Neutron Powder Diffraction on Ce^<b>11</b>B_<b>2</b>C_<b>2</b>and Nd^<b>11</b>B_<b>2</b>C_<b>2</b>: A New Model for the Tetragonal Crystal Structure

Abstract

Crystal structures of CeB 2 C 2 and NdB 2 C 2 were investigated by means of neutron powder diffraction using 11 B enriched samples. Diffraction patterns of Ce 11 B 2 C 2 and Nd 11 B 2 C 2 are very similar to each other, and Rietveld analyses reveal that the crystal structure belongs to a symmetry group of tetragonal P 4/ m b m , where the rare earth atoms occupy 2( a ) sites and the B and C atoms occupy two 4( h ) sites with different positional parameters. The newly determined structure differs from previously reported ones with P 4/ m b m and \(P{\overline 4}2c\) mainly in the site positions occupied by the B and C atoms. The B and C atoms form network planes consisting of non-regular squares and octagons.