Growth of Boron Carbide Crystals from a Copper Flux
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1164-L06-02
Growth of Boron Carbide Crystals from a Copper Flux Yi Zhang1, J.H.Edgar1, Jack Plummer1, Clinton Whiteley1, Hui Chen2, Yu Zhang2, Michael Dudley2, Yinyan Gong3, James Gray3 and Martin Kuball3 1 Department of Chemical Engineering, Kansas State University, Manhattan, KS, 66506 2 Department of Materials Science and Engineering, Stony Brook University, Stony Brook, NY, 11794 3 H.H.Wills Physics Laboratory, University of Bristol, Bristol, BS8 1TL, United Kingdom ABSTRACT Boron carbide crystals ranging in size from 50 microns to several millimeters have been grown from a copper-boron carbide flux at temperatures from 1500°C to 1750°C. The crystal size increased with growth temperature although copper evaporation limited growth at the higher temperatures. Synchrotron X-ray Laue patterns were indexed according to (001) orientation boron carbide structure, indicating the bulk crystals were single crystalline with {001} growth facets. Raman spectrum of boron carbide indicates an improved crystal quality compared to the source powder, but peaks of crystals grown from 11B -enriched source shifted to the lower energy by 1-4 cm-1 from literature values, possibly due to the boron isotope dependency. Five fold symmetry defects and twin planes were common as observed by optical microscope and scanning electron microscope. Raindrop shape etch pits were formed after defect selective etching in molten potassium hydroxide at 600°C for 6 minutes. Typically, the etch pit density was on the order of 10 6 /cm2. INTRODUCTION Boron carbide is a good candidate for nuclear applications, such as neutron shielding and neutron detection due to the high neutron absorption capability of 10B, which has thermal neutron absorption cross section of 3873 barn [1]. 10B undergoes the following neutron capture reactions when exposed to neutrons: 10 B + n → Li (0.84 MeV )+ 4He(1.47 MeV ) + γ (0.48MeV ) 10 B + n→ 7 Li (0.84 MeV )+ 4He(1.47 MeV ) The resulting large kinetic energies listed in parentheses leads to local heating of the solid. In addition, it is one of the icosahedral boron-riched solids, which have an unusual self-healing ability from radiation damage. Therefore, Emin and Aselage [2] proposed a solid-state boron carbide neutron detector by measuring the Seebeck emf induced by the neutron absorption. Robertson et al [3, 4] made a boron carbide-silicon heterojunction diode to detect neutrons by means of collecting the electrons produced by the highly energetic Li and He ions as a result of neutron capture. The properties of boron carbide are associated with its unique crystal structure. It is based on twelve-boron-atom icosahedra [5], which reside at the corners of an α-rhombohedral unit cell, and three-atom C-C-C chains lying along the rhombohedral [111] axis. Such a complicate structure makes it difficult to produce large, single crystals with low defect densities. Chemical vapor deposition (CVD) methods [6-11] have been extensively studied and developed for boron carbide production. However, for solid-state devices, high quality c
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