Table of Contents
Setup and Results
To study the effect of the wavelength and the detector noise using a laboratory powder diffractometer for determination of PDF and the maximum evaluable Q-value, a 1 mm glass capillary has been filled with Pigment Yellow 213 (1) (PY213) and adjusted on a goniometer head of a Stoe Stadi P powder diffractometer in Debye-Scherrer geometry at the Stoe & Cie application laboratory.
Setup and Results
Figure 1. Pigment Yellow 213, C23H21O9N5.
Data has been collected from set-ups with Cu-, Mo- and Ag-anode sealed tubes and the respective Ge(111)-monochromator for pure Kα1- radiation as well as a Dectris MYTHEN 1K detector equipped with a wavelength optimized chip (320, 450 or 1000 μm thickness), a linear and an IP-PSD.
Data evaluation has been performed by the Department of Inorganic Chemistry, Goethe University Frankfurt, using PDFgetX2 (2).
Figure 2. Background and powder pattern of PY213 measured with Cu- and lin. PSD, Moand IP PSD as well as Ag-radiation and MYTHEN 1K (large to small).
A Fourier transformation of the diffraction data F(Q) with Q=4∂(sinθ/λ) provides the observed PDF G(r), which, in turn, yields the probability to determine a pair of atoms in the distance r. It is possible to calculate the maximum theoretical Q value directly from 2θ (max) of the goniometer.
Figure 3. F(Q) for PY213 with Ag-radiation.
For the Stadi P, the Q(theo max) value could be 20 Å-1 for Ag-radiation, but the observed Q(max) value is very low. G(r) yields a Q(obs max) of approximately 7 Å-1, 10 Å-1 and 13 Å-1 for Cu-, Mo-, and Ag-radiation, respectively. For ESRF Synchrotron data with λ = 0.40 Å, Q(obs max) is found to be 14 Å-1 (3).
Figure 4. G(r) for PY213 measured with Cu-, Mo- and Ag-radiation (left to right).
As expected, the highest Q (obs max) is yielded by the shortest wavelength.
Figure 5. Stoe Stadi P with MYTHEN 1K.
The low noise and excellent resolution of the Dectris MYTHEN 1K make it the detector of choice. The pure Ag Kα1-radiation from the Ge(111) monochromator allows the Stoe Stadi P powder diffractometer to score as well in XRD as in PDF calculation.
1. Schmidt, M.U. et al., Acta Cryst. (2009). B65, 189-199
2. Qiu, X., Thompson, J.W. & Billinge, S.J.L. J. Appl. Cryst. (2004). 37, 678.
3. Presentation of Martin U. Schmidt, EPDIC, Warszawa, Sept. 2008
This information has been sourced, reviewed and adapted from materials provided by STOE.
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