Category: Day5(Aug.31)

Thermoelectric properties of Fe and V co-substituted higher manganese silicides (A5-K31-001)

Professor Yuzuru MIYAZAKI from the Tohoku university, Japan and his colleagues have been studied the influence of the transition metal V, Cr, Fe, Co for the 3d serie, Nb, Mo, Ru and Rh for the 4d and Ta, W, Re and Ir for the 5d serie as Mn substitution in the Higher Manganese Silicide (Mn(1-x)Mx)4Si7 material. The DFT calculation allowed to determine a theoretical electrical conductivities and Seebeck to calculating the power factor and the anisotropic properties. The limitation of the substitution were also exposed for these elements which showed a very good substitution in the case of the Re elements in the structure.

An increasing of the ZT from 0.2 to 0.4 was obtained with the Cr dopant. Iron substitution allows to modify the p or n type semiconducting nature of the material, HMS become n type when x is larger than 0.27.
Ru dopant generates small separated domains rich and poor in Ru which decrease the power factor.

Vanadium has been tested for x below 0.06 and has generated a structural modification which are visible by XRD technique. It’s impact the striation (presence of Mn1Si1 out of c axis) of the HMS phase. This striation vanishes after SPS processing. It generates a high variation of the electrical conductivity without any reduction of the Seebeck coefficient. In the case of Vanadium, a very good ZT value of 0.59 was obtained. Iron and vanadium co-doping has also been synthetized and showed a better thermoelectric properties with a maximum ZT value of 0.67. The last part of the talk was devoted to the strangest thermal HMS expansion due to striation and a variation of Mn/Si ratio. As conclusion, professor MIYAZAKI predicts the possibility to increase drastically the ZT coefficient of HMS thank the co doping and a good nanostructuration.

Partially substitution of heavy elements in n-type higher manganese silicide (A5-O31-002)

The speaker Swapnil GHODKE and his colleagues have been tested the multidoping Re, W, Ta and Fe in the HMS structure in the aim to reduce the rare metal Re need quantity as dopant. They studied various W/Re/Ta ratio. All of the compositions are stables in temperature excepted for W which is limited to a temperature below 1000K. The thermal conductivity was measured thank AC calorimetry and showed a very low value of 1.2W/m/K. These results could be give a solution to reduce the Re using element for HMS doping with an increase in of the thermoelectric properties.

Performance, stability and module integration of Higher Manganese Silicides materials solidified by Ribbon Growth on substrate RGS process (A5-O31-003).

The Speaker Pierre-Yves PICHON and his colleagues have been studied the evolution of the Mn(Si99.55Al0.45)1.73 properties in temperature and cycling. The speaker showed a new planar geometry for TE device which has been tested with a thermal gradient applied thank a thermal radiation. The electrical properties were measured for a lot of cycles in temperature. A variation of electrical resistivity was measured in temperature but still constant in the time while the Seebeck coefficient was not clearly modified. The microstructural analysis showed cracks in the HMS material. The Mn/Si ratio of HMS phase evolves with the cycling time in the using temperature condition and leads to a segregation of Mn1Si1 phase at grains boundaries. As the result, the quantity of cracks increases with the cycling time in the Al doped HMS material.

Low Temperature Plasmas in Nanotechnology Applications

Meyya Meyyappan of NASA Ames Research Center, USA, gave a keynote lecture in the oral session of Symposium C-5 in the morning session on August 31. He presented an overview of his activities on the use of low temperature plasmas in the growth of nanomaterials and application development. First, he introduced the atmospheric pressure plasma jet developed as an alternative to inkjet printing to deposit nanomaterials on paper, plastic, metal foils and textiles to enable flexible, printable electronics. Examples of printing copper, silver, carbon nanotubes, zinc oxide and others on paper, cotton and plastics were discussed. Second, he emphasized that low temperature plasmas have been effective to grow carbon nanofibers and graphene of a variety of applications, and used them as nanoelectrodes arrays for biosensing applications. Finally, he showed vertical graphene or carbon nanowalls synthesized by PECVD, which have interesting properties.

