YbBiPt is a heavy-fermion compound possessing significant short-range antiferromagnetic correlations below a temperature of $T^{\text{*}}=0.7\mathrm{K}$, fragile antiferromagnetic order below $T_{\mathrm{N}}=0.4\mathrm{K}$, a Kondo temperature of $T_{\mathrm{K}}\approx 1\mathrm{K}$, and crystalline-electric-field splitting on the order of $E/k_{\mathrm{B}}=1\text{–}10\mathrm{K}$. 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 $\approx 6\text{–}10\times {10}^{-5}\AA$, no structural phase transition occurs between $T=1.5$ and $50\mathrm{K}$. In combination with results from dilatometry measurements, we further show that the compound's thermal expansion has a minimum at $\approx 18\mathrm{K}$ and a region of negative thermal expansion for $9\lesssim T\lesssim 18\mathrm{K}$. Despite diffraction patterns taken at $1.6\mathrm{K}$ 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 ${\mathrm{Yb}}^{3+}$ residing on a site with either cubic or less than cubic point symmetry.

• Received 31 August 2015

DOI:https://doi.org/10.1103/PhysRevB.92.184111