Neutron Diffraction Studies of CaC2, YC2, LaC2, CeC2, TbC2, YbC2, LuC2, and UC2

Abstract

The complete-matrix least-squares analysis on the neutron diffraction intensities of CaC2, YC2, LaC2, CeC2, TbC2, YbC2, LuC2, and UC2 yielded the C–C distances in the C2 groups, 1.191±0.009, 1.275±0.002, 1.303±0.012, 1.283±0.004, 1.293±0.009, 1.287±0.010, 1.276±0.012, and 1.340±0.007 A, respectively. The statistical averages of the neutron scattering amplitudes obtained from the dicarbide data and those reported previously are 0.488±0.007, 0.796±0.009, 0.832±0.014, 0.482±0.006, 0.756±0.020, 1.262±0.012, 0.73±0.02, and 0.851±0.022, all in 10—12 cm with positive sign, for Ca, Y, La, Ce, Tb, Yb, Lu, and U, respectively. The paramagnetic scattering analyses revealed that all metal atoms in these dicarbides are in their trivalent Hund ground state, except Ca (divalent), Yb (possible valency of 2.8), and U (possible tetravalent). The scattering data also deduced the screening constants for the 4f electrons in Ce, Tb, and Yb as 39, 43, and 43, respectively, which are compared with those obtained by other methods. The bond numbers for the rare-earth dicarbides are briefly discussed.

A comparative ab initio study of superconductivity in the body centered tetragonal YC2 and LaC2

“…All sets of parameters for both materials compare very well with their corresponding experimental values. 7,11,[24][25][26] In particular, the calculated lattice parameters (a and c) and the internal parameter (z) are in good accordance with experimental ones, 7,8,11,[23][24][25][26] with a maximum variation of 0.5%. For the bulk modulus B and its pressure derivative B 0 , the agreement with experimental results is very good for LaC 2 .…”

“…The calculated total energies are fitted to the Murnaghan's equation of state 22 to determine the bulk modulus (B) and its pressure derivative (B 0 ). The calculated values of lattice parameters (a and c), the internal parameter (z), the bulk modulus (B), and its pressure derivative (B 0 ) are presented and compared with available experimental 7,8,11,[23][24][25][26] and theoretical 10 results in Table I. All sets of parameters for both materials compare very well with their corresponding experimental values.…”

Crystal Structures of Cubic and Trigonal Yttrium Hypocarbides; A Dimorphically Interphased Single-Crystal Study

“…Therefore, because of the absence of the' paramagnetic scattering, yttrium hypocarbide should be very weakly paramagnetic or diamagnetic. The procedure of the background analysis has been fully described previously (Atoji, 1961 and1967a).…”

Crystal Structures of Cubic and Trigonal Yttrium Hypocarbides a Dimorphically Interphased Single-Crystal Study.

“…The neutron patterns w^ere of low resolution, and the overlapped peaks were resolved by means of a rather elaborate curve-fitting technique (Atoji, 1961;Atoji and Williams, I96I). A set of observed data was then subjected to numerous trial structures.…”

“…The bond numbers in YC2 (Atoji, 1961) are given in Table V for comparison. The total bond number of carbon in YC2 is larger than that in Y2C; the relation is reversed as regards the total bond number of Y.…”