Influence of Oxygen on the Tribomechanical Properties of Single Crystals of YBa2Cu3O7−δ
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This paper reports a study on the mechanical and tribological properties of ab- and a (b) c−planes of YBa2Cu3O7−δ single crystals. The single crystals were grown using a CuO-BaO self-flux method. The oxygenation effect on the mechanical and tribological properties of ab- and a (b) c−planes is reported. For the ab- plane, the hardness and elastic modulus were around 6 and 50 GPa, respectively. In this case, significant differences were not observed among the hardness and elastic modulus at different oxygenation states. However, the hardness and elastic modulus for as-grown and oxygenated YBa2Cu3O7−δ single crystals were different from that of the a (b) c−plane, and were observed to be slightly higher for the as-grown than for the oxygenated samples. For as-grown and oxygenated samples, we observed hardness values around 4.7 and 2.0 GPa, respectively. Regarding the elastic modulus, the values were 75 and 40 GPa, respectively. The indentation fracture toughness values on the ab- plane for the as-grown and oxygenated YBa2Cu3O7−δ single crystal were 3.7 ± 1.2 and 2.9 ± 1.2 MPa m1/2, respectively. For the ab- plane, the scratch resistance of the as-grown sample was higher than that of the oxygenated sample and the scratches under load were deeper for the oxygenated sample. As regards the a (b) c−plane, the scar features were seemingly constant through all the scratch lengths and the scratches under load were deeper and larger for the oxygenated than that for the as-grown sample.
KeywordsYBCO Oxygenation Instrumented indentation Hardness Elastic modulus Fracture toughness Nanoscratch
The authors are grateful to the C-LABMU/UEPG for characterization facilities. The authors also thank Prof. Dr. Carlos M. Lepienski for the use of the instrumented indentation facilities.
This work was partially financed by CNPq under contact no. 472746/2013-8.
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