Badanie substancji krystalicznych metodą dyfrakcji promieni X / Structural study and quantitative anlysis of crystalline substances with X-ray difraction method

 

Ćwiczenie umożliwia zapoznanie się z dyfraktometrią rentgenowską, która jest obecnie jedną z podstawowych metod eksperymentalnych stosowanych w fizyce fazy skondensowanej, krystalografii, czy szeroko pojętych badaniach materiałowych.

W ćwiczeniu wykorzystywany jest dyfraktometr rentgenowski Empyrean (PANalytical) pracujący w geometrii Bragga-Brentano (pionowej), wyposażony w lampę z anodą Cu oraz filtr Ni.

Eksperyment obejmuje przygotowanie próbki jednofazowej, wykonanie dyfraktogramu i jego analizę w celu wyznaczenia dokładnej wartości stałej sieci oraz analizę substancji wielofazowej w celu identyfikacji jej składu.

The teaching aim of this experiment is to introduce basic concepts of investigating matter by X-ray diffraction (XRD). Polycrystalline samples (single- and multiphase) are studied.The data are collected using Empyrean (PANalytical) difractometer working in the (vertical) Bragg-Brentano geometry (a ceramic X-ray tube with Cu anode and Ni flter are used). The diffraction pattern of a single phase sample, crystallizing in a cubic crystal structure, is analysed to obtain the values of the Bragg angle for all the observed Bragg reflections and then the Miller indices hkl are assigned to them.This allows to determine the type of the unit cell of the investigated crystal (usually NaCl, KCl or Si). The accurate value of the lattice constant is calculated by an extrapolation method.The experiment offers also an opportunity for pursuing a full and systematic analysis of the uncertainty of the evaluated lattice parameter. The XRD pattern of a multiphase sample is analysed to obtain qualitative information of the phase composition of the sample. As good texts on XRD (both on basic and advanced level) are easily accessible in the Internet as well as in the Faculty library, students have a unique opportunity to take their frst steps or develop their skills in quick and effective information gathering. This lab-exercise can be carried out not only in his basic version but it allows for a wide variety of personalized programs for ambitious students either suggested by a tutor or worked out by the students themselves (each project should be authorized by a tutor).