Inquiry-Based Experiment with Powder XRD and FeS₂ Crystal: “Discovering” the (400) Peak

Abstract

We discuss how a powder X-ray diffraction (XRD) system can be used to probe large pyrite (FeS2) crystals to reveal a peak generally not documented in the literature. The ability to detect this peak is attributed to the use of a large crystal, which gives large signal intensities. This type of experiment provides a research-like experience and gives students the opportunity to deepen their understanding of diffraction orders. In this experiment students are first challenged to be creative and determine how to mount a mineral crystal in a powder XRD system and then practice critical thinking in order to determine the origin of the unknown XRD peak. This experiment may also be generalized to crystals other than pyrite.

“Soft” oxidative coupling of methane to ethylene: Mechanistic insights from combined experiment and theory

“…After Fe 3 O 4 sulfurization, the predominant phase detected by pXRD is FeS (Fig. 2A) (43,44). These data differ slightly from our earlier report (34), reflecting improved instrumentation.…”

Fast-Growing Magnetic Wood Synthesis by an In-Situ Method

“…In a comparison of the results, the wood treated with the strong base precursor had more peaks according to the standard magnetite diffractogram. With the strong base precursor, no 2θ values were detected at 18.78 and 45.47 with Miller index values of 111 and 400, respectively; this may have happened because the diffraction signal in the crystal lattice was very weak due to the influence of a strong sample matrix background [ 45 ]; this crystal size is smaller than previously reported results [ 21 ], with the weak base being associated with a size of 16 nm. According to Sumadiyasa et al [ 47 ], the measurement results using the Scherrer equation represent the crystal size of a certain phase only (single phase); in our case, it was the magnetite phase.…”

“…In addition, cellulose can be hydrolysed by bases during the immersion process. With the weak base precursor, there was no detectable value of 2θ at 34.61; this may have happened because the diffraction signal in the crystal lattice was very weak due to the influence of a strong sample matrix background [ 45 ]. According to Dong et al [ 21 ], part of the crystalline structure in damaged wood is caused by magnetic treatment.…”

Structure Analysis from Powder Diffraction Data: Rietveld Refinement in Excel

“…It also leads to significant gaps developing between the theory students see in lectures and textbooks, and the way they experience crystallography in a practical setting. Several publications have previously raised the educational consequences, and there have been a number of earlier papers on how to build crystallographic education into school, undergraduate and postgraduate, curricula. − Several previous publications have described ways in which powder diffraction experiments can be introduced into undergraduate practical classes to highlight the importance of the technique itself, ,− or its use as a characterization method as part of a wider laboratory practical. − We are, however, unaware of other work that teaches structure analysis from powder diffraction data in the way described here.…”