Lattice trends in Ti₅Si₃Z_x (Z = B,C,N,O and 0<x<1)

Several Ti₅Si₃Z_x compositions (Z = boron, carbon, nitrogen and oxygen) were synthesized by arc-melting. Powder X-ray diffraction indicates the materials maintain the Mn₅Si₃-type structure of the binary compound Ti₅Si₃. Calculated cell constants were correlated to ternary composition based on chemical analysis. Nitrogen and oxygen additions to Ti₅Si₃ promote a cell volume decrease, while boron additions promote a cell volume increase. Carbon additions cause a decrease in the a-cell constant and an increase in the c-cell constant with a concomitant cell volume increase. Room temperature X-ray single crystal structural analysis was performed on one composition for each ternary addition. Each analyzed composition has the P6₃/mcm space group (No. 193) with the Mn₅Si₃-type structure. The ternary addition occupies the normally vacant interstitial site at the center of the trigonal antiprisms of titanium (Ti2) atoms (Ti₆Z polyhedra), located in chains at the corners of the hexagonal unit cell. Bonding between the interstitial atoms and the titanium (Ti2) atoms in the Ti₆Z polyhedra is indicated by a decrease in the Ti2-Ti2 and Ti2-Z atomic separations.