A neutron-diffraction study of the tetragonal crystal structures of some yttrium-holmium dicarbides

Crystal structure line profile refinements have been made for neutron powder diffraction data collected at room temperature from the ternary yttrium-holmium dicarbides Y x Ho 1− x C 2 , with x = 0.75, 0.50, and 0.25, and the binary dicarbides YC 2 and HoC 2 . The five compounds are isostructural, with tetragonal unit-cell dimensions in the range a = 3.663(1), c = 6.171(1) A (for YC 2 ) to a = 3.646(1), c = 6.142(1) A (for HoC 2 ), and they contain discrete acetylenic C-C groups with carbon-carbon bond lengths close to 1.28 A.