Influence of Nb⁵⁺ ions on phase transitions and polar disorder above T_C in PbZrO₃ studied by Raman spectroscopy

Abstract

Micro‐Raman light scattering experiments on PbZrO3 (PZO) single crystal doped with Nb5+ have been investigated. Special attention was paid to the paraelectric (PE) phase in which nominally forbidden first‐order Raman spectra were detected at temperatures far above the phase transition TC. Complex Raman spectra were observed in the vicinity of three structural phase transitions. These results mainly from the coexistence of phases with different symmetries in a wide temperature range below TC. The Raman measurements have been compared with dielectric and optical observations and proved that polar nanoregions in a centrosymmetric lattice appear well above TC. It was shown that doping ABO3 perovskites with heterovalent ions like Nb5+ unbalances charge neutrality of the lattice and strongly extends the temperature range of polar regions. The investigations performed point out that in the PE matrix the interaction between electrons and lattice vibrations, as recently suggested for pure PZO, plays an important role.

Long-Term Isothermal Phase Transformation in Lead Zirconate

“…Therefore, the existence of two intermediate phases and the co-existence of phases have been proven. Similar behaviour was noted in previously investigated PZO crystals doped with Nb [21,23]. Because of the substantial temperature hysteresis of phase transitions observed in these crystals [20,21], we have decided to examine the time stability of the first intermediate phase (IM1).…”

“…Moreover, another phenomenon may play an essential role in relaxation processes in the phase of co-existing antiferroelectric and ferroelectric states. This is the flexoelectricity, manifesting by a sharp flexo-coupling peak at the T C of PZO [23]. Therefore, all that mentioned above points to the non-trivial co-existence of metastable states below T C in this material.…”

“…This choice was made because the temperature dependence of Raman light scattering for this crystal was carefully investigated and reported in ref. [23]. The measurement procedure of Raman light scattering in time was the same as that applied to the dielectric and pyroelectric current measurements described above.…”

“…Therefore, doping (or admixtures) and intentionally defected crystal [10] extends the temperature range in which the intermediate phase develops. Moreover, the PZO crystal doped with heterovalent ions, such as niobium [17][18][19][20][21][22], causes the appearance of a second intermediate phase, not observed before [21][22][23]. In addition, a substantial temperature hysteresis of phase existence was observed in that crystal [20,21].…”

Phase Transitions and Local Polarity above TC in a PbZr0.87Ti0.13O3 Single Crystal

“…In the investigated crystal, the P S is the order parameter, therefore, the presence of birefringence above T C indicates once again that the phase is polar. It is worth mentioning that polar nano-regions in a macroscopically centrosymmetric lattice appear well above T C in other oxide perovskites, such as BaTiO 3 , SrTiO 3 , PbTiO 3 or PbZrO 3 :Nb (e.g., [22][23][24]26,32]).…”