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Abstract
The modulated crystal structure of Bi2.12Ba2.00Rh1.95Ox has been elucidated by electron diffraction measurements and high-resolution electron microscopy (HREM). The crystal structure consists of two interpenetrating subsystems of a CdI2-type RhO2 layer and a distorted four-layered rock-salt (RS)-type block. Both subsystems have common a- and c-axes and β-angle with a = 5.38 Å, c = 15.15 Å and β = 95.3°. On the other hand, the crystal structure is incommensurate along the b-axes; b1 = 3.05 Å for the RhO2 layer and b2 = 5.45 Å for the RS-type block. The misfit ratio and the chemical composition ratio give a chemical formula of [(Bi1−xRhx)2(Ba1−yBiy)2O4+δ]0.56RhO2 with x = 0.037, y = 0.047 and δ = 0.39. It is found that this compound has two modulation vectors, and
and, thus, can be regarded as (3 + 2)-dimensional crystal. The vector q1 is due to the misfit between the rock salt and RhO2 layers parallel to the b-axis. The modulation vector q2 is unique for the Ba–Rh system relative to Bi1.91Sr2.0Rh1.77Ox and [Bi0.87SrO2]2[CoO2]1.82. An additional modulation vector,
, is locally observed. High-resolution images, taken with the incident electron beam parallel to the a- and c-axes, clearly exhibit modulated atomic arrangements.
Acknowledgements
This study was partly supported by the CREST Project of JST and also by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan.