Comments on "Growth, XRD, optical, thermal, mechanical, electrical and NLO studies on mixture of potassium hydrogen phthalate and L-tartaric acid crystal for NLO applications"

Abstract

The authors of the title paper (Appl Phys A 127 496 (2021)) claim to have synthesized a "mixture of potassium hydrogen phthalate and L-tartaric acid" crystal by a slow evaporation of an aqueous solution containing equimolar amounts of potassium hydrogen phthalate (KHP) and L-tartaric acid. In this comment, many points of criticism, concerning the synthesis of the title crystal and its characterization, are highlighted to show that a so-called "mixture of potassium hydrogen phthalate and L-tartaric acid" crystal is, in fact, potassium hydrogen phthalate, (C sub(8)H sub(5)O sub(4)K). Due to no chemical reaction between KHP and L-tartaric acid in aqueous solution, fractional crystallization of the less soluble KHP occurs.