Crystal chemistry and physical properties of the ternary compounds R10B9C12 (R = La, Ce, Pr, Nd)

The ternary rare earth boride carbides R10B9C12 (R = La, Ce, Pr, Nd) were synthesized by reacting the elements at temperatures between 1470 and 1760 K. The crystal structures (Ce10B9C12 type) were determined from single crystal X-ray diffraction data. For Pr10B9C12 we found: space group P41212, Z = 4, a = 8.4365(3) Å, c = 25.468(1) Å (R1 = 0.023 (wR2 = 0.044) from 2315 reflections with Io > 2σ(Io)); for Nd10B9C12, a = 8.3834(3) Å, c = 25.352(1) Å (R1 = 0.021 (wR2 = 0.044) from 1847 reflections with Io > 2σ(Io)). The three-dimensional network of rare earth atoms resulting from a stacking of slightly corrugated square nets has its voids filled with B4C4 and B5C8 finite chains. The lattice parameters of the isostructural compounds, formed with La and Ce, were refined from powder X-ray diffraction data. Magnetic properties are reported for all compounds. La10B9C12 is a temperature independent paramagnet down to 6 K. The remaining compounds show a tendency of ferromagnetic ordering at T < 10 K at elevated external fields (induced ferromagnets). The electrical resistivity for Ce10B9C12 reveals a weak metal-like temperature dependence below room temperature. From heat capacity measurements it can be concluded that the magnetic order is rather a short range type ordering and field induced in the case of Ce10B9C12 and Pr10B9C12.

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