Applied Microscopy

Korean Society of Microscopy (한국현미경학회)
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Observations on the Modulated Structure in Pyrochlore-type Compounds, $In_2(Ti_{1.7}Zn_{0.3})O_{0.67}$ and $In_2(Ti_{1.7}Mg_{0.3})O_{6.7}$

Pyrochlore형 화합물 $In_2(Ti_{1.7}Zn_{0.3})O_{0.67}$과 $In_2(Ti_{1.7}Mg_{0.3})O_{6.7}$에서의 변조구조 관찰

  • Lee, Hwack-Joo (New Materials Evaluation Center, Korea Research Institut of Standards and Science) ;
  • Park, Hyun-Min (New Materials Evaluation Center, Korea Research Institut of Standards and Science) ;
  • Cho, Yang-Koo (New Materials Evaluation Center, Korea Research Institut of Standards and Science) ;
  • Ryu, Hyun (New Materials Evaluation Center, Korea Research Institut of Standards and Science) ;
  • Nahm, Sahn (Division of Materials and Metallurgical Engineering, Korea University) ;
  • Bando, Y. (National Institute for Research in Inorganic Materials)
  • 이확주 (한국표준과학연구원 신소재평가센터) ;
  • 박현민 (한국표준과학연구원 신소재평가센터) ;
  • 조양구 (한국표준과학연구원 신소재평가센터) ;
  • 류현 (한국표준과학연구원 신소재평가센터) ;
  • 남산 (고려대학교 공과대학 재료금속공학부) ;
  • Published : 1999.12.01
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Abstract

Microstructural observations on the pyrochlore-type $Lu_2Ti_2O_7$ and the similar type of compounds, $In_2(Ti_{1.7}Zn_{0.3})O_{6.7}$ and $In_2(Ti_{1.7}Mg_{0.3})O_{6.7}$ which were made by the isothermal heat-treatment at 1623K for 18 days in Pt tube, were carried out using a top-entry HRTEM working at 200 kV. The modulated structures were found in both compounds, however, not in $Lu_2Ti_2O_7$. From the electron diffraction pattern analysis, the modulated superlattices are incommensurate and are 2.69 times of sublattices along (220) direction. The high resolution TEM images have shown that the superlattices consist of alternate superlattices which are composed of two or three sublattices, resulting in the average of 2.7 times of sublattices in accordance with the analysis of electron diffraction patterns. The crystal structures of both compounds are found to quite similar to those of pyrochlore, however the evidence that the cubic axes are slightly deviated from right angle. The modulated structure has gradually changed to the unmodulated structure induced by electron irradiation.

Pyrochlore 구조를 갖는 $Lu_2Ti_2O_7$와 그와 유사한 구조를 갖는 화합물, $In_2(Ti_{1.7}Zn_{0.3})O_{6.7}$와 $In_2(Ti_{1.7}Mg_{0.3})O_{6.7}$에 대한 미세구조 관찰을 200kV에서 작동되는 HRTEM을 이용하여 관찰하였다. 두 화합물에서는 변조구조가 관찰되었으나 pyrochlore구조인 $Lu_2Ti_2O_7$에서는 관찰되지 않았다. 전자회절패턴 분석에서는 변조구조는 incommensurate이고 [220] 방향으로 sublattice의 2.69배로 그 주기가 0.953 nm인 초격자가 관찰되었다. 고분해능 격자상에서는 sublattice의 2배 또는 3배의 초격자들로 조합되며 평균적으로 2.7배로 그 주기가 0.967 nm가 되는 초격자상이 관찰되었다. 두 화합물의 결정구조는 입방정 pyrochlore 구조와 아주 유사하나 입방정 축은 $90^{\circ}$에서 약간 벗어난 구조를 갖는다. 변조구조는 전자빔에 의하여 점차적으로 변조구조가 없는 구조로 비가역적으로 변환된다.

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