investigated referring to the ternary Co\u2013S\u2013Sb phase diagram and by differential thermal analysis (DTA) measurements. Thermoelectric power measurements at room temperature were also performed by a home-made instrument

Correlations between Structural and Electronic Properties in the Filled Skutterudite Smy(FexNi1-x)4Sb12

A structural study of the filled skutterudite Smy(FexNi1-x)4Sb12 was performed by means of X-ray powder diffraction and -Raman spectroscopy with the aim to unveil the correlations between structural and electronic properties of this material and to favor the improvement of its thermoelectric performance. Samples were prepared by direct reaction of the elements at 1223 K, followed by quenching and subsequent sintering at 873 K; microstructure and composition of the obtained products were determined by SEM-EDS. The position of the boundary separating regions that obey hole- and electron-based conduction mechanisms was found by X-ray diffraction at x 0.63 and y 0.30, confirmed by measurements of room-temperature Seebeck coefficient, and discussed on the basis of crystallographic data. The presence of a discontinuity is observed in several structural and spectroscopic parameters at the p/n crossover; it is interpreted as associated with the change in the conduction mechanism. The role of the rare earth filling fraction in driving the structural response of the material is investigated too. The advantage of using X-ray diffraction and -Raman spectroscopy as aids in the study of electronic properties of this material is highlighted, as well as the complementarity of the two techniques