Crystal chemistry and physical properties of the ternary compounds RE5B4C5 (RE=Ce, Pr, Nd) Original Research Article

The ternary rare-earth metal boride carbides RE5B4C5 (RE=Ce, Pr, Nd) were prepared by arc melting the mixtures of the pure elements and subsequent annealing at 1270 K. Their crystal structures were determined from single crystal X-ray diffraction data. They crystallize in the Ce5B4C5 type of structure (space group Pna21, Z=8). Two new compounds were found, Pr5B4C5: a=24.592(2) Å, b=8.4563(5) Å, c=8.4918(5) Å, R1=0.043 (wR2=0.076) for 2871 reflections with Io⩾2σ(Io)); for Nd5B4C5: a=24.301(1) Å, b=8.3126(5) Å, c=8.3545(4) Å, R1=0.035 (wR2=0.069) for 3707 reflections with Io⩾2σ(Io)). Its structural arrangement consists of a three-dimensional framework of rare-earth atoms resulting from the stacking of slightly corrugated two-dimensional square nets, leading to voids filled with B4C4, B3C3, BC2 finite chains and isolated carbon atoms. Ce5B4C5 is an antiferromagnet at 5 K followed by a metamagnetic transition in elevated external fields. Pr5B4C5 and Nd5B4C5 are ferromagnets below TC=12 and 15 K, respectively.