Principle of XRD JUNAID FOUAD KAREEM

DOÇ.DR. MEHMET MUZAFFER KARADAĞJEOLOJİ MÜHENDİSLİĞİ ANA BİLİM DALI

FEN BİLİMLERİ ENSTİTÜSELCUK ÜNİVERSİTESİ

J_F_KAREEM@yahoo.com 2015/11/10

X-ray powder diffraction is one of the most potential characterization tools and a nondestructive technique for characterizing both organic and inorganic crystalline materials. The method previously used for measuring phase identification, quantitative analysis and to determine structure imperfections of samples from various disciplines such as geology, polymeric, environmental, pharmaceutical, and forensic sciences. In recent years, the applications have become extended to characterize carbon based materials and their composite properties. X-ray diffraction is used widely for quantitative analysis of geological samples but studies which document the accuracy of the methods employed are not numerous.  

ABSTRACT

LIST OF CONTENTAbstract

1- Introduction

1-1 History

1-2 Introduction

1-3 XRD fundamental principle

2- Principle of X-Ray diffraction

3- The diffraction of X-Ray

4-XRD application

4-1 XRD in geology

5- The different between diffraction and reflection

6- Benefit of X-Ray and type of information obtain by XRD analysis

7- References

INTRODUCTION1-1 history

*Wilhelm Conrad Röntgen discovered 1895 the X-rays.

*1901 he was honored by the Noble Prize for physics.

*1895- roentgen discovers X-rays:-

X-rays are high-frequency electromagnetic radiation with energy intermediate between far-UV and gamma ray regions figure (1). This leads to development in numerous fields, particularly medical.

*1911- Barkla recognized characteristic radiation:-

This scientist recognizes that x-rays emitted from different elements produce x-rays of different energy and wavelength.

Figure 1 Waves chart

1-2 INTRODUCTION

 

X-ray diffraction (XRD) is a popular analytical technique, which has been used for the analysis of both molecular and crystal structures, qualitative identification of various compounds, quantitative resolution of chemical species ,measuring the degree of crystallinity, isomorphous substitutions , stacking faults , polymorphisms , phase transitions , particle sizes etc. When X-ray light reflects on any crystal, it leads to form many diffraction patterns and the patterns reflect the physico-chemical characteristics of the crystal structures. In powder specimen, diffracted beams are typically come from the sample that reflects its structural physico-chemical features. Thus XRD technique can analyze structural features with other ambiguities of a wide range of materials such as inorganic catalysts, superconductors, biomolecules, glasses, polymers and so on .Analysis of these materials largely depends on forming diffraction patterns. Each material has its unique diffraction beam, which can define and identify the material by comparing the diffracted beams with reference database in JCPDS (Joint Committee on Powder Diffraction Standards) library.

Since the performance of the first X-ray diffraction experiments on a single crystal in 1912, X-ray crystallography has been of major importance in natural sciences and especially in mineralogy. X-ray diffraction provided the ideal means to understand structures of minerals (and other crystalline matter) on an atomic scale. It thus established relationships between the crystal structure and the physical and chemical properties of the material under investigation. In other cases it related the crystal structure to the special thermo dynamical conditions under which a mineral (or a rock) has been formed and thus provided important information for petrology and geology.

1-3 XRD FUDAMENTAL PRINCIPLEIn XRD, monochromatic X-ray beams focused on sample material to resolve structural information in the crystal lattice. Usually, the materials are composed of repeating uniform atomic planes which make up their crystal. Typically, polychromatic X-rays are produced in a special tube called cathode- ray tube. Filtering polychromatic X-rays through a monochromatic produces monochromatic radiation which hits onto the material atomic planes, separating the diffracted, transmitted and absorbed rays. X-rays are produced within a closed tube under vacuum atmosphere.

2- PRINCPLE OF X-RAY DIFFRACTIONThe most prevalent type of diffraction to X-ray crystallography is known as Bragg diffraction, which is define as the scattering of waves from a crystalline structure. Formulated by William Lawrence Bragg, the equation of Bragg's law relates wavelength to angle of incidence and lattice spacing (1), where n is a numeric constant known as the order of the diffracted beam, is the wavelength of the beam, d denotes the distance between lattice planes, and represents the angle of the diffracted wave. The conditions given by this equation must be fulfilled if diffraction is to occur.(1) 2 d sin

Because of the nature of diffraction, waves will experience either constructive (Figure 2) or destructive (Figure 3) interference with other waves. In the same way, when an X-ray beam is diffracted off a crystal, the different parts of the diffracted beam will have seemingly stronger energy, while other parts will have seemed to lost energy.

This is dependent mostly on the wavelength of the incident beam, and the spacing between crystal lattices of the sample. Information about the lattice structure is obtained by varying beam wavelengths, incident angles, and crystal orientation.

Fig 2 Schematic representation of constructive interference.

Figure 3: Schematic representation of destructive interference.At the directions satisfying Bragg law, the rays scattered by all the atoms in all the Planes are completely in phase and reinforce each other (constructive interference) to form a diffracted beam in the direction. In all other directions of space the scattered beams are out of phase and annul one another (destructive interference).It is helpful to distinguish 3 scattering modes:1. by atoms arranged randomly in space, as in a monotomic gas. This scattering occurs in all directions and it is weak.2. by atoms arranged periodically in space, as in a perfect crystal:(a) In a very few directions, those satisfying the Bragg law, the scattering is strong and is called diffraction. Amplitudes add (constructive interference).(b) In most directions, those not satisfying Bragg law, there is no scattering because the scattered rays cancel one another (destructive interference).

