Raman Scattering Study of ND₄⁺ -Ion Motion and Structural Phase Transitions in ( ND₄)₂PbCl₆

Raman spectra of the internal modes of ND₄⁺-Ion in ( ND₄)₂PbCl₆ crystal have been recorded in the temperature range of 5 - 300K. A new structural phase transition was observed at 34 K because of deuterium effect. Discontinuous behaviours of the interna1 modes of the ND₄⁺-ion at this temperature show that the structural transition is one of first order.