Advanced Plasma Technologies for ‘CubeSat’ Nano-Satellites

Christine Charles of Australian National University, Australia, gave a keynote lecture in the oral session of Symposium C-5 in the afternoon session on August 31. She presented that ‘CubeSat’ nano-satellites (based on the 10 cm by 10 cm by 10 cm modular unit) provided low-cost access to space and open doors to unprecedented unique projects accessible to universities and small companies. The process was facilitated by ongoing miniaturization at lower cost of electronics systems and components. ‘CubeSat’ was launched into space to study the ionosphere and the lower thermosphere, using a range of plasma sensors. In the miniaturized Pocket Rocket thruster, a radio frequency plasma is employed to heat the gas via charge exchange collisions and ambipolar flow to create a form of electrothermal thruster which has its heating mechanism in the center of the flowing propellant.

Poster Session

Poster session of Symposium C-5 was held in the evening on August 31. There were 23 poster presentations, and active discussion was held by the many participants.

Poster presentation scene of Symposium C-5.

The program started with an excellent keynote presentation by Mark S. Golden from the Van der Waals-Zeeman Institiute in Amsterdam, “Topological insulators and superconductors”. After a good introductory overview on topologically non-trivial states of matter, Mark presented their efforts in microfabricated structures of topological materials. Topological uperconductivity including interesting novel in-gap states were observed in superconductor/topological semi-metal Josephson junctions and the bulk properties of topological superconductors were addressed.

The next talk by Alex Drozdov from the Max-Planck-Institute of Chemistry in Mainz covered one of the most exciting recent developments in the field of superconductivity in his talk “High temperature superconductivity in hydrides at high pressures” . Long believed to suffer from an upper boundary in the maximal superconducting transition temperature around 30K, phonon-mediated conventional BCS-superconductivity recently entered the stage of high temperature superconductivity. In metallic sulfur-hydride under extreme pressure, high electron phonon coupling coexists with high frequency phonons originating from hydrogen modes, leading to extremely high transition temperatures as predicted by Eliashberg theory. Their experimental effort showing the hallmarks of superconductivity above 200K include zero resistance, Meissner shielding, and an isotope effect, and make a compelling case for superconductivity.

The session was continued by the talk titled “High Temperature Superconductivity of Highly Compressed Materials” given by Katsuya Shimizu. In the talk he reported his recent results on the structure of H3S under high pressure P = 100 – 200 GPa obtained by XRD. The collected x-ray diffraction data showed good agreement with the theoretically predicted structures of R3m and Im-3m4,5. No structural difference was observed between at 10 K and room temperature. Further he reviewed his work on Ca.

In the next talk “Pairing mechanism of BiS2 superconductor: A first-principles study” Ryotaro Arita presented theoretical ab initio calculations of the critical temperature of novel BiS2-based layered superconductors, which are attracting broad interest. He described his new method of first principle calculation and showed that conventional phonon-mediated pairing cannot explain the high superconducting transition temperatures observed in this material.

The last talk of the session titled “Emergent electronic phenomena in π-electron molecular systems” was given by Kosmas Prassides. The first part was devoted to the investigation of C60-based solids with stoichiometry A3C60 (A = alkali metal), which display the highest upper critical magnetic field (Hc2 > 90 T) among all known three-dimensional superconducting solids.
The second part of the talk was devoted to synthesis of f ionic salts of polyaromatic hydrocarbon. Whereas Cs2(C14H10) is diamagnetic due to orbital polarization, Cs(C14H10) is a Heisenberg antiferromagnet with a gapped spin-liquid state emerging from the coupled highly frustrated Delta-chain magnetic topology of alternating-exchange spiral tubes of S = ½.

Prof. X.X. Xi(Temple University, USA) talked about “MgB2 thin films for SRF cavity applications”. Prof. Xi mentioned that clean MgB2 thin films have a low residual resistivity and high Tc of ~40K and are promising materials to RF cavity applications if we can obtain Hc1 values higher than that of Nb. He has been studying MgB2 thin films applying a hybrid-physical-chemical vapor deposition(HPCVD) method. He succeeded in obtaining high Hc1 of MgB2 film, higher than that of Nb by decreasing the film thickness. He also carried out the deposition of MgB2 film on Cu, which is important to cavity application. He observed the formation of Mg-Cu compound layer between Cu substrate and MgB2 film. He also observed the cracks introduced into the MgB2 films after the deposition. He mentioned that these cracks are due to the difference of thermal contraction between Cu and MgB2. He also carried out the coating of RF cavities with MgB2 and investigated the properties.

