Peculiarities of the Structure, Moduli of Elasticity, and Knoop Indentation Patterns of Deformation and Fracture of Single Crystals of Potassium, Rubidium, Cesium, and Ammonium Hydrophthalates

The crystal structure of potassium, rubidium, cesium, and ammonium hydrophthalates is analyzed based on the data in the literature. A relationship between their structure and elastic and mechanical properties has been established for the first time. Young's moduli, shear moduli, and Poisson's ratios in the (100), (010), and (001) planes of these crystals are calculated, and Knoop indentation of these planes is performed. Anisotropy of the elastic and mechanical properties of the crystals is revealed. Rubidium, cesium, and ammonium hydrophthalates are found to be partial auxetics. Ammonium hydrophthalate, whose structure contains additional (as compared with other hydrophthalates) hydrogen bonds, exhibits the highest anisotropy of properties.