2014 Fiscal Year Research-status Report
Electron and phonon transport in single crystal tetragonal niobium bronzes
| Project/Area Number |
26400323
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| Research Institution | National Institute for Materials Science |
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Principal Investigator |
KOLODIAZHN Taras 独立行政法人物質・材料研究機構, その他部局等, その他 (80469767)
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| Project Period (FY) |
2014-04-01 – 2017-03-31
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| Keywords | tetragonal bronze / thermal conductivity / thermoelectric power / metal insulator / charge density wave / Anderson localization / low-dimensional systems |
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| Outline of Annual Research Achievements |
Polycrystalline Ba6-xSrxNb10O30 solid solution was prepared. It shows complete solubility of Sr/Ba ions without immiscibility gap. It crystallizes in tetragonal tungsten bronze (TTB) structure (space group P4/mbm). The x dependence of thermal conductivity of polycrystalline samples was measured in the 2-400K temperature range. Substitution of Sr for Ba brings about a significant decrease in thermal conductivity at x>3 accompanied by development of a low-temperature (T=30K) “plateau” region reminiscent of a glass-like compounds. We explain this behaviour based on size-driven site occupancy and atomic displacement parameters associated with an alkaline earth atomic positions in the title compounds.
Moreover, single crystals of Ba6Nb10O30 and Sr6Nb10O30 were obtained by spontaneous crystallization from MgO-flux at 1400 C and 1540 C, respectively. Analysis of the x-ray diffraction data indicates that the Sr6Nb10O30 crystallizes in the lower symmetry (probably Cmcm space group) than the Ba6Nb10O30 and possibly contains an incommensurate modulation structure.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The project is progressing as planned
Several unexpected phenomena such as metal-insulator transition and low-temperature superconductivity were discovered over the course of the project. The experimental results have significantly exceeded our expectations. At the same time, each discovered phenomenon requires additional time to reach full understanding and to come up with correct interpretation.
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| Strategy for Future Research Activity |
Future steps involve:
1. Understanding of the nature of the metal insulator transition in the Ba6-xSrxNb10O30 solid solution in view of the discovered change in the crystal symmetry of the TTB structure.
2. Transmission electron microscopy and electron diffraction of the Ba6-xSrxNb10O30 solid solution in order to understand the origin of incommensurate modulation in the Sr-rich part of the solid solution.
3. Further development of the Ba-Nb-O and Sr-Nb-O ternary phase equilibria and identification of the novel ternary phases.
4. Thermoelectric and specific heat studies of the Ba6-xSrxNb10O30 solid solution in a wide temperature range of 2-1300 K.
The balance remaining from the FY 2014 research funds will be used during the FY 2015. The money will be spent on consumables, attending two international conferences and development of experimental setup.
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| Causes of Carryover |
The attendance of the Spring Meeting of the Materials Research Society and the Japanese Physical Society meetings were cancelled due to health issues. Therefore, the travel budget was not spent completely.
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| Expenditure Plan for Carryover Budget |
The balance remaining from the FY 2014 research funds will be used during the FY 2015. The money will be spent on consumables, attending two international conferences and development of experimental setup.
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