Defect Chemistry of Anhydrous and Hydrous Ti Doped Olivine

Raj, Vivek (2022) Defect Chemistry of Anhydrous and Hydrous Ti Doped Olivine. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Vivek Raj (16MS163)) 16MS163_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (2MB)

Abstract

Here, we are interested in incorporation of Ti in both hydrous and anhydrous olivine.It is now well established that including charged impurity defects can significantly alter defect characteristics (Kittel 1986, Phillips 1973). Berry et al. 2005; Tollan et al. 2017, 2018; Cline et al. 2018 have all reported on the importance of Ti in modulating the effect of H+ on the physical characteristics of olivine. Dai and Karato (2020) looked into the effect of Ti and H inclusion on olivine electrical conductivity. We will also study the defect chemistry of other minor elements(like Cr, Mn, Ca, Ni) doped olivine and we will make a general idea of how incorporation of minor elements in olivine affect defect chemistry of both hydrous and anhydrous olivine. And as olivine is an abundant mineral in earth’s upper mantle, any changes in it will also affect the mantle. Using first principle density function theory, we have calculated energy of structures and tried to find lowest energy structure so that we can find the favorable way of incorporation of Ti in hydrous and anhydrous forsterite (Mg₂SiO₄) as well as Fe containing forsterite i.e, olivine (Fe,Mg)₂SiO₄. After finding the most favorable way for incorporation of Ti in forsterite/olivine in hydrous and anhydrous conditions, we also did study the effect of Ti doping on the structure and properties of the forsterite/olivine. Here, we will see how the presence of water affects the incorporation of Ti in forsterite/olivine. In absence of water, Ti wants to sit at a tetrahedral site, i.e. Ti will be substituted for Si⁴⁺ in forsterite /olivine. However, in the presence of water, Ti will go and sit at octahedral M1 site and Si vacancy will be followed by substitution of 2H atoms at Si tetrahedral site. From the density of the state plot we can see that electrical conductivity of structure increases with doping of Ti, as we can see that the band gap between valence and conduction band decreases with doping of Ti in the structure in anhydrous condition.where in hydrous condition electrical conductivity decreases after doping Ti

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