New Ternary Compounds Sc3B0.75C3, Sc2B1.1C3.2, ScB15C1.60 and Subsolidus Phase Relations in the Sc–B–C System at 1700°C

Abstract

The phase relations in the ternary system scandium–boron–carbon with special emphasis on the boron-rich section have been investigated in an isothermal section at 1700°C. Ternary compounds with the following stoichiometries were identified: Sc2BC2, Sc3B0.75C3, Sc2B1.1C3.2, ScB2C2, ScB17C0.25, ScB15C0.80, and ScB15C1.60. Four of them, Sc3B0.75C3, Sc2B1.1C3.2, ScB15C1.60, and ScB15C0.80, were synthesized for the first time. The first three could be indexed, i.e., Sc3BC3 shows tetragonal symmetry with a=3.3308(3) Å and c=7.680(2) Å; the basic hexagonal unit cell of Sc2B1.1C3.2 is a=3.3991(2) Å, c=6.7140(6) Å, with a two-dimensional incommensurate structure with magnitude ∣qi∣=(2/7+0.005) ∣q100∣ Å−1 along 〈100〉 directions; and ScB15C1.60 shows a body centered orthorhombic lattice a=10.027(1) Å, b=8.0138(9) Å and c=5.6668(6) Å. A crystal of Sc2BC2 was grown by the floating zone method and the crystal structure was refined from single crystal data, which crystallizes with tetragonal symmetry: I4/mmm, a=3.3259(2) Å, c=10.6741(8) Å, Z=2, R=0.011 for 263 unique reflections and 10 variables.