UC Irvine

Ce3Bi4Pt3 is a cerium compound that exhibits a hybridization gap and concomitant semiconducting behavior in the coherent ground state. Using neutron powder diffraction, we have determined the variation of the lattice constant with temperature at two pressures (P=10-3 and 17.7 kbar), and determined the bulk modulus and atomic mean-square displacements for Ce3Bi4Pt3 and its normal analog, La3Bi4Pt3. The thermal expansion Δβ in Ce3Bi4Pt3 exhibits a maximum at Tmax=50 K at ambient pressure. Below 50 K, the bulk modulus ΔB is proportional to TΔβ. We apply a Grüneisen analysis, under the assumption that the free energy exhibits T/T0(V) scaling. The Grüneisen parameter deduced from the ratio ΔB/TΔβ is consistent with the value Ω=36 deduced from the pressure variation of Tmax. The analysis allows us to predict the temperature dependence of the 4f specific heat (ΔCΔβ/Ω), which thus has a maximum at 50 K and a high-temperature entropy nearly equal the expected value R ln6. We argue that the maximum at 50 K reflects an (indirect) hybridization gap of order 100 K. We show further that the lattice constant anomaly Δa0 is proportional to the effective moment Tχ; this suggests that a relationship known to be valid for antiferromagnets, namely (Tχ)/TΔC where ΔC is the specific heat, may be valid for Ce3Bi4Pt3. Finally, we show that the temperature dependence of the mean-square atomic displacements is nearly identical for Ce3Bi4Pt3 and La3Bi4Pt3 and can be fitted by a simple Debye-Waller model; hence the expansion anomaly does not affect the average lattice dynamics. © 1992 The American Physical Society.