Characterization and criteria of phase transformations and lattice slipping in potassium dihydrogen phosphate crystals

Abstract

Potassium dihydrogen phosphate (KDP) is an important nonlinear optical material. Since the 1930s, this material has attracted significant attention because of its excellent physical and optical properties. [1][2][3][4] KDP has been widely used in many technological fields, such as laser frequency conversion, high-speed Q-switching, optical communication, and optical signal processing. [5][6][7][8][9] At the present, one can easily obtain a large aperture KDP with the rapid growth technology. 10,11 To use a KDP component in high-energy laser systems [12][13][14][15] ; however, it is required to minimize the surface and subsurface damages which are mostly introduced in a mechanical surface finishing process. An ideal outcome is that the manufactured KDP component is totally damage free. However, KDP is one of the most difficult-to-handle materials due to its fragility, unstable microstructure, and complicated mechanical behavior. 16,17 A low-quality surface or subsurface can easily reduce the laser-damage threshold (LDT) and the service life of a KDP component. 18,19 How to overcome the difficulties and improve the machinability of KDP has been challenging.There are many issues in relation to the damage-free manufacture of a KDP component, among which the most critical is its complicated deformation mechanisms under external loading. At stressing, a KDP crystal can undergo

Effect of Anisotropy of Potassium Dihydrogen Phosphate Crystals on Its Deformation Mechanisms Subjected to Nanoindentation

“…An effective characterization method is important for identifying structural changes in a material − but is unavailable for KDP, probably due to its complex microstructure . To facilitate the KDP characterization process, Yang et al carried out a characterization method based on two judgment criteria, which can effectively identify the structural changes in KDP.…”

“…An effective characterization method is important for identifying structural changes in a material − but is unavailable for KDP, probably due to its complex microstructure . To facilitate the KDP characterization process, Yang et al carried out a characterization method based on two judgment criteria, which can effectively identify the structural changes in KDP. However, similar to that in the Common Neighbor Analysis (CNA) and the Common Neighborhood Parameter (CNP), the characterization method requires user-specified thresholds, which is very complicated for KDP due to its complex microstructure.…”

“…Figure shows a P–O–H–O–P chain in a KDP crystal in which the angle between the vector P 1 O 1 and vector P 2 O 2 represents the vector angle of every H-bond. The H-bonds and their adjacent PO 4 groups in different environments are proved to be accurately identified by this criterion A1 Specific P–O–H–O–P chain in a KDP crystal …”

“…The H-bonds and their adjacent PO 4 groups in different environments are proved to be accurately identified by this criterion A1 Specific P–O–H–O–P chain in a KDP crystal To improve the accuracy of the machine learning-based method, another popular characterization parameter named torsion angle, which is usually used to identify different protein molecules, , is involved.…”

“…In this criterion, the nearest O atoms within a cutoff of 3.85 Å are defined as the neighbor O atoms and are counted. The numbers of P atoms with a distance less than 1.8 Å between themselves and the O atoms are counted as the donor PO 4 groups.

A2 Coordination of K cations (K–O distances in Å)

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