Danmin Liu

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.

Effect of annealing on the structure and magnetic properties of Mn1.1Fe0.9P0.8Ge0.2 compound

Effect of homogenization of the chemical composition and crystal structure on the magnetocaloric effects have been studied for bulk Mn1.1Fe0.9P0.8Ge0.2 alloy prepared by mechanical alloying and subsequent spark plasma sintering method. After optimal homogenization treatment, the ferromagnetic impurity, Ge6Fe3Mn4 phase was completely eliminated from the alloy; furthermore, the crystal lattice constant of the MnFePGe main phase, which possesses a hexagonal Fe2P-type structure, varies obviously compared with that of the sintered sample. As a result, the Curie temperature, TC, of the alloy increases from 253 to 267.5 K and the maximum magnetic entropy change, |ΔSm|, also increases from 36.36 to 44.35 J/kg K under 3 T magnetic field. Furthermore, the thermal hysteresis of M-T curves around TC upon heating and cooling, a signature of a first-order magnetic phase transition, reduces from 15 K for as-sintered sample to 9 K for annealed sample.

Crystal structure and magnetic transition of MnFePGe compound prepared by spark plasma sintering

The crystal structure and magnetic transition were studied for the bulk Mn1.1Fe0.9P0.8Ge0.2 compound prepared by a simple blending and subsequent spark plasma sintering route. X-ray diffraction analysis and refinement show that the compound crystallizes in the hexagonal Fe2P-type structure, in which the Mn atoms occupy all the 3g sites and some 3f sites, the Fe atoms occupy the rest of the 3f sites, and P and the Ge atoms randomly occupy the 2c and 1b sites. Magnetic measurement indicates that the Curie temperature TC is at 253K and the thermal hysteresis of M-T curves at TC upon heating and cooling, a signature of a first-order magnetic phase transition, is about 15K. The maximum magnetic entropy change of the compound reaches as high as 49.2J∕kgK in a field change from 0to5T at 253K, while the adiabatic temperature change of the compound reaches only 1.2K in a field change from 0to1.5T at the same temperature.

Epitaxial growth of biaxially oriented YBCO films on silver

YBCO films were deposited on (100), (110) and (111) oriented silver single crystals and { 100} 100, { 110} 211 and { 012} 100 biaxially textured Ag substrates by pulsed laser deposition. It is shown that the (100) and (110) orientated single crystals and the { 110} biaxially textured Ag tape are all suitable for the deposition of YBCO thin films with c-axis in-plane alignment. The Jc of YBCO film deposited on { 110} 211 biaxially textured Ag foil is 7×105A cm-2 at 77 K, 0 T. A scheme for the regular growth of YBCO on silver was put forward.

A newly designed ultrasonic spray pyrolysis device to fabricate YBCO tapes

Abstract A newly designed ultrasonic spray pyrolysis device has been manufactured to fabricate YBCO tapes. The apparatus is primarily composed of four zones: the ultrasonic generator, the atomization chamber, the pyrolysis chamber and the rotating equipment. Every part of them is designed and fabricated by us. The whole system costs far less than the ready-made equipment facility in which there is always a vacuum apparatus. This apparatus with processing parameters accurately controlled can fabricate short and long YBCO tapes. In this paper, we mainly focused on how to design and manufacture four parts of the ultrasonic spray pyrolysis. We have deposited c -axis aligned short YBCO tapes on biaxially textured Ag {1 1 0}〈1 1 0〉 substrates with J c =10 3 A/cm 2 using this method with our device. The method is very promising in terms of its precise control of metal compositions, high deposition rate and low cost non-vacuum approach. Improvements of this technique are being carried out to fabricate long YBCO tapes.

Preparation and formation mechanism of cube textured Ag substrate for coated high-Tc superconductor

Abstract A strong cube, {100}〈100〉, textured silver tape for coated high- T c superconductor was obtained. The hot-rolling textures and annealed textures of silver were studied systematically. Cube texture can be obtained by hot-rolling. In the process of rolling, twin formation must be avoided in order to increase the strength of the {211}〈111〉orientation. The crystals in {211}〈111〉orientation transforms into cube orientation by dynamic recrystallization and subsequent annealing.

Fabrication of YBCO tapes on Ag substrates by the ultrasonic spray pyrolysis method

15 cm long YBCO superconducting tapes with Jc of 104 A cm−2 were fabricated by the ultrasonic spray pyrolysis method. Predeposition for 15 min at 700 °C can effectively prevent the Ag substrate from vaporizing and diffusing into YBCO films, and improve the coarse surface of Ag, and the surface morphology and connectivity of YBCO films, and therefore increase the superconducting properties. Holding the temperature at 900 °C for 30 min after deposition improves the texture and connectivity of YBCO films.

A study on textured silver tapes used as substrates for YBCO high temperature superconductors

Abstract A single-component, {110}〈211〉, biaxially textured silver tape was obtained by cold-rolling and annealing. The cold-rolling textures and recrystallization textures of silver were studied systematically. It is shown that a sharp biaxial {110} texture can be obtained by using higher total rolling reduction, lower reduction per pass and higher annealing temperature. In-plane aligned YBCO film was deposited directly by pulsed laser deposition (PLD) on a textured silver foil having {110}〈211〉 orientation. The critical current density J c value of 5×10 5 A/cm 2 was obtained at 77 K, 0 T.

Advances in Mo-RE2O3 thermionic cathode materials

Abstract This paper presents recent advances in Mo–RE2O3(La2O3, Y2O3, Sc2O3) heated cathode materials. It is shown that Mo–La2O3–X (X=Y2O3, Sc2O3, Y2O3, +Sc2O3) have better elongation than Mo–La2O3. At operating temperatures of 1623–1673 K, the average saturation current of the Mo–La2O3 cathode is 118 mA, the maximum current reaching 174 mA; and the corresponding average current density is 367 mA/cm2, and the average emission efficiency is 11.8 mA/w. The lifetime is more than 2000 h when the stable emission current is 75–80 mA. These results show that the Mo–La2O3 cathode is closer to practical application.

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.