M A T E R I A L S F O R T O M O R R O W ' S I N N O V A T I V E A N D S U S T A I N A B L E I N D U S T R Y

S C I E N T I F I C H I G H L I G H T S

5 6 H I G H L I G H T S 2 0 2 3 I

X-ray diffraction reveals texture in lead zirconate titanate piezoceramics

X-ray diffraction was used to probe texture and strain in a range of newly developed lead zirconate titanate [Pb(Zr, Ti)O3] or PZT-based textured ceramics with both high electromechanical properties and good thermal stability, resolving the dilemma that piezoelectricity and Curie temperature can only be enhanced at the expense of each other.

PZT-based ceramics are the materials of choice for numerous electromechanical devices, such as high- precision actuators, ultrasonic medical transducers and mechanical energy harvesters. Because the piezoelectricity determines the key parameters (e.g., sensitivity and resolution) of electromechanical devices, further enhancing the piezoelectric properties of PZT ceramics is of great importance for developing next- generation electromechanical devices. Tailoring ceramic grains along a specific crystallographic orientation allows the utilisation of inherent property anisotropy, providing an effective way to further enhance the piezoelectricity of PZTs. However, because of the serious reaction between PZT powder and commonly used titanate templates (BaTiO3 and SrTiO3) during sintering, the progress in manufacturing textured PZT ceramics has been very slow since the 1990s.

In 2023, a seed-passivated texturing process was proposed to resolve this challenge. First, novel barium zirconate titanate [Ba(Zr, Ti)O3, BZT] templates were developed to replace the conventional titanate ones, which improves the template stability in the PZT matrix. Second, two different layers were prepared via tape casting (i.e., a mixture of BZT templates and PZT matrix powder with lower PZ content) and pure PZ powder (Figure 39a). The two different layers were alternately stacked to form the final green sample, which guarantees the template-induced grain growth in the Zr-deficient layer while achieving the desired composition through ion diffusions between the different layers during sintering. For the first time, highly <001>-textured PZT ceramics with PZ content up to 70% were successfully created. In particular, significantly enhanced piezoelectric properties (piezoelectric coefficient d33~760 pC/N, g33~100 mV m/N, electromechanical coupling coefficient k33~0.85, and strain ~0.57% at 50 kV/cm) and good temperature stability (Curie temperature ~360°C) are achieved in the textured PZT ceramics with the composition near the morphotropic phase boundary (Figure 39b-d), which resolves the dilemma that the piezoelectricity and Curie temperature can only be enhanced at the expense of each other.

High-energy X-ray diffraction (XRD) was used at beamline ID15A to perform texture and strain analysis experiments. First, the {200} pole figure of Pb(Zr0.55Ti0.45)O3 ceramic

Fig. 39: a) Schematic illustration of the proposed texturing process. The colour of the PZT matrix indicates its composition. b) The d33 and (c) k33 as a function of Curie temperature for both PZT-based textured ceramics and representative state-of-the-art

piezoelectric ceramics. d) A comparison of the electric field-induced strains between the textured Pb(Zr0.55Ti0.45)O3 ceramic, <001>-oriented PMN-27PT single crystal, and commercial PZT-5 ceramic.