Preparation of Single Crystals of a New Compound, Ta5B6 by the Aluminium-Flux Method

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Abstract
Single crystals of a new compound Ta5B6 was prepared by the high temperature aluminium solution method using tantalum and boron powder as starting materials in an argon atmosphere. The experimental conditions for obtained single crystals of relatively large size were established. The optimum conditions for growing Ta5B6 single crystals were found to include atomic ratios of starting materials B/Ta=1.2 and Al/Ta=8.38, soaking temperature 1650°C, soaking time 5 h and a cooling rate of 25°C h−1. Single crystals of Ta5B6, having a grey color and metallic luster, were generally obtained in the form of an irregular or trapezoidal shape: the latter crystals were enclosed by two large {010} planes. The largest crystals prepared have maximum dimensions of about 0.12mm×0.13mm×0.23mm. The crystals are orthorhombic with a space group of either Cmm2, Cm2m, C222, or Cmmm and the unit cell dimensions a=3.1385(10) Å, b=22.609(7) Å, c=3.2865(8) Å, and V=233.20(12) Å3. The X-ray density is 13.808(2) g cm−3. The present study of growing Ta5B6 crystals is the first single crystal growth study of a V5B6 type crystal.