CRYSTAL-GROWTH AND SOME PROPERTIES OF LUB4, LUALB4, AND LU2ALB6

Crystals of LuB4, LuAlB4, and Lu2AlB6 were grown by the high-temperatu re aluminium solution method using lutetium oxide and crystalline boro n powders as starting materials. The growth conditions for obtaining s ingle crystals of relatively large size were investigated. The as-grow n LuB4, LuAlB4, and Lu2AlB6 crystals were subjected to chemical analys is and measurements of unit cell parameters. The Vickers microhardness and electrical resistivity of the crystals were measured, and oxidati on at high temperature in air was studied. Average values of Vickers m icrohardness (Hv) and electrical resistivity (rho) determined for LuAl B4 and Lu2AlB6 single crystals areas follows: for LuALB(4) Hv = 14.0(/-0.6) GPa, rho = 86(+/-6)mu Omega . cm, and for Lu2AlB6 Hv = 18.9(+/- 0.7) GPa, rho = 31(+/-3) mu Omega . cm. The oxidation of LuB4, LuAlB4, and Lu2AlB6 crystals begins to occur at about 590 degrees C, 960 degr ees C and 1030 degrees C, respectively. The final oxidation products o f LuB4 include LuBO3 and probably amorphous B2O3 or H3BO3 However, the oxidation products of LuAlB4 and Lu2AlB6 crystals were not detected b y powder X-ray diffraction, probably due to insufficient amounts of th ese oxidation products.