IMF 2023

Mode coupling and improper ferrielectric phase transition in the PZT and PMN-PSN phase transitions/

Sergey Vakhrushev 1 Alexei Bossak 3 Yurii Bronwald 1 Dmitry Chernyshov 2 Igor Leontyev 4 Konstantin Petroukhno 1 Igor Raevski 4
1Neutron Research Laboratory, Ioffe Institute, Saint Petersburg, Russia
2CRG / BM01, Swiss-Norwegian Beamlines at ESRF, Grenoble, France
3EXP / EMD / ID28, European Synchrotron Radiation Facility, Grenoble, France
4Research Institute of Physics, Faculty of Physics, Southern Federal University, Rostov on Don, Russia

Some antiferroelectric/ferroelectric (AFE/FE) solid solutions, e.g. PbZr1-xTixO3 with x<0.06, undergo transition to the AFE state through the intermediate presumably FE phase (IP). On cooling to the IP the diffuse scattering (DS) near the (h+½ k+½ l) (M-point) in the (qq0) direction was reported. This scattering is extinct at h=k and has the asymmetric shape with the bump at one side of the M-point and the minimum at the other side. Such DS was first reported in pure PbZrO3 [1]. In the IP phase M-superstructure peaks arise without any extinction rules. It was demonstrated that when approaching the transition to the IF, a soft antiferrodistortive (AFD) oxygen mode occurs. Aside of the M-point this softening leads to the inevitable mode coupling between AFD and transverse acoustic modes, leading to the emergence of a mixed soft mode with eigenvectors that are a combination of lead and oxygen displacements [2]. Condensation of the ferroelectric and said mixed modes leads to the formation of a structure that includes the ferroelectric and antiferroelectric (characterized by the q=(½ ½ 0)) displacements of lead ions and can be described as a NON-COLLINEAR IMPROPER FERRIELECTRIC structure.

We studied also the DS in PMN0.65PSN0.35 solid solution. On cooling from 500K to 80K first the DS develops aside of (h+½ k+½ l) with h≠k points and the minima is observed at the (h+½ k+½ l) with h=k positions. Such extinction is typical for the oxygen M3 mode. On further cooling down superstructure peaks arise at all (h+½ k+½ l) positions implying that antiparallel cation displacements appear as well. So similar to the previous case we can address this as NON-COLLINEAR IMPROPER (since the driving force is oxygen mode) FERRIELECTRIC transition.

The study was supported by Russian Science Foundation grant №22-12-00328, https://rscf.ru/en/project/22-12-00328/.

[1] Pasciak, M. et al. Phase Transit. 2015, 88, 273–282

[2] Vakhrushev, S. et al. Materials 15 (2022) 79

The study was supported by Russian Science Foundation grant №22-12-00328, https://rscf.ru/en/project/22-12-00328/





IMF 2023




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