Unraveling the electronic structure, mechanical and physical properties of Ag alloyed $$\alpha $$ α - $$\hbox {Ta}_{\mathbf {5}}\hbox {Si}_{\mathbf {3}}$$ Ta 5 Si 3 via first-principles calculations

$$\alpha $$ α -Ta5Si3 is of considerable interest as a coating material for bioimplants. First-principles density-functional theory (DFT) calculations were performed to investigate the influence of Ag addition on the mechanical and physical properties of $$\alpha $$ α - $$\hbox {Ta}_{{5}}\hbox {Si}_{{3}}$$ Ta 5 Si 3 . The calculated enthalpies of formation indicated that the Ag atoms prefer to substitute the Ta atoms at 16l sites of the $$\hbox {D}8_{\mathrm{l}}$$ D 8 l structure crystal. With increasing Ag content, both the theoretical polycrystalline moduli and hardness of $$\alpha $$ α - $$(\hbox {Ta}_{1-\mathrm{x}}\hbox {Ag}_{\mathrm{x}})_{5}\hbox {Si}_{{3}}$$ ( Ta 1 - x Ag x ) 5 Si 3 compounds decreased while the anisotropy of elastic modulus increased. Modelling suggests that $$\alpha $$ α - $$(\hbox {Ta}_{1-{x}}\hbox {Ag}_{{x}})_{5}\hbox {Si}_{{3}}$$ ( Ta 1 - x Ag x ) 5 Si 3 compounds become ductile when the concentration of Ag exceeds 9.38 at.%, which may be attributed to weakening of the covalent bonds between Ta and Si atoms when Ta is substituted by Ag. The ternary compounds also exhibit higher anisotropy of thermal expansion coefficients relative to binary $$\alpha $$ α - $$\hbox {Ta}_{{5}}\hbox {Si}_{{3}}$$ Ta 5 Si 3 . Moreover, the addition of Ag to $$\alpha $$ α - $$\hbox {Ta}_{{5}}\hbox {Si}_{3} $$ Ta 5 Si 3 results in the increase of the acoustic velocity anisotropy and a reduction in the Debye temperature. Graphical abstract The mechanical and physical properties of Ag alloyed $$\alpha $$ α - $$\hbox {Ta}_5\hbox {Si}_3$$ Ta 5 Si 3 were calculated by first-principles density functional theory. Ag atoms are predicted to replace Ta atoms at 16l sites, thereby increasing the thermal expansion anisotropy, ductility and hardness of $$\alpha $$ α - $$\hbox {Ta}_5\hbox {Si}_3$$ Ta 5 Si 3 .