Preparation and physical properties of rare earth hexaborides and dodecaborides

Abstract

The rare earth hexaborides and dodecaborides have been prepared using a floating zone technique.The rare earth hexaborides exhibit a variety of physical properties ranging from superconductor (YB6), to typical monovalent metal (LaB6), dense Kondo system (CeB6), valence fluctuating system (SmB6), anomalous magnetism based on the narrow gap semiconductor (EuB6), and nonmagnetic narrow gap semiconductor (YbB6).From the measurements of the magnetic susceptibility, electrical resistivity, Hall effect, NMR, XPS and specific heat measurement, it is found that YbB12 exhibits unique behavior uncharacteritic of hitherto studied ytterbium compounds; YbB12 is a mixed valent compound accompanied with the formation of an energy gap. LuB12 is a monovalent metal similar to LaB6.