The structural paths of the phase transitions in ferroelectrics: high-resolution single crystal X-ray diffraction study
2CHEMISTRY, Simon Fraser University, Burnaby, British Colombia, Canada
(1-x)Pb(Mn1/3Nb2/3)O3-xPbTiO3 (PMN-PT) is a ferroelectric material with many uses [1]. Due to its perovskite-type structure, PMN-PT forms ferroic domains patterns during phase transitions. These domains are the source for PMN-PT functionality. Additionally, the phase transitions are governed by the composition of PMN-PT (x) and temperature (T). The phase transition between the para- and ferroelectric phases has been extensively studied. However, all the existing x-T phase diagrams are reconstructed with rough temperature steps, and an actual mechanism of the phase transition is still poorly understood. Understanding the phase transition mechanism in PMN-PT may shed light on unclear phase transition mechanisms in other materials.
This work aims to improve the understanding of phase transitions in PMN-PT, using high-resolution single crystal X-ray diffraction. We conducted the experiments at a custom-made diffractometer at Tel-Aviv University [2], and ID28@ESRF beamline. We measured PMN-29.5PT and PMN-35PT single crystals, while gradually changing the temperature (ΔT=0.1~1ºC). We collected series of 3D Reciprocal Space Volumes, representing the diffraction intensity around certain Bragg peaks. Due to the formation of domains, these Bragg peaks split into components [3]. Through preliminary analysis, we managed to find a new intermediate state between the tetragonal and the cubic phases, which corresponds to a monoclinic phase. This state ranges from 163 to 167ºC for PMN-35PT. Our results point to a mechanism of phase transition from the tetragonal phase to the intermediate state, via a habit plane, and then, similarly, to a cubic phase.
[1] Park S. E. & Shrout T. R. (1997). J. App. Phys., 82, 1804-1811
[2] Gorfman S., Spirito D., Cohen N., Siffalovic P., Nadazdy P., Li Y. (2021). J. Appl. Cryst., 54, 914-923.
[3] Gorfman S., Spirito D., Zhang G., Detlefs C., Zhang N. (2022) Acta. Cryst. A., 78, 158-171.
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