XRD (Powder)

Model – Xpert Pro MPD (Pananalytical)

The instrument is a PANalyticalX'Pert Pro MPD, powered by a Philips PW3040/60 X-ray generator and fitted with an X'Celerator* detector.Diffraction data is acquired by exposing powder samples to Cu-K_αX-ray radiation, which has a characteristic wavelength (l) of 1.5418 Å.  X-rays were generated from a Cu anode supplied with 40 kV and a current of 40 mA

Phase identification was carried out by means of the X'Pert accompanying software program PANalyticalHigh Score Plusin conjunction with the ICDD Powder Diffraction File 2 Database (1999), ICDD Powder Diffraction File 4 - Minerals (2012), the American Mineralogist Crystal Structure Database (March 2010) and the Crystallography Open Database

The X’Celerator is an ultra-fast X-ray detector that uses RTMS (Real Time Multiple Strip) technology.  It operates as an array of a hundred channels which can simultaneously count X-rays diffracted from a sample over the range of 2θ angles specified during a scan.  The X’Celerator is therefore able to give produce high quality diffraction data in a significantly shorter time period than an older style diffractometer would require.

Principle:-

Let us consider an X-ray beam incident on a pair of parallel planes P1 and P2, separated by an inter-planar spacing d.

The two parallel incident rays 1 and 2 make an angle (THETA) with these planes. A reflected beam of maximum intensity will result if the waves represented by 1’ and 2’ are in phase. The difference in path length between 1 to 1’ and 2 to 2’ must then be an integral number of wavelengths, (LAMBDA). We can express this  relationship mathematically in Bragg’s law.

2d*sin T = n * ?

The process of reflection is described here in terms of incident and reflected (or diffracted) rays, each making an angle THETA with a fixed crystal plane. Reflections occurs from planes set at angle THETA with respect to the incident beam and generates a reflected beam at an angle 2-THETA from the incident beam.

The possible d-spacing defined by the indices h, k, l are determined by the shape of the unit cell. Rewriting  Bragg’s law we get :

sin T = ?/2d

Therefore the possible 2-THETA values where we can have reflections are determined by the unit cell  dimensions. However, the intensities of the reflections are determined by the distribution of the electrons in the unit cell. The highest electron density are found around atoms. Therefore, the intensities depend on what kind of atoms we have and where in the unit cell they are located.

Planes going through areas with high electron density will reflect strongly, planes with low electron density will give weak intensities.

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