Deformation behavior of PZN–6%PT single crystal during nanoindentation

Abstract

The deformation behavior of [001]^T- and [011]^T-cut single crystal solid solution of Pb(Zn_1/3Nb_2/3)O₃–6% PbTiO₃ (PZN–6%PT) in both unpoled and poled states has been investigated by nanoindentation. Nanoindentation experiments reveal that material pile-up and local damage around the indentation impressions are observed at ultra-low loads. These pile-ups and local damage cause a pop-in event (i.e. a sudden increase in displacement at an approximately constant load) in the nanoindentation load–displacement curve (P–h curve). Detailed studies of the relationships between indentation load (P), displacement (h) and harmonic contact stiffness (S) suggest that there is a surface layer, possibly due to crystal fabrication processes, which possesses different mechanical properties from the interior. The thickness of this surface layer is estimated to be approximately 300 nm. Furthermore, it is found that [011]^T-cut crystal is stiffer than [001]^T-cut crystal. On the other hand, both [001]^T- and [011]^T-cut crystals in unpoled state possess lower contact stiffness than poled crystals. This finding suggests that poling improved the mechanical property of the crystal. In summary, poled [001]^T-cut crystals have an elastic modulus of (107 ± 6) GPa and a hardness of (5.1 ± 0.4) GPa. In contrast, the modulus for [011]^T-cut crystals is not constant but increases with indentation depth.

Keywords:

• nanoindentation
• PZN-PT
• relaxor-based single crystal
• piezoelectric
• deformation

Acknowledgements

The authors thank Microfine Technologies Pte Ltd (Singapore) for providing samples of PZN–PT for this work. The support by Lu Shen from Institute of Materials Research and Engineering (Singapore) during the nanoindentation experiments is greatly appreciated. Thanks also to Professor L.C. Lim from Department of Mechanical Engineering, NUS and Dr K.K. Rajan from Microfine Technologies Pte Ltd (Singapore) for valuable discussions and suggestions. This work is financially supported by Ministry of Education, Singapore through National University of Singapore under Academic Research Funding R-265-000-257-112.