Schmahl, Wolfgang W.; Putnis, A.; Salje, E.; Freeman, P.; Graeme-Barber, A.; Jones, R.; Singh, K. K.; Blunt, J.; Edwards, P. P.; Loram, J.; Mirza, K. (1989): Twin formation and structural modulations in orthorhombic and tetragonal YBa2(Cu1-xCox)3O7-δ. In: Philosophical Magazine Letters, Vol. 60, Nr. 6: S. 241-248
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The microstructure of YBa2(Cu1-xCox)3O7-δ, prepared by the standard ceramic method, s, shows lamellar twin structures with decreasing spacings between twin walls with increasing Co content for x≲0.02, developing into 110-type cross-hatched ’tweed’ modulation for x≳0.02. Several wall junctions are found for x=0.02. The structural phase transition between macroscopically orthorhombic and tetragonal material occurs at x≈0.025; structural modulations (λ≈20 angstrom) persist in the samples with high Co content (x>0.25). The modulations lead to a considerable broadening of the X-ray lines affected by orthorhombic splitting and show maximum amplitude at the critical composition x≈0.025.