International
Tables for
Crystallography
Volume H
Powder diffraction
Edited by C. J. Gilmore, J. A. Kaduk and H. Schenk

International Tables for Crystallography (2018). Vol. H, ch. 3.10, pp. 376-377

Section 3.10.3. Analytical techniques

L. León-Reina,a A. Cuesta,b M. García-Maté,c,d G. Álvarez-Pinazo,c,d I. Santacruz,c O. Vallcorba,b A. G. De la Torrec and M. A. G. Arandab,c*

aServicios Centrales de Apoyo a la Investigación, Universidad de Málaga, 29071 Málaga, Spain,bALBA Synchrotron, Carrer de la Llum 2–26, Cerdanyola, 08290 Barcelona, Spain,cDepartamento de Química Inorgánica, Cristalografía y Mineralogía, Universidad de Málaga, 29071 Málaga, Spain, and dX-Ray Data Services S.L., Edificio de institutos universitarios, c/ Severo Ochoa 4, Parque tecnológico de Andalucía, 29590 Málaga, Spain
Correspondence e-mail:  g_aranda@uma.es

3.10.3. Analytical techniques

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All phases and mixtures were studied with Mo Kα1 (transmission geometry) and Cu Kα1 (reflection geometry) monochromatic radiation. Table 3.10.1[link] shows the X-ray linear absorption coefficients for all of the phases, as microabsorption is always a concern in RQPA. A microabsorption correction was not applied in this work, but readers must be aware that this effect, if relevant, is one of the greatest source of inaccuracy in RQPA (Madsen et al., 2001[link]; Scarlett et al., 2002[link]). All of the phases were also characterized by scanning electron microscopy (see Fig. 3.10.2[link]).

[Figure 3.10.2]

Figure 3.10.2 | top | pdf |

Scanning electron microscopy micrographs for the studied phases (×1000). The inset in the zincite micrograph shows the powder at higher magnification (×20 000).

3.10.3.1. Mo Kα1 laboratory X-ray powder diffraction (LXRPD)

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Mo Kα1 powder patterns were collected in transmission geometry in constant irradiated volume mode, in order to avoid any correction of the measured intensities, on a D8 ADVANCE (Bruker AXS) diffractometer (188.5 mm radius) equipped with a Ge(111) primary monochromator, which gives monochromatic Mo radiation (λ = 0.7093 Å). The X-ray tube operated at 50 kV and 50 mA. The optics configuration was a fixed divergence slit (2°) and a fixed diffracted anti-scatter slit (9°). A LYNXEYE XE 500 µm energy-dispersive linear detector, optimized for high-energy radiation, was used with the maximum opening angle. Using these conditions, the samples were measured between 3 and 35° 2θ with a step size of 0.006° and with a total measurement time of 3 h 5 min. The flat samples were placed into cylindrical holders between two Kapton foils (Cuesta et al., 2015[link]) and rotated at a rate of 10 revolutions per minute during data collection. Moreover, the absorption factor of each sample was experimentally measured by comparing the direct beam with and without the sample (Cuesta et al., 2015[link]). The amount of sample loaded (which determines the height of the cylinder) in the holders was adjusted to obtain a total absorption (μt) of ∼1, which corresponds to an absorption factor of ∼2.7 or 63% of direct-beam attenuation. For the organic samples this criterion was not followed as it would lead to very thick specimens. In this case, the maximum holder thickness was used (1.7 mm).

3.10.3.2. Cu Kα1 laboratory X-ray powder diffraction (LXRPD)

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Cu Kα1 powder patterns for exactly the same samples were recorded in reflection geometry (θ/2θ) on a X′Pert MPD PRO (PANalytical B.V.) diffractometer (240 mm radius) equipped with a Ge(111) primary monochromator, which gives monochromatic Cu radiation (λ = 1.54059 Å). The X-ray tube was operated at 45 kV and 40 mA. The optics configuration was a fixed divergence slit (0.5°), a fixed incident anti-scatter slit (1°), a fixed diffracted anti-scatter slit (0.5°) and an X′Celerator RTMS (real-time multiple strip) detector operating in scanning mode with the maximum active length. Using these conditions, the samples were measured between 6.5 and 81.5° 2θ with a step size of 0.0167° and a total measurement time of 2 h 36 min. The flat samples were prepared by rear charge of a flat sample holder in order to minimize preferred orientation and were rotated at a rate of 10 revolutions per minute.

The lowest analyte content samples, CGpQ_0.12A and GFL_0.12X, were measured three times using both radiations, Mo Kα1 and Cu Kα1, for a precision (reproducibility) assessment. Therefore, regrinding and reloading of the mixtures in the sample holder was carried out prior to every measurement.

3.10.3.3. Transmission synchrotron X-ray powder diffraction (SXRPD)

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Powder patterns for the lowest analyte content samples, CGpQ_0.12A and GFL_0.12X, were also measured using synchrotron radiation. SXRPD data were collected in Debye–Scherrer (transmission) mode using the powder diffractometer at the ALBA Light Source (Fauth et al., 2013[link]). The wavelength, λ = 0.77439 (2) Å, was selected with a double-crystal Si(111) monochromator and was determined using the NIST SRM640d Si standard (a = 5.43123 Å). The diffractometer is equipped with a MYTHEN-II detector system. The samples were loaded into glass capillaries 0.7 mm in diameter and were rapidly rotated during data collection to improve the diffracting-particle statistics. The data-acquisition time was 20 min per pattern to attain a very good signal-to-noise (S/N) ratio over the angular range 1–35° 2θ. Three patterns, taken at different positions along the capillaries, were collected for each sample.

SXRPD data for the amorphous content series, CZQ_xGl, were also measured at the ALBA Light Source. The experimental setup was the same as described above but the working wavelength was λ = 0.49591 (2) Å.

References

Cuesta, A., Álvarez-Pinazo, G., García-Maté, M., Santacruz, I., Aranda, M. A. G., De la Torre, Á. G. & León-Reina, L. (2015). Rietveld quantitative phase analysis with molybdenum radiation. Powder Diffr. 30, 25–35.Google Scholar
Fauth, F., Peral, I., Popescu, C. & Knapp, M. (2013). The new material science powder diffraction beamline at ALBA synchrotron. Powder Diffr. 28, S360–S370.Google Scholar
Madsen, I. C., Scarlett, N. V. Y., Cranswick, L. M. D. & Lwin, T. (2001). Outcomes of the International Union of Crystallography Commission on Powder Diffraction Round Robin on Quantitative Phase Analysis: samples 1a to 1h. J. Appl. Cryst. 34, 409–426.Google Scholar
Scarlett, N. V. Y., Madsen, I. C., Cranswick, L. M. D., Lwin, T., Groleau, E., Stephenson, G., Aylmore, M. & Agron-Olshina, N. (2002). Outcomes of the International Union of Crystallography Commission on Powder Diffraction Round Robin on Quantitative Phase Analysis: samples 2, 3, 4, synthetic bauxite, natural granodiorite and pharmaceuticals. J. Appl. Cryst. 35, 383–400.Google Scholar








































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