Room-Temperature Powder X-ray Diffraction (RT-PXRD)
Room-Temperature Powder X-ray Diffraction (RT-PXRD) stands as a fundamental technique in materials science, allowing researchers to probe and understand the crystallographic structure of a diverse array of substances at ambient conditions. Unlike traditional X-ray diffraction methods, RT -PXRD operates at room temperature, making it particularly versatile for the study of materials under real-world conditions.
In this technique, a powdered sample is exposed to X-rays, resulting in a diffraction pattern that can be analyzed to reveal crucial information about the material's crystalline structure, phase composition, and degree of crystallinity. RT-PXRD is invaluable for both qualitative and quantitative analysis, offering researchers a non-destructive means to explore the atomic arrangements within various materials, ranging from pharmaceuticals and polymers to metals and ceramics. This method's adaptability and precision make it an indispensable tool for elucidating the structural properties of materials that have implications across industries, facilitating advancements in material design, quality control, and performance optimization.
Conventional vs Synchrotron XRD
Conventional X-ray diffraction (XRD) uses lab-based X-ray sources and provides limited resolution and sensitivity. In contrast, synchrotron XRD utilizes synchrotron radiation, offering higher intensity, tunable wavelengths, and superior resolution, enabling detailed analysis of complex materials and structures. Synchrotron radiation possesses features ideal for XRD, including (a) intense X-rays, surpassing conventional analyzers by 100 to 1000 times; (b) precisely focused beams for enhanced resolution; (c) a broad energy spectrum; and (d) a brief pulsed time structure. These attributes result in elevated signal-to-noise ratios and angular resolution, reducing peak overlap and enhancing peak positioning, as illustrated in Figure 1.
Reference:
Khan H, Yerramilli AS, D'Oliveira A, Alford TL, Boffito DC, Patience GS. Experimental methods in chemical engineering: X-ray diffraction spectroscopy—XRD. Can J Chem Eng 2020;98:1255–66.
https:// doi.org/10.1002/cjce.23747.
Sensor Development
The materials' phase composition and crystallinity were assessed through the analysis of X-ray diffraction (XRD) spectra. Examination of the XRD spectra indicates that both the powder and the sintered material consist solely of a single crystalline phase, characterized by platinum with the Fm3m crystal structure (depicted in Figure 2a,b). The XRD spectrum of the powder reveals an amorphous halo in the scattering angle range of 2θ = 29° – 39°, implying the presence of an amorphous phase, likely represented by a platinum oxide, given the identification of platinum atoms as constituents of the PtO compound. Figure 2c displays the patterns of the prepared mixture and the crystalline phases used in the refinement, with the refinement process revealing 14.5 wt.% metallic platinum phase and 85.5 wt.% ZnO in the total mass of crystalline phases within the powder mixture. Consequently, the metallic platinum phase content in the platinum-based powder can be computed as (14.5/85.5) x 100%, resulting in approximately 17.0 wt.%. The remaining 83.0 wt.% is attributed to the amorphous phase.
Reference:
Volkov IA, Simonenko NP, Efimov AA, Simonenko TL, Vlasov IS, Borisov VI, et al. Platinum-based nanoparticles produced by a pulsed spark discharge as a promising material for gas sensors. Appl Sci 2021;11:1–20.
https: //doi.org/10.3390/app11020526.
Nanomaterials
High-resolution X-ray diffraction (XRD) measurements validate the lattice observed in the nanoparticles. Figure 3 illustrates XRD contraction patterns of bulk NiO (b-NiO) and nanosized NiO (25-NiO and 5-NiO). The upper spectrum ( a) corresponds to the b-NiO sample, the middle spectrum (b) to 25-NiO, and the lower spectrum (c) to the 5-NiO sample. To facilitate comparison with the less-intense nanoparticle spectra, the XRD spectrum for b-NiO was scaled down to 20% of its absolute intensity. No impurity peaks were detected in the XRD patterns, and all spectra—b-NiO, 25-NiO, and 5-NiO—align with NiO rock salt symmetry, as per the Joint Committee on Powder Diffraction Standards (JCPDS) file for pure NiO product (JCPDS File Card No. 71-1179). Figure 3 demonstrates that the diffraction peaks are significantly broadened in both nanosized NiO samples, attributable to their small crystallite size. The effect was quantified through XRD analysis, yielding an average particle size of 25.2 nm for 25-NiO and 4.8 nm for 5-NiO. Additionally, XRD for the nanosized NiO samples indicates a shift in peaks towards higher values of 2θ, signing a slight lattice contraction compared to the bulk crystallite sample.
Reference:
Peck MA, Langell MA. Comparison of nano-scaled and bulk NiO structural and environmental characteristics by XRD, XAFS, and XPS. Chem Mater 2012;24:4483–90.
https://doi.org/10.1021/cm300739y.
Geology
XRD is primarily utilized to ascertain the structural parameters of carbonaceous materials, particularly in the context of coal characterization. These parameters, such as carbon stacking layer spacing (d002), average lateral sizes (La), and stacking height of crystallite (Lc), serve to describe the three-dimensional carbon-filled structure within coal. The analysis using XRD also reveals the presence of a significant quantity of disordered substances and amorphous carbon in coal, with a gradual decrease observed during the coalification process. The XRD spectra of five middle-high-rank coal (MHRC) samples are depicted in Fig. 4, showcasing consistent graphite characteristics and notable background intensity. This suggests the inclusion of highly disordered materials in the form of amorphous carbon within the coal samples. Two distinct peaks, namely the 002 and 100 bands, are evident, with corresponding diffraction angles around 26° and 47°, respectively (Fig. 4). The 002 band is associated with the stacking between aromatic rings, representing microcrystals in polycondensed aromatic rings. On the left side of the 002 peak is the γ band, attributed to aliphatic hydrocarbon branch chains, various functional groups, and alicyclic hydrocarbons connected to the condensed aromatic rings.
Reference:
Jiang J, Yang W, Cheng Y, Liu Z, Zhang Q, Zhao K. Molecular structure characterization of middle-high rank coal via XRD, Raman and FTIR spectroscopy: Implications for coalification. Fuel 2019;239:559–72.
https: //doi.org/10.1016/j.fuel.2018.11.057.