The temperature dependence of the external modes not containing any significant lithium ion contribution were also investigated in LiNaSO(, 4), LiKSO(, 4), and NaK(, 3)(SO(, 4))(, 2). Modes containing sulfate ion rotational motion were found to be very temperature sensitive and were discussed in terms of their role in the phase transitions.

Raman and infrared reflection spectra were used to assign internal and external modes in LiNaSO(, 4), LiKSO(, 4), and NaK(, 3)(SO(, 4))(, 2). Temperature-dependent Raman studies were performed on these vibrational modes.

Modes due predominately to lithium ion motion in LiKSO(, 4) and LiNaSO(, 4) were identified through measurements in isotopically enriched (('6)Li) crystals and were studied in detail. Activation energies for lithium ion motion were calculated from the measured temperature dependence of the frequencies and bandwidths of the lithium ion modes.

Internal mode temperature dependent Raman studies provided information concerning the sulfate sublattice as it undergoes the phase transition in the three sulfate systems.