Mechanical Properties of Potassium Dihydrogen Phosphate Single Crystal by the Nanoindentation Technique

Abstract

Mechanical properties of potassium dihydrogen phosphate single crystal (KH₂PO₄, KDP) at room temperature were investigated using nanoindentation approaches. This study was carried out for two crystallographic planes of KDP single crystal, (001) crystallographic plane and the tripler crystallographic plane. The hardness and the reduced modulus values were calculated by the most commonly used Oliver–Pharr method. It was found that hardness and reduced modulus exhibited significant peak load dependence. Furthermore, the strong anisotropy of the hardness and reduced modulus were observed on two tested surfaces. At the same time, the indentation anisotropy of hardness and reduced modulus on each crystallographic face along different directions were estimated in detail. The results showed that these two faces behave quite differently from each other. The variations of hardness and reduced modulus values for (001) face and the tripler face both were periodic due to the rotational symmetry of crystallographic face microstructure and the indenter shape, and the periods were 90 and 120 degrees, respectively.

Keywords:

• Anisotropy
• Crystallographic face
• Crystallographic orientation
• Indentation size effect
• KDP single crystal
• Nanohardness
• Nanoindentation
• Reduced modulus

ACKNOWLEDGMENTS

The authors appreciate the financial support from the Key Project of National Natural Science Foundation of China (grant no. 50535020). We thank the State Key Lab of Crystal Materials, Shandong University, P.R. China, for the providing of the KH₂PO₄ crystal materials in this study.