Month: August 2017

Prof. Thimont made an invited talk about their special processing technique for making higher manganese silicide.

Prof. Ikeda, who is the other invited speaker, introduced the technique for making super-saturated solid solutions and nano-sized precipitates in the Si-based materials.

Two of the contributed talks were made by students, Mr. Alinejat and Mr. Takamatsu, and they made nice talk about synthesis technique of Mg2Si and thermoelectric properties of CrSi2 based C40 phase, respectively.

The number of attendee was roughly thirty, and all the talk had many questions.

 

 

High thermoelectric performance in Te-free (Bi, Sb)₂Se₃ (Keynote)

This presentation discussed (Bi,Sb)2Se3 as an affordable material for energy harvesting in the low to mid-range of temperatures. Rhombohedral Bi2Se3 is isostructural with the telluride whereas orthorhombic Sb2Se3 has a chain like structure. Investigation of the pseudo-binary Bi2Se3-Sb2Se3 phase diagram was reported and shown to consist of two single phase R and O regions, separated by a two-phase region. The RO structural change impacts on both electronic and dynamical properties and ZT=0.3 may be attained in O-(Bi,Sb)2Se3. Further improvements in charge carrier concentration through iodine doping raises this to 1.0 at 800 K.

Open die pressing of thermoelectric materials: a solution for material sintering and texture inducing (Invited)

This presentation focused on how to achieve single-crystal–like transport properties in polycrystalline phase through a new processing method, which seeks to exploit structural anisotropy to texture the material. Processing consists of hot-pressing powders contained within a metal sheath for relatively short periods at modest temperatures. (Bi,Sb)Te3 and SnSe were presented as examples. Although an observable degree of texturing was achieved in the latter, single-crystal levels of anisotropy in the properties have not yet been realised. The method was also shown to provide a one-step synthesis and consolidation process for the preparation of nickel-substituted tetrahedrite.

Enhanced thermoelectric performance of p-type MnTe doped with Ag

Maximizing thermoelectric performance of PbSe by combining non-stoichiometric composition optimization and alloying with SnSe

Last two talks were presented from the same group in Tsinghua University, China. They made tellurides, and enhance the thermoelectric properties well by doping. Tellurium is well known one of rare earth materials. They made thermoelectric materials by replacing tellurium to selenium to reduce tellurium consumption. Lead is one of the strong toxic materials. Lead is also replaced to Sn for a practical use of thermoelectric materials. The research group showed us the possibility of atomic substitution for thermoelectric materials without ZT huge reduction.

A packed conference room for Session A-5

Room1 / THIN FILMS, MULTILAYERS, NANOSTRUCTURES I

Prof. Chunlei Wan (Tsinghua University, China) presented high-performance inorganic / organic superlattices for flexible thermoelectric energy harvesting.

The authors showed thermoelectric properties of organic molecule cation intercalated TiS2 (electrochemically), which looks like superlattice (layered structure). They successfully reduced the thermal conductivity while maintain its rather high electrical conductivity. Positively charged organic cations play several important roles such as good donor (strong positive electric field), enhancement of two-dimensionality, and reducing agent of thermal conductivity.

Prof. Kyu Hyoung Lee (Kangwon National University, Korea) presented design and preparation of high performance thermoelectric materials with defect structures.

The authors showed interesting way to enhance thermoelectric figure of merit of several materials such as BiSbTe, BiTeSe, and half-Heusler. They successfully reduced the thermal conductivity by introducing dislocation arrays at around the grain boundaries. They achieved 30-50% enhancement of their zT.

Chairpersons: Akiyasu YAMAMOTO and Valeria BRACCINI

A3-K30-001 Keynote
Vortex Pinning in iron based superconductors
Kees VAN DER BEEK

Jc and Hc2 in IBS look very interesting but way lower than in HTS (in particular in YBCO): the phase 1111 is the better performing in this respect. Flux pinning mechanisms look similar in all IBS, and have been extensively studied and presented in this talk.

Pinning centers can be nm-size inclusions, dislocations or Fe vacancies (in particular in FeSe single crystals, see very recent work by Sprau et al., 357 (2017) 65).

Jc vs field has been extensively investigated, and presents a similar behaviour in various materials. After a plateau where Jc is constant, it decreases proportionally to B^-0.5, then again it smoothest down. At low field it is predominant the contribution from big grains, isolated vortices (strong pinning on a nm scale), at intermediate fields we have collective pinning due to charged dopants / vacancies.

The depairing current density has been investigated: it presents a dome as a function of the doping, as it happens for the Tc vs x.

Vortex pinning has been correlated to the behaviour of .
The multiple band character of superconductivity has a strong influence on Jc and on its anisotropy, which in particular in the ab direction is strongly related to the anisotropy of .

