Electron and phonon transport in single crystal tetragonal niobium bronzes

2016 Fiscal Year Final Research Report

• Project/Area Number: 26400323
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Condensed matter physics I
• Research Institution: National Institute for Materials Science
• Principal Investigator: Kolodiazhnyi Taras 国立研究開発法人物質・材料研究機構, 機能性材料研究拠点 強相関物質グループ, 主幹研究員 (80469767)
• Project Period (FY): 2014-04-01 – 2017-03-31
• Keywords: tetragonal bronze / thermal conductivity / thermoelectric power / charge density wave / anderson localization

Outline of Final Research Achievements

Solid solution of Ba6-xSrxNb10O30 crystalizes in filled tetragonal tungsten bronze (TTB) structure. Our results indicate that the Ba and Sr ions show complete solid solution without miscibility gap. We studied the x dependence of thermal conductivity of polycrystalline Ba6-xSrxNb10O30 samples measured in the 2-400 K temperature interval. Substitution of Sr for Ba brings about a significant decrease in thermal conductivity at x>3 accompanied by development of a low-temperature (T = 10-30 K) plateau region reminiscent of a glass-like compounds. We explain this behavior based on a size-driven site occupancy and atomic displacement parameters. Measurement of the electron transport of the Ba6-xSrxNb10O30 solid solution reveals an unusual metal to insulator transition which occurs upon contraction of the unit cell. Another important finding of this project was the discovery of the low-temperature superconductivity at Tc<1.6 K in the Ba-rich members of the Ba6-xSrxNb10O30 solid solution.

Free Research Field

Functional ceramics