X-ray diffraction (XRD) knowledge summary(3)

1. Principles for comparing sample cards with standard cards?

A few principles are provided for your consideration:

Contrast d-values are more important than contrast intensities; Lower angle lines to be more important than higher angle lines; Stronger lines to be important than weaker lines; To give importance to characteristic lines; There may be multiple sets of diffraction data for the same object phase, but be aware that some are deleted; Individual low angle lines appear to be missing; Changes in the strength of certain lines due to sample merit orientation; Sometimes there are unexplained weak lines, which is normal, and it cannot be required to get all the lines explained.

2. “Attention should be paid to characteristic lines”, then what are characteristic lines?” There may be several sets of diffraction data for the same phase, but be aware that some of them are deleted.

The so-called characteristic line is the strongest and unique line of a substance that is easiest to determine, for example, the characteristic line of quartz is the line with d=3.34Å. If this line appears in the mixture, there is a high probability that there is quartz, and the other lines are also the same, which is very useful for checking the phases of the substance in the mixture.

There may be more than one set of diffraction data for the same phase means that there are more than one card with data for a single phase. For example, quartz (SiO2) has data from Volumes 1 to 49, with a total of 93 data cards, but Volumes 1-8, 15, 16, 33-1161, 42-391, etc. (a total of 38 cards) have been deleted by the editors of the card library.

3. How can I convert single crystal data into powder for my standardized spectra?

You can use Shape's software to calculate powder theory diagrams from single crystal data.

4. I don't have its powder ray diagram, but I have the cell parameters deduced from its single crystal X-ray diffraction, how can I back deduce the powder diffraction diagram of this crystal?

If you have the structural data, you can calculate the powder diffraction diagram theoretically by using the reflex plus module of Materials Studio; if you have the atomic coordinates, you can also get its powder XRD diagram by diamond.

5. How can we analyze the crystal structure to determine if it is the substance we expect?

If you can find the diffraction data of your desired substance in ICDD's powder diffraction database, you may be able to analyze the crystal structure and determine that it is the desired substance.

6. What are the standard cards for lithium cobalt? Many manufacturers use the 16-427 standard card, which does not take into account the (009) diffraction peak, so why not use the 75-0532 standard card?

16-427 is derived from experiments, while 75-0532 is calculated by using the structure data in the ICSD structure database. When doing experiments on lithium cobalt, the peaks appearing are the same as those of 75-0532, and is there only a difference in the diffraction peak of (009) between 16-427 and 16-427? If so, then it is 16-427 missed this peak, or the angle of the experimenter at that time when collecting data was not high enough to reach the position of this peak, which is often the case.

7. When doing lithium cobaltate XRD diffraction experiments, the diffraction pictures made on the X diffractometer, the first diffraction peak is particularly high, and the other diffraction peaks are particularly low, disproportionate, is it because of the instrument itself, or is it a meritocracy, please give me some advice from your experts.

I don't know if you did the experiment with lithium cobalt oxide powder, or polycrystalline film, etc.? If it's a powder, then it's probably a case of selective orientation.

8. When magnesium ammonium phosphate was crystallized from ammonia-nitrogen wastewater by chemical precipitation, the diffraction peaks were regularly shifted to the left by XRD when compared with standard JCPDS, so what kind of information about the crystal structure is expressed?

If the shift of the peaks is essentially a fixed value, the reason is that the 2θ zero position is incorrect, the sample plane is tilted back, the composition deviates from the chemical formula, and the unknown deviation causes the lattice to become a bit larger.

9. Can quantitative XRD analysis be performed with Jade5 software?

The basic data for quantitative XRD analysis are the intensities of the constituent phases of the sample (in principle, the peak areas should be used), the rest of the work is multiplication and division ratios, which can be easily accomplished with a spreadsheet software (e.g., WPS Ofice's “WPS Spreadsheets”, Microsoft's Excel). Therefore, any software tool that can obtain peak area or peak height can be used for quantitative XRD analysis, of course, Jade software is more convenient.