A3-I30-003 Invited
Arsenic Chemistry of Iron-based Superconductors and Strategy for New Superconducting Materials
Minoru NOHARA

Prof. Nohara reported the progress of iron-based superconducting materials with the emphasis on the valence states and chemical bonds of arsenic. They demonstrated that in the novel 112-type CaFeAs2, monovalent arsenic produced As zigzag chains of CaAs intermediary layers, while trivalent arsenic produced FeAs layers. The superconducting transition temperature of this materials was enhanced up to 47 K when La and Sb were simultaneously substituted for Ca and As, respectively. Sb is preferably substituted for the As of the zigzag chains. On the other hand, in the 10-4-8-type Ca10(Pt4As8)(Fe2−xPtxAs2)5 with the highest Tc of 38 K, he emphasized that divalent arsenic produced As2 dimers in Pt4As8 layers. Finally, he discussed the structural phase transition in 122-type CaFe2As2 that is characterized by the formation of As2 dimers between the adjacent FeAs layers, which resulted in the loss of magnetism and disappearance of superconductivity. This transition can be viewed as an As2-/As3- valence transition.

A3-I30-002 Invited
Doping dependent critical current properties in K, Co, and P-doped BaFe2As2 single crystals
Hiroshi EISAKI

Dr. Eisaki reported the in-plane critical current density (Jc) of BaFe2As2-based superconductors, Ba1-xKxFe2As2 (K-Ba122), Ba(Fe1-xCox)2As2 (Co-Ba122), and BaFe2(As1-xPx)2 (P-Ba122) in a wide range of doping concentration (x) by means of magnetization hysteresis loop (MHL) measurements on single crystal samples. Depending on the dopant elements and their concentration, Jc exhibits a variety of magnetic-field (H)- and temperature (T)- dependences. In the case of K-Ba122, the MHL of the under-doped samples (x < 0.33) exhibits the second magnetization peak (SMP), which sustains high Jc at high H and high T, exceeding 105 A/cm2 at T = 25 K and μ0H = 6 T for x = 0.30. On the other hand, the SMP is missing in the optimally- (x ~ 0.36-0.40) and overdoped (x ~ 0.50) samples, and consequently Jc rapidly decreases by more than one order of magnitude, although the change in Tc is within a few K. He pointed out that the T-dependent Jc indicates that the two pinning mechanisms, namely, the spatial variations in Tc (referred to as delta-Tc pinning) and the fluctuations in the mean free path (delta-l pinning), are enhanced for the under-doped samples, which results in the enhancement of Jc. Possible origins for the different pinning mechanism are discussed in connection with the x-dependence of Tc, the residual resistivity, AFO domain boundaries, a possible quantum critical point, etc.

A3-K30-004 Invited
Pressure Effects of FeSe by Novel DAC using metallic Diamond Electrodes
Yoshihiko TAKANO

A deep work published very recently (Matsumoto et al., JJAP 56 (2017)) has been presented, regarding the pressure effects induced in FeSe single crystals by a novel Diamond Anvil Cell.

Superconducting properties of many different materials under high pressure have recently received great attention, especially after the discovery with great surprise of superconductivity in H2S at ∼200 K under 150 GPa which was reported by resistivity measurements using a diamond anvil cell (DAC) in 2015. In fact, if one can measure the resistivity under extremely higher pressure above 300 GPa, superconductivity at room temperature in light elements such as hydrogen would be observed.
The resistivity measurement though is difficult because the sample space is very small (<100 μm) and the electrodes are deformed by compression. A novel diamond anvil cell specialized for resistivity measurements under high pressure has been developed at NIMS, Tsukuba. Once metallic diamond is heavily boron-doped, it shows metallicity and superconductivity at low temperature. Boron-doped metallic diamond electrodes were deposited onto a diamond anvil using a electron beam lithograph: in this way, resistivity measurements can be performed up to 10 GPa.

In particular, results obtained through this technique on FeSe single crystals have been reported. FeSe shows a Tc of 8 K, which can increase up to 37 K with the application of idrostatic pressure (8 GPa). When uniaxial pressure is applied, at NIMS they were able to reach Tc as high as 44 K, similarly to what happens in FeSe phase after K intercalation. This Tc increase depends on the anion height from the Fe layer which can be changed through the intercalation or through the application of the uniaxial pressure.

Structure and physical properties of polymers in confined systems

We continued active discussion on structure and properties of nanoscale polymeric materials in confined system, quantum beam analysis of polymer structure and dynamics and novel polymer processing technology through the third day. We had more than 50 participants in each presentation. “Langmuir Award” and “Soft Matter Award” were provided to our symposium by courtesy of the ACS publications and Royal Society for Chemistry. The presentations, which is given by young researchers, were judged by the aid of invited speakers of our symposium and the symposium organizers (totally 17 reviewers from 5 countries) have selected following four award winners.

Congratulations!!