3- The diffraction of X-RayIn the year 1912, Friedrich, Knipping and von Laue performed the first diffraction experiment using single crystals of copper sulfate and zinc sulfite. Based on these experiments Max von Laue developed his theory of X-ray diffraction. At the same time W. L. Bragg and W. H. Bragg performed their diffraction experiments and in turn used an alternative though equivalent way of explaining the observed diffraction phenomena. Up to now the so-called Laue conditions and the Bragg equation are the basis of X-ray diffraction of crystalline material and it is therefore inevitable to start any monograph on X-ray crystallography with a short resume of the investigations carried out by these scientists.

Like visible light an X-ray beam is an electromagnetic wave characterized by an electric field vector E which is perpendicular to the direction of propagation and a magnetic field vector H which in turn is perpendicular both to E and the direction of propagation. Yet compared to an optical wave the wavelength of an X-ray beam is considerably shorter: thus the spectra of visible light comprises the range from 4000 to 7000A0, while X-rays have typically wavelengths between 0.1 to 10A0.

Due to the fact that X-ray wavelengths are comparable to the interatomic distances within a crystalline material one observes characteristic interactions between the X-rays and the ordered array of electrons in the crystal structure. These interactions make X-rays the most important source for the investigation of crystal structures.

If the electromagnetic X-ray waves encounter an object, they are scattered by the electrons of the object. The field of the X-rays forces the electrons within the material to oscillate and the electrons are in turn the starting point of secondary waves of the same frequency and wavelength like the primary waves. These waves superimpose and if constructive interference occurs give rise to the different diffraction phenomena which are generally strong if the distances within the object are comparable to the wavelength of the incoming beam. In addition the periodic nature of the atomic arrangement within a crystal gives rise to special diffraction phenomena which are in many ways comparable to the diffraction of visible light by a refraction lattice.

4-XRD ApplicationsAlthough transmission electron microscope (TEM), scanning electron microscope (SEM) and electron diffraction spectroscopies are popularly used to characterize the novel materials, these morphological probes can depict only the local features. Thus there is a room for global probes such as XRD for the complete characterization of the bulk carbon matters. In addition, as a popular analytical tool XRD has widespread applications in the fields of geology, pharmaceuticals, materials, polymers, environmental and forensic investigations. In addition, it finds out materials identity, crystallinity, residual stress and textural features with minimum invasion. It has long been used in immigration for detecting and identifying censored drugs, materials and coins.

4-1 XRD in geologyAcid rock drainage precipitates various minerals which are often characterized by XRD to extract information about the earth mineralogical composition. Optical analyzes of these fine grained minerals are often difficult and sometimes impossible. For instance, optical light microscopy cannot recognize finely grained mineralogical sample which could be easily examined by the XRD pattern analysis With the reference intensity ratio method or others. It can identify clay rich minerals which can prevent big landslides and mudflows. XRD software can be used to simulate major, minor, and trace elements in coal beds with evaluating vertical and lateral variations of mineral matters. Quantification power of XRD has further broadened its application in geochemistry.

It can quantify various minerals, measure hydration properties, degree of crystallinity and deviations from the native structure in great ease. Geologists can use this technique as a reliable and fast characterizing tool to compile major and trace elements, calculate degree of clay mineralization and phase analysis. XRD can measure specimen purity, find out mismatch lattice, deduce stress and strains, calculate unit cell dimensions, and perform quantification. Additionally, it can discover dislocation density, roughness, density and thickness of thin film. However, anomalies in layered crystals, cationic substitution effects, orientation defects, small grain sizes and imperfect crystal might complicate geometrical analysis using XRD techniques.

5-The different between diffraction and reflection

The diffraction of x-rays by crystals and the reflection of visible light by mirrors appear similar, since in both phenomena the angle of incidence is equal to the angle of reflection. However, diffraction and reflection differ fundamentally in at least 3 aspects:

1. The diffracted beam from a crystal is build up of rays scattered by all the atoms of the crystal which lie in the path of the incident beam. The reflection of visible light takes place in a thin surface layer only.

2. The diffraction of monochromatic x-rays takes place only at those particular angles of incidence which satisfy the Bragg law. The reflection of visible light takes place at any angle of incidence.

3. The reflection of visible light by a good mirror is almost 100 percent efficient. The intensity of a diffracted x-ray beam is extremely small compared to that of the incident beam.

 

6-The benefit of X-ray diffraction *XRD Techniques give information about the structure of solids, the arrangement of the atoms that compose the solid.

*XRD permits nondestructive structure analyses, although is relatively low in sensitivity.

*disclose the presence of a substance (compound), not in terms of its constituent Chemical element.

*All compounds would be disclosed in the diffraction pattern.

6-1 type of information obtain by XRD analysis

- The kinds of materials that compose a solid (Qualitative analysis).

-The quantity of materials that compose the solid (Quantitative analysis).

-The quantity of materials that are crystallized (crystallinity).

-The amount of stress present in the solid (residual stress).

-The size of crystallites that compose the solid (crystallite size).

-Average orientation of crystallites that compose the solids (texture).

References1-S. HILLIER. 8 April 1999 Accurate quantitative analysis of clay and other minerals in sandstones by XRD: comparison of a Rietveld and a reference intensity ratio (RIR) method and the importance of sample preparation.

2-Wayne Lin and Andrew R. Barron. An Introduction to X-ray Diffraction.

3-Robert E. Dinnebier & Karen Friese, Max-Planck-Institute for Solid State Research, Stuttgart. FRG.

4-Rasel Das, Md. Eaqub Ali and Sharifah Bee Abd Hamid. Nanotechnology and Catalysis Research Center, University of Malaya, 50603 Kuala Lumpur, Malaysia October 25, 2013 current application of x-ray powder diffraction.