S.K. Chen(University Putra, Malaysia) reported on “Synthesis and optimization of superconducting properties of MgB2”. Dr. Chen fabricated MgB2 bulks by direct reaction between Mg and B or MgB4 and Mg. He mentioned that with increasing heat treatment temperature a compromise between grain connectivity and defect density becomes crucial in order to optimize Jc. He obtained a few orders of magnitude higher Jc values by the addition of SiC nano-particles. The field dependence of Jc was improved with a slight decrease of Tc by the SiC addition. He also mentioned that addition of excess Mg to MgB4(Mg1.5B2) increased the weight fraction of MgB2 together with unreacted Mg and enhanced Jc values.

P. Badica(National institute of Materials Physics, Romania) reported on “addition, co-additions and raw materials influence on MgB2 obtained by spark plasma sintering”. Dr. Badica mentioned that high density MgB2 bulks can be obtained by spark plasma sintering(SPS). He used MgB2 powder and additives or co-additives as a raw materials. He mentioned that the type of an additive is important, but the key element is not only that. The microstructure of SPS sample seems complicated. He also mentioned that the specific features of the raw powders (morphology, size, purity and so on) and processing conditions(e.g. interaction between co-additions or the mixing level of the powders) can or can’t lead to formation of pinning centers.

M. Muralidhar(Shibaura Institute of Technology, Japan) reported “low cost and high performance bulk MgB2 material for super-magnets”. Prof. Muralidhar fabricated MgB2 bulks by mixing crystalline boron and nano-meter-sized amorphous boron powders encapsulated in carbon to reduce the cost of the bulk materials. He obtained sharp superconducting transitions of with Tc,onset around 38.6-27.2K for the bulks prepared with the mixture of crystallince boron and carbon-coated amorphous boron. He mentioned that the highest Jc values of 470kA/cm2 and 310kA/cm2 in self-field and 1T, respectively, were obtained at 20K for the MgB2 sample with 1.5% of carbon in the carbon-encapsulated boron.

A3-P31-007 S. Kunwar

BCS-BEC (Bose Einstein Condensation) crossover in iron based superconductor was characterized by STM. One of the hottest topics for revealing the mechanism of the superconductivity in these materials.

A3-P31-008 C. M. Palomares-Garcia et al.

Thin film growth of Sr2RuO4 on LSAT substarate by PLD technique. Drop of the resistance was observed at around the bulk Tc.

A3-P31-009 K. Komori et. al.

Fabrication of seamless flux transformer made of a superconducting tape for magnetic measurement. Simple technique but the method is also applicable to seamless superconducting solenoid.

A3-P31-010 T. Maeda et al.

Nb-based 1212 superconductor. Nb was substituted by Cu. Impurity phases were reduced by the substitution.

A3-P31-011 T. Maeda et al.

Substitution of Y-123 superconductor. Substitution of Ba by Sr and Cu by Mo. Superconductivity at relatively higher temperature was observed even in tetragonal phase.

A3-P31-012 Y. Sanogawa

Fabrication of bulk MgB2 superconductor using vapor transport method. The amount of MgO phase can be reduced by this technique.

Keynote talk by prof. Zhao

Photo-Responsive Self-Assembled Organic Nanoparticles for Bioimaging and Therapy

As the keynote talk of our symposium, prof. Yanli ZHAO, Nanyang Technological University, Singapore, presented simple but excellent strategies to apply functional dyes to bioimaging systems on 31th Aug. The prof. Zhao’s research group have developed novel photo-responsive multifunctional nanoparticles for targeted bioimaging and controlled drug delivery in disease therapy. In order to overcome photon scattering and low optical response in biological tissues, they integrated nanoparticles as exogenous contrast agents for enhancing the capability of bioimaging modalities, and also utilized porous nanoparticles to prevent undesired aggregation of dyes. They have synthesized several types of photoresponsive nanoparticles for fluorescent and multi-photon, and photoacoustic bioimaging systems that can work in vivo. These photoresponsive nanoparticles can simultaneously target diseased cells, and enable the location to be imaged by optical methods, and release therapeutic drugs to the diseased cells by commands. The photoresponsive bioimaging and drug delivery strategies developed by the prof. Zhao’s research group could be applied to existing drugs or experimental compounds, and realize longer circulation time or better targeting. These research achievements pave the way for developing next generation of therapeutics.

