Light-Scattering Studies of the Soft Ferroelectric and Acoustic Modes of KD2PO4

Brillouin scattering studies of acoustic phonon modes and central peak in single-crystal Pb(Sc1/2Ta1/2)OSivasubramanian1, Kojima2 2012Phys. Rev. B

“…The best fit of the experimental data yields τ * = 2.3 ps and τ 2 = 7.7 ps. The value of τ * is similar to that reported for KD 2 PO 4 (1.3 ps for T > T c ) 30 which exhibits order-disorder behavior in the vicinity of the transition temperature. A similar value is reported for disordered Pb(Sc 1/2 Nb 1/2 )O 3 (PSN) in the cubic phase (5 ps).…”

Direct evidence of an order-disorder nature of ferroelectric phase transitions in K2MgWO2(PO4)2

“…For instance, in the ferroelectric phases of PbHPO 4 , triglycine sulfate, and nearly stoichiometric LiTaO 3 , 0 were found to be 0.04, 0.096, and 0.014 ps, respectively. [22][23][24] Similar time as for KMWP was found, however, for KD 2 PO 4 ͑1.3 ps in the piezoelectric tetragonal phase 21 ͒, which is known to exhibit a phase transition of both order-disorder and displacive types. 25 Our results show that the relaxation mode relates to E-symmetry excitation in the tetragonal phase and it involves ionic motions within the plane perpendicular to the tetragonal z axis.…”

“…The presence of such interference dip is a direct indication that a coupling exists between CP and the acoustic mode. 21,28 In the monoclinic phase, the signal can be observed for light propagating along the polar axis ͑in one type of domains͒ or perpendicularly to the polar axis ͑second type of domains͒. In the first case, the two transverse modes are forbidden.…”

“…19 When, however, the transition occurs between two piezoelectric phases, the transition is of the first order or coupling between a relaxation and other mode exists, incomplete softening of the relaxation mode should be observed. [19][20][21] Since our spectra give indication of a coupling between the relaxation and acoustic modes ͑see discussion below͒, and all phases of KMWP are piezoelectric, it is not surprising that the observed relaxation modes exhibit incomplete softening. The temperature dependence of the relaxation time shows that the transition at T 2 is strongly first order.…”

High-resolution temperature-dependent Brillouin scattering studies of ferroelectricK3Nb3O6(BMączka1, Hanuza2, Kojima3 2008Phys. Rev. B

“…For example, for the tetragonal phases of KD 2 PO 4 and K 2 MgWO 2 ͑PO 4 ͒ 2 , 0 are 1.3 and 3.8 ps, respectively. 42,43 In case of KNBO, the long relaxation time can be most likely attributed to coupling between the relaxation modes related to the polarization and pseudospindensity fluctuations. It is also worth noting that the ratio of 0 in the phase stable above T 4 to 0 in the phase stable below T 4 is close to 2 ͑2.09͒, which shows that the phase transition at T 4 should be close to a second order one.…”