报告摘要：

Topic 1

The effect of room-temperature high-pressure (RTHP) treatment on the transport properties, crystal structure, and electronic structure of CuGaTe₂ with chalcopyrite structure were investigated. The thermal conductivity of RTHP-treated CuGaTe₂ is greatly reduced, which is attributed to the point defects, stacking faults, and increased grain boundaries from the results of theoretical analysis based on the Callaway model. These defects also decrease the carrier mobility and increase the carrier concentration, resulting in lowering the electrical conductivity and Seebeck coefficient of RTHP-treated CuGaTe₂. The crystal structure analysis indicates that RTHP-treated CuGaTe₂ contains microstrains, which partially arises from a series of disorder at the Cu-Ga cation site with a variety of degrees and geometries. We predicts, from the calculated formation energy, that such disorder can be induced as a metastable structure evolved by the RTHP-treatment applied in this study. Electronic structure calculations clarifies that the disorder at the Cu-Ga cation site changes orbitals hybridization near the Fermi energy. Specifically Cu 3d orbital and Te 5p orbital approach to the Fermi energy from the conduction band, which contributes to decease in the band gap, resulting in bipolar conduction. This calculation result is consistent with the experimentally observed increase in carrier concentration and decrease in Seebeck coefficient.

Y. Fujii and A. Kosuga et al., Outstanding Poster Award in ICT2016.

Y. Fujii and A. Kosuga et al., in preparation for submission.

Topic 2

Polycrystalline CuGaTe₂ with a chalcopyrite-type structure consolidated by hot-pressing is a potential candidate as a medium temperature thermoelectric (TE) material. However, its high-temperature formation phases have rarely been reported to date. Here, we investigated the temperature dependent formation phases and crystal structure at 300–800 K of hot-pressed CuGaTe₂. From synchrotron X-ray diffraction data and crystal structure analysis of the heating and cooling processes, it was clarified that a certain amount of impurity phases, such as Te and CuTe, precipitated from the CuGaTe₂ matrix when the temperature was increased to 500–650 K. This is the temperature range where CuGaTe₂ has been reported to show high TE performance. After CuGaTe₂ was heated to 800 K, such impurity phases remained, even when cooled to room temperature. They also affected the tetragonal distortion and x-coordinate of Te in the CuGaTe₂ matrix, probably due to deficiencies of Cu and Te in the matrix. Our results reveal detailed information on the formation phases of CuGaTe₂ at high temperature and, thus, provide insight for evaluation of its high-temperature stability and transport properties.

Y. Fujii and A. Kosuga, Journal of Electronic Materials in press.

报告人简介：

Name: Atsuko KOSUGA

Address(Office): Department of Physical Science,

Graduate School of Science,

Osaka Prefecture University,

Gakuencho 1-1, Nanaku,

Sakai, Osaka 599-8531, Japan

Phone& Fax: +81-72-254-9826

E-mail : a-kosuga@p.s.osakafu-u.ac.jp

EDUCATION

March 2000 Bachelor of Engineering,

Department of Electronic, Information Systems and Energy Engineering, Graduate School of Engineering, Osaka University, Japan

March 2002 Master of Engineering,

Department of Nuclear Engineering, Graduate School of Engineering, Osaka University, Japan

July 2006 Ph. D.in Engineering, Osaka University (Supervisor: Prof. Shinsuke YAMANAKA)

WORKINGEXPERIENCE

April 2002-April 2003

Researcher at Murata Manufacturing Co., Ltd.(Japan)

・Development of electronic devices

May 2003 -March 2006

COE Assistant Professor at Osaka University(Japan)

Project: 21stcentury center of excellence towards creating new industriesbased on inter-nanoscience

・Synthesis and physical property investigation of energy related materials (thermoelectric, photocatalyst, and nuclear materials)

July 2006 -October 2006

Technical Staff atNational Institute of Advanced Industrial Science and Technology (Japan)

・Synthesis and physical property investigation of thermoelectric oxides

・Development of thermoelectric oxide modules

April 2007 –March 2010

Research Fellow of the Japan Society for the Promotion of Science (JSPS) for Young Scientistsat National Institute of Advanced Industrial Science and Technology (Japan) (Supervisor: Dr. Ryoji FUNAHASHI)

・Synthesis and physical property investigation of thermoelectric oxides

・Development of thermoelectric oxide modules

April 2012-March 2016

Special Lecture (Tenure-track Lecture) at Thermoelectric Group, Nanoscience and Nanotechnology Research Institute,Research Organizationfor the 21stCentury, Osaka Prefecture University(Japan)

・Development of high-efficient thermoelectric materials by nanostructure control・Development of eco-friendly ceramic thermoelectric materials

April 2016-Present

Tenured Associate Professor at Thermoelectric Group, Department of Physical Science, Graduate School of Science, Osaka Prefecture University (Japan)

・Study on crystal structure and transport propertiesof novel thermoelectric materials

・Development of thermoelectric materials with new function

October2017-Present

PRESTO Researcher, Japan Science and Technology Agency, Japan

・Development of thermoelectric materials and modules based on GeSbTe materials

AWARD

1. The Best Scientific Paper Award from the International Thermoelectric Society (June 2005)

2. The Best Paper Award from the Thermoelectric Society of Japan (August 2008)

3. The Best Poster Award from the Thermoelectric Society of Japan (August 2012)

4. The Award for Encouragement of Research in IUMRS-ICA2014 from IUMRS-ICA (October 2014)

5. The ITS Outstanding Poster Award from the International Thermoelectric Society (June 2016)

6. The Best Poster Award from the Thermoelectric Society of Japan (September 2016)

7. The Best Poster Award from the Japan Institute of Metals and Materials (September, 2016)