In: Physics
Using powder X-ray diffraction to analyse a metal compound, a simple pattern of peaks resulted, where the largest peak existed at an angle of 2θ= 19.8°. However, when a similar sample was analysed that contained a metallic impurity, this 2θ value became 22.4°. What does this suggest is happening to the crystal lattice and why?
According to Bragg diffraction condition () we know that diffraction angle and inter-planer spacing are inversely related with each other
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Therefore in the preset case, the increase in diffraction angle from to is associated with the decrease in the inter-planer spacing d. Therefore, with the incorporation of metallic impurity in the sample, d value decreases. The decrease in d value is associated with the compressive strain in the lattice. In other words, metallic impurities distort the original crystal structure of the lattice by varying bond lengths, bond angles etc. and hence, changes the lattice parameter. Such distortion arises due to the random incorporation of the metallic impurities in the lattice.