Nanoscratch and indentation fracture toughness in superconductor Ba-Fe-As single crystals with lamellar structure

Tribological aspects of Ba(Fe0.974Mn0.026)2As2 single crystals were analyzed through nanoscratch tests and correlated with fracture toughness data. The ~100 µm thick samples present ab-planes stacked by following the c-axis (lamellar structure). Scratch hardness (0.31 GPa for ab-plane and 2.10 GPa for a(b)c-plane) and wear rate are in accordance with previous results for indentation hardness. Microcracking rules the scratching behavior of both planes, the ab-one presenting a marked critical load for cracking that is loading-rate dependent. Fracture toughness, estimated by the minimum load for crack nucleation in indentation tests, was statistically similar, 1.8±0.9 MPa m1/2 for the ab-plane and 1.5±0.5 MPa m1/2 for the a(b)c-plane. Results lead to the conclusion that the lamellar structure determines the material tribo-mechanical behavior.