The cubic-tetragonal tranformation in metal decarbides-II Lanthanide dicarbides and some mixed lanthanide dicarbide solid solutions

The cubic → tetragonal phase transition temperatures of arc-melted beads of all the lanthanide dicarbides except SmC₂, TbC₂ and TmC₂ have been determined. The effect of inter-solution of the dicarbides on the transformation temperature T_τ has been studied for twenty-six pairs and a relationship established between depression of T_τ and the difference in unit cell volumes ΔV of the dicarbides. For dissolution of larger cell volume dicarbides into dicarbides of smaller cell volume, ΔT_τ=K(ΔV)². No such simple relationship exists for the reverse process, which suggests that lattice strain energy is the dominant effect in determining T_τ for mixed dicarbides. Why ΔT_τ can be used to indicate lattice strain is shown and the nature of this type of transformation is discussed.