Revisiting phonons and the phase transition sequence in antiferroelectric Pb_0.98La_0.02(Zr_0.95Ti_0.05)O₃

Abstract The changes induced in Pb 0.98 La 0.02 (Zr 0.95 Ti 0.05 )O 3 (PLZT 2/95/5) by 2% of La substitution and its impact on the phase transition sequence were investigated by using Raman spectroscopy, differential scanning calorimetry, and x-ray diffraction to improve the understanding of the switching dynamics of antiferroelectric-ferroelectric systems. Comparison with Pb(Zr 0.95 Ti 0.05 )O 3 confirms that the La substitution alters the Pb dynamics and suppresses the polar order, stabilising the antipolar state already at high temperatures. On cooling from the cubic paraelectric phase, the calorimetric data revealed a small anomaly near T ’∼500 K corresponding to a region where the material appears macroscopically cubic, but it is locally distorted. Then an antiferroelectric incommensurate phase appears below T C ∼ 483 K, characterised by new Raman modes and three main soft modes: an antiferrodistortive soft mode, an antipolar soft mode, and a weaker soft mode at very low frequencies, related to the incommensurate positions of Pb, the amplitudon, which disappears when the material enters another antiferroelectric phase. The average symmetry of the intermediate incommensurate antiferroelectric phase is likely orthorhombic with the proposed Imma space group. The low temperature antiferroelectric phase shares the same space group ( Pbam ) and Raman modes with antiferroelectric PZT ceramics. Based on this combined approach, the proposed phase transition sequence on cooling is cubic paraelectric–cubic distorted paraelectric–incommensurate antiferroelectric Imma –orthorhombic antiferroelectric Pbam .