Mechanism of the ferroelectric phase transitions in LiNbO3 and LiTaO3 -: art. no. 052107

The temperature dependences of the nuclear-electric-quadrupole frequency omega(Q) of In-117 doped in LiTaO3 (T-C = 938 K) and Li1-xInx/3TaO3 with x = 0.2 (T-C = 818 K) show that the order-disorder of the Li ions is not the driving mechanism for the ferroelectric instability in LiNbO3 and LiTaO3 systems, and imply that the oxygen order-disorder is the driving mechanism. The significantly different temperature dependences of omega(Q) of Cd-111 in these materials compared, to those of In-117, demonstrate that this order-disorder is of dynamic character.