Substitution of cations in crystals can lead to a corresponding change in anion concentration in a crystal. For example, if a cation is substituted by lower valent cation in an oxide material, oxygen vacancies will be created in the lattice for charge neutrality. How can we quantify it? What will be the suitable experimental procedure for that?
Thanks in advance...
Dear Vaisakhan Thampi:
Metal / oxygen can determine the quantitative of EELS analysis (Ultramicroscopy. 2011.V. 111. N2. p.123.)
Best regards.
The most common method is the dependence of the lattice parameters as function of the concentration of anions. To determine the concentration of anions can use the methods associated with the destruction of materials such as mass spectroscopy analysis methods or "wet" chemistry,.
By themselves, these methods do not give a clear answer, since a change in the concentration of anions can produce a more complex defects, such as interstitial cations. However, in this case the lattice parameters will increase with the anion deficit.
High precision measurements of gravimetric density has been used to quantify both vacancy and antisite defects by varying the stoichiometry (ratio between anions and cations). Caveat: this method has been used for bulk crystals, not films.
If you have a good understanding of defect formation in your material, a doping study would be enough. Here, you would have to develop a model for possible defect complexes and the resultant free charges for each mechanism. Then you could characterize materials synthesized under various conditions using Hall effect measurements.
A direct method for detecting vacancies is positron annihilation spectroscopy but the capability is relatively rare and may not help quantify the vacancy density, but the results can help identify trends with respect to growth conditions.
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