Powder X‐Ray Diffraction Technique: Unknown Facts About the True Degree of Crystalline Perfection of Bulk Single Crystals

ABSTRACT From the standpoint of crystal growth and characterization, there persists a widespread misconception that optically transparent crystals inherently possess a high degree of crystalline perfection. Many researchers in this field maintain that if the powder X‐ray diffraction (XRD) pattern of a grown crystal exhibits sharp, high‐intensity reflections, it unequivocally indicates a superior level of crystalline perfection. Indeed, it may not be a technically correct method to identify the degree of crystalline perfection since it cannot always provide the true degree of crystalline nature of a grown crystal. In this article, we demonstrate the manner by which the realization of crystalline perfection of the optically transparent crystals in the form of single crystals can be a reality, while their respective polycrystalline counterparts (powder form of the single crystals) may not be. This is an attempt to provide a reliable substantiation for the above‐mentioned statements with proven examples of technologically important single crystals for which systematic X‐ray diffraction studies have been made. Based on the diffraction results obtained, we ascertain that the XRD data of cut and polished single crystals provide a far more reliable and authentic assessment of their crystalline perfection than their corresponding powder forms.