Pure and mixed rare-earth hydroxides are expected to be new materials for chemical heat pumps. In this study, the dehydration and hydration behavior of these materials was investigated by thermogravimetry. The dehydration temperature could be lowered by increasing the Nd or Gd ion content in the hydroxides. La0.50Gd0.50(OH)(3) is an ideal candidate material for chemical heat pumps that can store thermal energy at 300 degrees C; further, heat output can be generated from the heat source at 40 degrees C.