Langmuir Award

C2-P28-011
Aggregation States of Polymer Inclusion Complexes at Water Interface
Hidenobu TANEDA(Kyushu University, Fukuoka, Japan)

C2-P28-005
Precise Synthesis of Stereoregularity-controlled PMMA-b -PDMS-b -PMMA and Characterization of Its Molecular Aggregation Structure
Hitoshi SHIMAMOTO(Kyushu University, Fukuoka, Japan)

Soft Matter Poster Award

C2-P28-023
Preparation of High-Density Polyethylene Nanocomposites Well Reinforced by Cellulose Nanofiber Using Diblock Copolymer-type Dispersants
Keita SAKAKIBARA(Kyoto University, Uji, Japan)

Soft Matter Presentation Award

C2-O30-019
Interfacial Modifications of Thin Films by　Preferential Segregation of Janus Macromolecules
Yukari ODA(Kyushu University, Fukuoka, Japan)

After the final day of session C-2. Many people stay until the end of the session.

The symposium D-2 oral session started from August 30. The organizer (Prof. Toshihiro OKABE) introduced significance of this  symposium. There has been a strong demand for environmentally friendly product in the globe. This session aim to promote environmentally friendly products.

In the morning on August 31(2nd day), we had 3 oral papers and 2 invited lectures. In invited lectures,Tongxiang FAN of School of Materials Science and Engineering ,Shanghai Jiaotong University, “R&D of wood ceramics and porous carbon in China”. In China,18 universities and 1 institute are researching in these grounds. He introduced the characteristics of research about 7 universities and 1 institute.

Kanehiko UTSUNO of Jingushicho explained about the sanctuary reconstruction in the Shikinen Sengu of Ise Jingu. He introduced the history, the method of reconstruction, the reuse of old wooden building materials, the prevention of corrosion and the lasting for  wooden building materials and saw grass in the Shikinen Sengu.

In the afternoon, we had the poster session. 21poster papers were presented with active discussion and question and answer.(4 poster papers presented on August 29).

Unique Electronic Structures and Properties of Oxide Thin Films and Multilayers

There were many interesting presentations about unique electronic structures as well as magnetic and electrical properties of oxide thin films and multilayers in this symposium. The oxide compounds for which the electronic structures and properties were reported are SrTiO₃, BiFeO₃, Bi(Fe,Co)O₃, (La,Sr)MnO₃, LaNiO₃, LaMnO₃, YBa₂Cu₃O₇, Y₃Fe₅O₁₂, Gd₃Ga₅O₁₂, Y(Mn,Cr)O₃, LaCa₂Fe₃O₈, SrRuO₃. Two keynote lectures given by C. G. Van De Walle and H.-U. Habermeier clearly indicate that there exist some critical factors, which have great influence on the electrical conductivity and magnetization, such as carrier density, number of oxygen vacancy, distortion of crystal structure, strain induced in thin films. For the case of SrTiO₃ thin films which have point defects, as suggested by two invited presentations (A. Schulman and F. Gunkel), the temperature dependence of resistivity manifests the Kondo-effect-like behavior depending on the oxygen partial pressure and carrier density. The charge transfer in multilayers such as SrTiO₃/GdTiO₃ (C. G. Van De Walle, as mentioned above) and LaNiO₃/LaMnO₃ (M. Kitamura) also plays an important role to determine transport properties as well as magnetic structure. Other topics include interest magnetic domain patterns in composites between ferromagnetic metals and oxide superconductor (A. Palau), spin Hall effect and electrically driven magnetization dynamics in Y₃Fe₅O₁₂ (A. Hoffmann), and spin Seebeck effect in paramagnetic and antiferromagnetic thin films (A. Bhattacharya). There were many active discussions about those topics concerning magnetic oxide thin films and hetero-structures.

A scene of symposium A-4

This session was planned to discuss various possibilities for the sudden rise in advanced ceramics and glasses extensively from the viewpoint of structural formation.
We had 10 invited talks, 13 oral presentations, and 24 poster presentations. The speakers came from China, Taiwan, Korea, Thailand, Mexico and Japan. On the 1st day evening and the 3rd day afternoon, we had poster session. Young students and middle-aged experts (professors, research experts) were mixed there and enjoyed their discussions. Some photos are shown below.
Finally, all the organizers greatly expressed their gratitude to all poster presenters of this session, and also organizing committees of IUMRS-ICAM2017.

Fig.1 Group Photo of Mexico attendees.

 

 

 

 

 

 

 Fig.2 Poster presenter from Taiwan.

 

 

 

 

 

 

Fig.3 Poster presenter from Taiwan.

 

 

Talk by Prof. Anil P S KUMAR (MRS India)

Granularity controlled topological phase

Prof. Anil P S KUMAR from Department of Physics, Indian Institute of Science, Bangalore, India, delivered a review talk for granular topological insulators. In this symposium, a focused session for topological materials was arranged inside and Prof. Xi Dai from Institute of Physics, Chinese Academy of Science shortly reviewed the progress of research of topological materials, followed by several invited talks for theoretical and experimental studies. The topological material is expected to be useful in technologies especially for quantum computing and highly sensitive magnetic sensors, although it has not been practical for many years. However, recent progress of materials development of topological insulator makes the situation changed. In the early generation of topological materials nearly massless and very fast electrons run only on the surfaces and edges of materials; however, recent topological materials show unique and useful transport properties of bulk, suggesting increasing possibilities for applications. In this session, audiences reviewed recent progress of theoretical and experimental studies of topological materials.