Broadband gigahertz dynamics of relaxor ferroelectric Pb(Sc1/2Nb1/2)O3-xPbTiO3 single crystal probed by Brillouin scattering

Abstract

The broadband gigahertz dynamics of a relaxor ferroelectric crystal 0.70Pb(Sc 1/2 Nb 1/2 )O 3 -0.30PbTiO 3 with a composition close to the starting point of the morphotropic phase boundary is studied by Brillouin scattering. The significant anomaly of the longitudinal acoustic (LA) mode is observed in the vicinity of the Curie temperature, T C ¼ 500 K. Upon cooling, it starts below the Burns temperature, T B ¼ 670 K, due to the interaction between the LA mode and dynamic polar nanoregions (PNRs). The broad central peak (CP) clearly appears below T B , and its intensity becomes a maximum at T C . The relaxation time, s CP , determined from the CP width, shows the typical critical slowing down of the order-disorder phase transition in the vicinity of T C . The size of a dynamic PNR significantly increases below the intermediate temperature, T* ¼ 562 K.

Role of dynamic polar nanoregions in heterovalent perovskite relaxor: Inelastic light scattering study of ferroelectric Ti rich Pb(Zn1/3Nb2/3)O3-PbTiO3

“…In both heating and cooling processes, a significant softening of the LA mode and a clear anomaly corresponding to the cubic-tetragonal phase transition are observed at 481 K (T C-T ), which can be attributed to the interaction between the LA mode and the polarization flipping inside the dynamic PNRs. 16 The observed anomalous temperature dependence is similar to that of PMN-55PT with no COR, 15,28 while such a sharp elastic anomaly is uncharacteristic in typical RFEs such as PMN, PZN with CORs. In addition, LA shows a mild softening below T B $ 700 K, demonstrating that only normal anharmonic effects dominate in the lattice dynamics above T B .…”

“…The value of s 1 is comparable with that of 0.70Pb(Sc 1/2 Nb 1/2 )O 3 -0.30PbTiO 3 (PSN-30PT), while the value of s 0 is much smaller than that of PSN-30PT reflecting the first-order nature of the ferroelectric phase transition in PZN-15PT. 16 The observed critical slowing down is characteristic of an order-disorder phase transition. In PZN-7PT, slowing down was observed; however, the critical slowing down is suppressed near T C due to the existence of CORs.…”

“…16,32 Figure 5 shows the temperature dependence of l PNR for PZN-15PT between T B $ 700 K and T * $ 600 K. At high temperatures, the size of dynamic PNRs is about 3 nm and remains nearly constant, while upon cooling below T * starts to increase sharply and reaches 13 nm near T C-T on cooling. These values are comparable with those of PZN-4.5PT determined by neutron diffuse scattering and the initial size of dynamic PNRs of $2.5 nm in PZN-7PT at T * determined by Brillouin scattering.…”

“…The temperature dependence of C LA , which is related to the acoustic damping of the LA mode, shows the sharp increase near T C-T , suggesting the increase of scattering of the LA mode by the growth of dynamic PNRs. 15,16 …”

“…Therefore, the temperature dependence of the local polarization fluctuations of PNRs can be detected with a high sensitivity by the broadband Brillouin scattering technique in the frequency range from 1 to 1000 GHz. 16 Up to the present, Brillouin scattering studies have been performed on PZN 17,18 and the PZN-xPT solid solutions, i.e., PZN-4.5PT crystals, 9,19 PZN-7PT, 20,21 PZN-9PT, [22][23][24] and PZN-20PT. 25 The compositions with PT content smaller than x ¼ 0.09 exhibit relaxor behavior with a diffuse and dispersive permittivity maximum and transforms the relaxor state into a stable ferroelectric phase with rhombohedral symmetry at low temperatures.…”