A mosaic of non-twinned single crystals was studied by means of muon spin rotation. The flux-line lattice in these crystals was found to be pinned. This pinning then led to disorder in the lattice. The average relative breathing mode lattice displacement was found to be about 0.8%. This value was comparable to that found for twinned samples. It was suggested that the origin of the pinning might be O vacancies.

W.J.Kossler, A.D.Goonewardene, A.J.Greer, D.L.Williams, E.Koster, D.R.Harshman, J.Z.Liu, R.N.Shelton: Physical Review B, 1997, 56[5], 2376-8