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.