Q.M. Lu

Effects of double filling of La and Ce on thermoelectric properties of CemLanFe1.0Co3.0Sb12 compounds by spark plasma sintering

Double-filled skutterudite compounds CemLanFeCo3Sb12 with (m+n)=0.2–0.4 were synthesized by spark plasma sintering using powders of Co, Sb, Fe, and rare-earth Ce and La as starting materials, and the thermoelectric properties were studied in detail. The dominant phases of all the samples are the skutterudite with small amount of Sb as an impurity phase, and the amount of Sb decreases in double-filled compound. The lattice constant is enhanced linearly up to (m+n)=0.30 with increasing filling fraction and then unchanged. The Seebeck coefficient and thermal conductivity of double-filled compounds are generally higher than single-filled samples whatever the filling fraction is. Among all the samples, Ce0.1La0.2FeCo3Sb12 shows the highest Seebeck coefficient of 150μVK−1 at 773K and the lowest thermal conductivity of 1.81W∕mK at 673K, and the maximum ZT value reaches 0.60 at 773K due to its lower thermal conductivity.

Preparation and improved electrical performance of the Pr-doped CaMnO3−δ thermoelectric compound

The rare earth Pr-doped Ca1?xPrxMnO3?? (0???x???0.14) compound bulk samples are fabricated by citrate acid sol?gel combined with the ceramic preparation method. The effects of Pr doping on the structural and electrical transport properties of CaMnO3?? within the high-temperature region are investigated in detail. The results show that single orthorhombic compounds can be formed in the experimental doping region. The remarkably reduced electrical resistivity is observed for the doped samples with the minimum value 3.90?m??cm at 373?K for the x?=?0.14 sample; the absolute value of the Seebeck coefficient is decreased due to electron carrier concentration enhancement. The electrical properties of the doped samples are optimized compared with that of the parent sample, and the x?=?0.08 sample is found to have the largest power factor value of 0.334?mW?m?1?K?2 at 873?K. It is confirmed from the investigation that the electrical performance could be improved remarkably by rare earth Pr doping at a lower content.

Phase structure and magnetic properties of Mn3Ga2 alloy

In this paper, Mn3Ga2 alloys with high saturation magnetization and high Curie temperatures were prepared by levitation melting high pure Mn and Ga elements followed by annealing. The effect of annealing temperature on phase structure and magnetic properties was investigated by means of x-ray diffraction and a vibrating sample magnetometer. A single phase alloy Mn3Ga2, which has tetragonal P4/mmm structure, was obtained with an annealing temperature of 773 K and annealing time of 24 h. The hysteresis curve of its easy axis for this single phase alloy shows that the room temperature coercivity and saturation magnetization are 4.18 kOe and 50.81 emu/g, respectively. The thermomagnetic curves indicate that the Curie temperature is about 650 K and a phase transformation occurs above 823 K.

Recrystallization and magnetic hardening in Mn 1.8 Ga magnet by spark plasma sintering deformation

Theoretical calculations for L1<inf>0</inf>-MnGa compound indicate a high anisotropy constant, K<inf>u</inf> (26 Mergs/cm³) and a saturation magnetization, M<inf>s</inf> (116 emu/g), which predict a maximum energy product, (BH)<inf>max</inf>, of 28 MGOe.

Synthesis and thermoelectric properties of nano/micro-meter CoSb3-based bulks processed by in-situ spark plasma sintering

Nanostructure materials exhibit different properties from those of corresponding bulk substances, the decrease in the grain size of the material leads to a drastic increase in the density of grain boundaries, which brings out a significant reduction in thermal conductivity, kappa, and so improve the value of thermoelectric figure-of-merit, ZT. But the decreased grain size reduces the electrical conductivity and Seebeck coefficient at the same time. Based on the above reasons, a novel method of in-situ spark plasma sintering (SPS) is used to synthesize CoSb3-based Skutterudite compounds with nano/micro-meter grains by controlling the grain size of raw materials, and the thermoelectric properties are studied systematically. The results indicate that, the ratio of electrical conductivity and thermal conductivity is optimized, and a relative high Seebeck coefficient is obtained at nano/micro-meter scale. As a result, the dimensionless figure of merit ZT is greatly improved for CoSb3, and La0.3FeCo3Sb12, the highest value of ZT of 0.34 and 0.72 is obtained at 700 K for CoSb3 and La0.3FeCo3Sb12 Skutterudite compound, respectively

The thermoelectric properties of (Ce,La)/sub y/Fe/sub 1.0/Co/sub 3.0/Sb/sub 12/ compounds by solid state reaction and spark plasma sintering

Filled skutterudite compounds (Ce,La)/sub y/FeCo/sub 3/Sb/sub 12/ with y=0.1/spl sim/0.3 were synthesized by solid state reaction-spark plasma sintering (SPS) using powders of Co, Sb, Fe and rare earth Ce as starting materials, and the thermoelectric properties of the compounds were also studied. It is shown that there is a little Sb in filled skutterudite compounds (Ce,La)/sub y/FeCo/sub 3/Sb/sub 12/ with y=0.1/spl sim/0.3 at 900 K. The lattice constant and the Seebeck coefficient of the compounds increases with the filling fraction of the Ce and La, while the thermal conductivity and electrical conductivity is greatly reduced The compounds had a minimum value of thermal conductivity with y=0.3, indicating that it is the coupling rattling and the irregular distribution between the two filler ions of La and Ce that give rise to the mass change of atom and the additional phonon scattering produced by lattice aberration when the Sb voids in the skutterudite structure were filled by Ce and La. The compound of Ce/sub 0.1/La/sub 0.2/Fe/sub 1.0/Co/sub 3.0/Sb/sub 12/ with Co-rich had a maximum value of the dimensionless figure of merit ZT=0.46 at 773 K.