Origin of pinched hysteresis in PbZrO3-PbTiO3-PbHfO3 and its restoration to typical ferroelectric hysteresis

Abstract Ferroelectric materials typically exhibit single-loop hysteresis with substantial remnant polarization, while the anti-ferroelectric materials show double-loop hysteresis with zero remnant polarization. Some polar materials exhibit a deformed loop or double loops with very low (non-zero) remnant polarization. These deformed loops are termed as pinched or constricted hysteresis loops. The origin of the pinched loop is mostly attributed to charged point defects and some of these are associated mainly with oxygen (or other elements like Pb, Bi, etc.) vacancies. The present study explores the origin of pinched loops in Pb(Zr,Ti,Hf)O 3 ceramics. The introduction of Hf in Pb(Zr,Ti)O 3 causes pinching even though the replacement of Zr/Ti with Hf does not create an extra charge imbalance. Further, the degree of pinching is regulated without changing the charge state as the Hf-content is varied while the Zr/Ti ratio is kept unchanged. Strong frequency dependence is observed and the change in lattice vibration is found to be associated with the pinched nature. The change in electronic band structure is observed through photoluminescence and reflectance spectroscopy. These observations suggest the presence of defects in these materials. However, these defects are non-charged in nature, which hindered the switching and thereby caused the pinching. The pinching is caused by octahedral tilting originating from the mass and size difference between Hf and Zr/Ti. The tilting is reverted back by the chemical influence of La induction and successfully restores the typical ferroelectric hysteresis loop.