Structural transformation in Tb_0.1Y_0.9Cu

A large anomaly has been observed in the thermal expansion of the intermetallic compound Tb_0.1Y_0.9Cu at 120 K. This anomaly has been attributed to a martensitic structural transformation and has all the characteristic effects of a large shape memory. Complementary neutron diffraction measurements have been performed over a large Q range at temperatures from 293 to 1.5K on diffractometers at both pulsed and steady state neutron sources. A complex structural phase transition is found to occur at the temperature where the anomaly in the thermal expansion takes place. A relevant feature of the phase transition is that it is not present in powder material. The cubic B2 (CsCl) structure is found to persist down to the onset of the structural transition. At and below the transition the transformed phase co-exists with the cubic crystallographic phase and is found to propagate throughout the crystal. The diffraction peaks at low temperatures display significant line broadening.