Direct observation of the microstructure in cluster glass compound U ₂IrSi₃

We have examined the structure of a U₂IrSi₃ compound exhibiting ferromagnetic cluster glass behaviour by means of electron diffraction observation and high-resolution electron microscopy. The structure of U₂IrSi₃ has been proposed as a new one of the U ₂RuSi₃-type with a short-range ordered double stacking sequence of the U₂RuSi₃-type structure along the c-axis, and long-range ordered atomic arrangements in the a-bplane. The calculated patterns reproduce the characteristic features of observed electron patterns well. The Fourier-filtered high-resolution image clearly exhibits a micro-domain structure, which is considered to relate directly to the origin of the observed cluster glass behaviour in U₂IrSi₃.