Rita John
University of Madras, India
Title: First principle calculations on the effect of addition of X (Co, Rh, Ir) on TiPd
Biography
Biography: Rita John
Abstract
Shape memory alloys are intermetallic compounds that have the ability to recover their original shape upon appropriate thermomechanical loading. TiPd, a prominent high temperature shape memory alloy (HTSMA) undergoes martensitic transformation (MT) from the parent B2 (cubic) phase to the product B19 (orthorhombic) phase. We have studied the effect of addition of X (Co, Rh, Ir) on the structural and electronic properties of TiPd shape memory alloys. The site preference of ternary additions X are determined from the calculated formation energy. It was found that X has strong preference for Ti sublattice for the composition considered. The cubic structure of B2 phase is maintained for the substitutional alloying of 6.25% of Ti/Pd sites with X. The density of states (total, site and angular momentum decomposed) are plotted for both Ti43.75Pd50X6.25 and Ti50Pd43.75X6.25 series. Higher stability of Ti43.75Pd50X6.25 is due to the decrease of d states of Ti and X at fermi level with increasing atomic number of X impurities. Though localization effect is more pronounced in Ti50Pd43.75X6.25 series with increasing atomic number of X, the number of d states of Ti remains same. It is Tid states at fermi level that determines the phase stability of these alloys. Also, we have investigated the impact of addition of varying concentration of magnetic impurity Co (6.25, 12.5, 25%) on B2 and B19 phases of TiPd. Band Jahn Teller broadening is observed in Ti25Pd50Co25 which is one of the accompanying features of MT. Band structure calculations are consistent with the results of density of states. Hole and electron pockets observed in the band structure are endorsed in fermi surfaces. Charge density contours are plotted which give an idea about electron charge distribution and nature of bonding.