Crystal growth of a new aluminum sodium boride NaAlB 14 and some properties

Abstract

Single crystals of a new ternary boride NaAlB 14 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 Na 2B 4O 7 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 NaAlB 14 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.