On the optimum processing conditions of Pb(Zr_xTi_1−x)O₃: revealing the mechanisms to increase the piezoelectric coefficients up to 1100 pm V⁻¹

Abstract

The ferroelectric compound family Pb(Zr x Ti1−x )O3 (PZT) is one of the most investigated and widely used piezoelectric materials. Optimization of the piezoelectric coefficients is observed for x ~ 0.52 (Pb(Zr0.52Ti0.48)O3) and is further promoted by the increase of grain size (GS). However, in some cases the piezoelectric properties of Pb(Zr0.52Ti0.48)O3 deteriorate upon processing due to the decrease of density, ρ, that is mostly ascribed to the appearance of byproduct phases. In the present study we discuss the influence of the processing conditions on the piezoelectric properties for polycrystalline Pb(Zr0.52Ti0.48)O3, specifically focusing on the sintering temperature, 1100 °C ⩽ T sin ⩽ 1250 °C. To this end, we use atomic force microscopy (AFM), Archimedes’ method, x-ray diffraction (XRD) and a newly introduced local technique, based on a conventional optical microscope, which is further developed here to accommodate non-clamped specimens. The data obtained via this technique in the regime of relatively high electric fields evidence that the absolute piezoelectric coefficients, |d zi | (i = x, y) show a non-monotonic behavior with an unexpectedly high maximum value |d zi | ~ 1100 pm V−1 at T sin = 1180 °C. These features are accompanied by a progressive increase of coercivity, reaching maximum value E C,i ~ 4.5–5.0 kV cm−1 (i = x, y) at T sin = 1250 °C. To explain these findings, the |d zi | coefficients are compared with the microstructure and compositional information, coming from AFM, Archimedes’ method and XRD data. We conclude that the significantly high |d zi | values observed for samples prepared at T sin = 1180 °C are motivated by the increase of mean GS, <GS>, while for T sin > 1180 °C the decrease of density, ρ, ascribed to the appearance of byproduct phases, dominates and deteriorates |d zi |. These experimental results on |d zi |(T sin) are reliably reproduced by a phenomenological model with reasonable assumptions for <GS> (T sin) and ρ(T sin). The unexpectedly high piezoelectric coefficients, |d zi | ~ 1100 pm V−1, reported here for the first time, are provocative and call for utilization of the introduced approach in the investigation of the respective properties of other compounds.

Pronounced and reversible modulation of the piezoelectric coefficients by a low magnetic field in a magnetoelectric PZT-5%Fe3O4 system

“…The raw data of panels (c.i) and (d.i) are accessible in ‘Section III’ of Supplementary Information and the accompanying Supplementary Videos. Please note that, as expected 37,38 , the respective S zx (E ex,z ) loops are practically horizontal lines, since the investigated area was onto SA y (see insets of Fig. 6(b.i–b.ii)).…”

“…The insets of the upper panels, (a.i) and (a.ii), show photos of the specific samples together with an arbitrarily chosen coordinate system that assists us to define the symmetry axes x (SA x ) and y (SA y ). As it should be, the investigated area was at the sample edge, in the specific case onto SA y , as shown with a white dot for both samples (for details see ‘Section III’ of Supplementary Information and 37,38 ). Concerning the experimental procedure, six consecutive E ex,z loops were recorded designated by a loop index; first, without the application of H ex,z (loop index: 1 and 2), next, under the presence of H ex,z = 1 kOe (loop index: 3 and 4) and finally, when removing H ex,z (loop index: 5 and 6).…”

“…The constitutive Strain-Electric field curve, S(E ex,z ), of samples PZT-5%Fe 3 O 4 was estimated experimentally by using an OM-based technique already discussed in 37,38 for out-of-plane E ex,z up to 10 kV/cm. Here, we made another modification in the home-made aluminum platform hosting the sample, so that a constant, also out-of-plane magnetic field, H ex,z , is applied at will, by a NdFeB permanent magnet, (disc-shaped with diameter 20 mm and thickness 3 mm).…”

“…Concerning the experimental procedure, six consecutive E ex,z loops were recorded designated by a loop index; first, without the application of H ex,z (loop index: 1 and 2), next, under the presence of H ex,z = 1 kOe (loop index: 3 and 4) and finally, when removing H ex,z (loop index: 5 and 6). Figure 6(a.i,a.ii) present the mean absolute value of the in-plane PE coefficient in the y-direction, <|d zy |>, for the complete sequence of measurements (the other in-plane PE coefficient in the x-direction, d zx , is not shown since it is obviously zero 37,38 ). Specifically, these panels present explicit data on < |d zy | > before applying (loop index: 1 and 2), upon application (loop index: 3 and 4) and after removal (loop index: 5 and 6) of a constant H ex,z = 1 kOe.…”

“…We focus on the variation of the in-plane PE coefficients upon application of an E ex,z (ranging within ± 10 kV/cm) and a relatively low H ex,z (1 kOe), that are both applied out-of-plane at room temperature. By means of a method based on optical microscopy 37,38 , we showed in a direct way that the application of such a low H ex = 1 kOe, causes a pronounced decrease of the in-plane PE coefficients on the order of 50–60%, that intriguingly is restored upon successive removal of H ex . Polarization data showed that with the addition of the Fe 3 O 4 NPs, PZT becomes harder when compared to its plain form.…”