Lanthanide hexaborides. I. Heat capacities and some thermophysical properties of LaB 6, NdB6 , and GdB 6at temperatures from 5 K to 350 K

Abstract Heat-capacity measurements made on zone-refined rods of LaB 6 , NdB 6 , and GdB 6 revealed no anomalies in diamagnetic LaB 6 , but paramagnetic NdB 6 showed a cooperative λ -type transition associated with antiferromagnetic ordering near T  /  K  =  (8.4  ±  0.2) with Δ trs S o  /  R  =  (1.39  ±  0.06) and a GdB 6 a similar appearing λ -transition at T  /  K  =  (15.7  ±  0.3) and Δ trs S o  /  R  =  (2.08  ±  0.04). The heat capacity ( C p  /  R ), entropy { S o ( T )  −  S o (0) /  R }, and Gibbs energy { G o ( T )  −  H o (0)} /  RT for LaB 6 are (11.66  ±  0.03), (9.999  ±  0.03), and (4.376  ±  0.03) at T  =  298.15 K. Corresponding values for NdB 6 are 11.92, 12.445, 6.335 and for GdB 6 are 15.98, 13.274, and 8.955.