I want to resolve a issue and kind of mystery to me being a research scholar for the apatite materials. Generally apatite shows P63/m space group when we perform refinement from the XRD data. The issue arises as P63/m do not fit well to explain the vibrational modes(IR or RAMAN) as the DFT calculations suggests wrong results (as read in many papers) and says P63 is the best space group for apatite materials. Many papers says XRD shows an averaging effect nature and a result there is no issue when we perform refinement by P63/m and P63 space group do not fits well during the refinement. Till now its issue has not been yet resolved and I want to solve it. How should I proceed to tackle such kind of situations?
Dear Anshul Sharma
As it till now your issue has not been yet resolved and you want to solve it, and you asking how should you proceed to tackle such kind of situations. Yes, the golden key word to open the knowledge gate in this repect is "stoichiometric". In this respect, the hydroxyapatite (HAP) and related minerals by vibrational spectroscopy has been ongoing for long time ago in an effort to understand its structure and the variations that arise as a result of substitutions in the apatite lattice . While these efforts have been quite successful for stoichiometric, well crystallized apatites. non-stoichiometric HAP is poorly crystalline relative to the stoichiometric mineral, and its vibrational bands are broad. Unlike the spectroscopic features of stoichiometric HAP, they do not sharpen noticeably on cooling the sample. It has been shown by low temperature Raman studies that stoichiometric HAP has a space group symmetry of P63 where not revealed by non-stoichiometric HAP. Farther-more the second derivative (2DR) calculations were used to resolve the IR spectrum of stoichiometric HAP where again not solved for non-stoichiometric HAP. Hope your issue is solving well. Best regards from retired engineer, Mohammed Hussein j. H. Al'Atia .
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