Crystal growth of a new aluminum sodium boride NaAlB14 and some properties

Single crystals of a new ternary boride NaAlB14 were obtained from the Na-Al-B system using a high-temperature Al self-flux under an Ar atmosphere. The reagents used to prepare the samples were Na2B4O7 powder, crystalline boron powder and Al metal chips. The optimum conditions to obtained relatively large crystals were found to include soaking temperature 1573 K, soaking time 1 h, cooling rate 50 K/h and the atomic ratios (n = B/Na = 1.0–4.0) of starting materials. The NaAlB14 crystal prepared had maximum sizes of approximately 7.3 mm × 3.3 mm × 2.8 mm. The crystals were generally obtained in the form of plate-like crystals with well-developed {0 1 0} faces or trapezoidal-shape crystals enclosed by {1 0 0}, {0 1 0}, {0 1 1} and {0 0 1} faces, and were reddish black with a metallic luster. The values of Vickers microhardness are in the ranges of 23.3 ± 1.0 and 28.4 ± 0.6 GPa for {1 0 0} and {0 1 0} faces, respectively. The susceptibility does not show any particular features, but an increase at low temperatures is indicative of a paramagnetic contribution.