High-Resolution X-Ray Diffraction Study Of The Heavy-Fermion Compound Ybbipt

YbBiPt is a heavy-fermion compound possessing significant short-range antiferromagnetic correlations belowa temperature of T* = 0.7K, fragile antiferromagnetic order below T-N = 0.4K, a Kondo temperature of T-K approximate to 1 K, and crystalline-electric-field splitting on the order of E/k(B) = 1-10 K. Whereas the compound has a face-centered- cubic lattice at ambient temperature, certain experimental data, particularly those from studies aimed at determining its crystalline-electric-field scheme, suggest that the lattice distorts at lower temperature. Here, we present results from high-resolution, high-energy x-ray diffraction experiments which show that, within our experimental resolution of approximate to 6-10 x 10(-5) angstrom, no structural phase transition occurs between T = 1.5 and 50 K. In combination with results from dilatometry measurements, we further show that the compound's thermal expansion has a minimum at approximate to 18K and a region of negative thermal expansion for 9 less than or similar to T less than or similar to 18 K. Despite diffraction patterns taken at 1.6K which indicate that the lattice is face-centered cubic and that the Yb resides on a crystallographic site with cubic point symmetry, we demonstrate that the linear thermal expansion may be modeled using crystalline-electric-field level schemes appropriate for Yb3+ residing on a site with either cubic or less than cubic point symmetry.