Dynamic Observation of Incommensurate Phases by High Resolution Electron Microscopy

Research Project

Project/Area Number	60540197
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	固体物性
Research Institution	Tokyo Institute of Technology
Principal Investigator	YAMAMOTO Naoki Tokyo Institute of Technology, 理学部, 助手 (90108184)
Project Period (FY)	1985 – 1986
Project Status	Completed (Fiscal Year 1986)
Budget Amount *help	¥1,600,000 (Direct Cost: ¥1,600,000) Fiscal Year 1986: ¥600,000 (Direct Cost: ¥600,000) Fiscal Year 1985: ¥1,000,000 (Direct Cost: ¥1,000,000)
Keywords	Electron Microscopy / Cooling Holder for TEM / Incommensurate phase / 整合-不整合相転移 / ディスコメンシュレーション
Research Abstract	The incommensurate (IC) phases have been found in many types of materials, which have recently become a subject of special interest. Since many of the IC phases exist below a room temperature, we specialy need a cooling holder for transmission electron microscopy (TEM), which makes it possible 1) to cool down a specimen at least up to near the Liq. <N_2> temperature, and 2) to observe the fine structures of the IC phases in nm scale. The purpose of this project is 1) to equipe a commercial cooling holder completely for observations in high resolution, and 2) to apply it for studies of the IC phases. This project lasted for two years. We purchased a commercial cooling holder in the first year, and have used it for observing the IC phases in sevral materials with improving its capability. The cooling holder has a Liq. <N_2> reservoir tank and a specimen can be cooled down by heat conduction from the reservoir. This holder is a side-entree type, having a double tilting mechanism which is efficient to get crystallographic informations in TEM. As for the ability of the holder in the present stage, it can cool a specimen down to -150 ゜C and change a specimen temperature in the range between -150 ゜C to 25 ゜C. The resolution of the TEM images taken with an exposure time of a few seconds is 1.2 nm. We studed mainly <Rb_2> <ZnCl_4> using the cooling holder, since this material has an IC phase between 30 ゜C and -81 ゜C and was just reported to be observable by TEM in the International Meeting on Ferroelectricity (1985). One dimensional array of "discommensurations (DC's)" was observed in the IC phase. It was found that there are two types of DC's which correspond to domain walls of the commensurate phase. We also found "dislocations" of the DC lattice composed of 6 DC's, and observed their creation and anihilation processes with chaging temperature in the IC phase.