Study of ferroelectric‐antiferroelectric phase coexistence in
L
a‐doped
PZT
ceramics
Authors: Neagu Alexandra , Ciuchi Ioana Veronica , Mitoseriu Liliana , Galassi Carmen , Tai Cheuk‐Wai 
Published: December 2016

Due to their wide applications in microelectromechanical systems and energy storage devices lead zirconate titanate–based antiferroelectrics have a significant technological and commercial importance
1,2
. It has been already established that in the PbZrO
3
–PbTiO
3
(PZT) solid solution at the Zr‐rich end of the phase diagram, an antiferroelectric/ferroelectric (AFE/FE) phase boundary exists
3
. At this phase boundary, switching from the AFE to the FE state using an applied field or stress induces large effective strains or charges. In order to broaden the phase transition and reduce the free energy difference between the AFE and FE phases these Zr‐rich PZT solid solutions are often doped with La, Nb or Sn. Generally doping with La was found to increase the stability range of the antiferroelectric orthorhombic phase. Moreover previous studies have shown that there is a region of coexistence of the AFE/FE phases for La‐doped PZT where their functional properties are improved
4
.

In this study Transmission Electron Microscopy (TEM) was employed in order to investigate in detail the AFE/FE phase coexistence region for a number of Pb
1‐x
La
x
(Zr
0.9
Ti
0.1
)
1‐x/4
O
3
(PLZT x/90/10) compositions prepared with the mixed oxide solid state reaction method, with
x
=0.025, 0.030, 0.032, 0.033, 0.035, 0.040. Previous studies
5,6
based on XRD and anelastic and dielectric spectroscopy measurements have suggested for 0 ≤
x
< 0.020 a rhombohedral FE phase, for 0.025 ≤
x
< 0.035 a phase coexistence region of orthorhombic and rhombohedral phases and for
x
≥ 0.035 an orthorhombic AFE phase. The TEM study revealed that all investigated compositions contained grains that in the SAED patterns showed satellite spots along <110>
pc
directions with a periodicity of 8‐9 (110) spacings. These satellite spots are associated with a long‐period ordered incommensurate antiferroelectric structure. The incommensurate modulations spots along the <110>
pc
shown in the SADPs can be expressed as ha* + kb* + lc* ± 1/n(a*+ b*). For lower La‐content (
x
=0.025, 0.030) also grains that do not contain the incommensurate antiferroelectric phase at all have been found suggesting chemical inhomogeneity. On the other hand, for higher La‐content (
x
> 0.030) all investigated grains presented the incommensurate modulated spots. For these compositions most grains presented a multi‐domain configuration with alternating AFE‐FE domains as shown in Fig. 1(a). Domains denoted with odd numbers (1, 3, 5) are AFE while domains denoted with even numbers (2, 4) are FE. The presence of satellites spots in the DP pattern of AFE domains is always accompanied by the presence of stripes in the BF and DF images, perpendicular to the direction of the spots as seen in Fig. 1(b) and (c). Based on these results for the investigated samples, La‐dopant impurities may only induce a competition between the antiferroelectric and ferroelectric ordering due to the disruption of long‐range dipolar interactions.