${\mathrm{LaB}}_6$ and other hexaborides are inclusion compounds in which the rare earth or other metal ion is weakly bound and sits in an oversized “cage” of boron ions. Here we show that a simple model that treats the La ions as independent harmonic (Einstein) oscillators embedded in a Debye framework of boron ions successfully accounts for the anomalies in the specific heat and resistivity of ${\mathrm{LaB}}_6.$ One of the nice features of the model is that the Einstein temperature of the La atoms and the Debye temperature of the boron framework are derived from room-temperature x-ray crystallography data. This feature makes the model easy to apply to other hexaborides and other materials that can be treated as inclusion compounds. The results from this work imply that local modes are likely to be important for understanding the physical properties of all the hexaborides.

• Received 22 December 2000

DOI:https://doi.org/10.1103/PhysRevB.64.012302