1. In an invited talk entitled “Low electronic thermal conductivity and violation of the Wiedemann-Franz law in correlated metallic vanadium oxides”, Kedar Hippalgaonkar (Agency for Science, Technology and Research, Singapore) reported about a study moving from the inconsistency between the measured value of VO₂ thermal conductivity and its predicted electronic component based upon the Wiedemann-Franz law. Through independent measurements of the lattice thermal conductivity he showed how the total conductivity would be expected to be much larger than its experimental value. Doping with W recovered the expected electronic contribution, showing how the Wiedemann-Franz “constant” is here a linear function of W content. A sophisticated model explained this anomaly as due to the electronic correlation in the material, where electrons behave as a coherent/incoherent Fermi liquid.
2. Kunpeng Zhao – Cu2S has lower lattice k, Cu2Se has higher PF, what happens if we put them together, nanodomains with 20-8 0nms are formed and a modulated cubic phase is found, which is good for reducing lattice thermal conductivity. Phase transition from 300-700K giving large heat capacity below 700K… Electrical conductivity determines that the PF lies between the two materials. The carrier concentration is increased, so the seebeck drops and conductivity increases. Maximum value comes from those with Cu vacancies. Pisarenko Plot gives an effective mass of 4.2m0, but higher mobility, giving a higher weighted mobility. Low lattice conductivity (~0.3-0.4 W/m-K) with higher PF gives ZT as high as 2.3 at 1000K at 10^20-10^21 cm-3 carrier concentration. A question on stability was asked and the author showed data that the phase transition has hysteresis, but proving that there’s stability.

3.  Lanling Zhao: Investigation of TE properties of Cu2Se(S) – Liquidlike materials should have lower specific heat at higher  temperature. Increased electrical resistivity and Seebeck at higher temperatures and slightly reduced kL (~0.6 W/m-K). zT ~ 1.2 up to 1.8 (single crystals) comparable to polycrystalline bulk. Stability is not an issue for water-quenched CuSe samples. Copper deficient CuS shows increased electrical conductivity, similar kL, but smaller S. But due to larger sigma, zT is higher, but this has poor electrical  and thermal stability. Next, the author talked about Te and I doped samples and found that Te is better for electrical conductivity.  Highest ZT is for CuSe, and the Te/I doping does not help. Then, the author introduced Sulfur doped CuSe, for doping levels <0.16 where the structure remains monoclinic.  For higher doping, the samples are composite multiphase.  TE properties show lower electrical conductivity and increased Seebeck, but the CuSe ZT cannot be improved. Finally, the author introduced composites with CNTs, graphite and hard Carbon – graphite forms nanoclusters with a grain size ~30-60nms. Carbon doping gives higher sigma and comparable Seebeck and reduced kappa, obtaining higher ZT around 2.4 at 970K.
4. Terumasa Tadano – Peierls Boltzmann Theory (phonon gas model) deals with cubic anharmonic scattering. Full anharmonicity is considered in ab initio MD. The author proposed a new method to decrease computational cost, which is between BTE and ab-initio. Usually, DFT considers 2nd and 3rd order force constants, then uses BTE, neglecting 4th order anharmonicity. This breaks down when there’s an imaginary mode underlining that quartic anharmonicity is important, for eg. SnSe (TE materials) ‘soft’ materials causes frequency shift and introduce 4-phonon scattering. The author uses Self-Consistent Phonon Theory to obtain an effective Hamiltonian to obtain a temperature dependent phonon dispersion. Inelastic Nuetron Scattering (INS) experimentally corroborates this. Tested on cubic STO.T-dependent phonon dispersion but PbTe and SnSe show very strong temperature dependence due to more soft modes. Hence, this allows for self-corrected phonons to be added to a BTE calculation, and the key is to use 2nd and 4th order force constants. This calculation was also performed on clathrates (BGG), where a hardening of the rattling mode is observed. These rattling modes scatter acoustic phonons and hence the details are important resulting in an enhancement in lattice thermal conductivity due to quartic anharmonicity. Software is now available at ALAMODE at http://ttadano.github.io/alamode/