Melt-powder-melt-grown crystals of high-Tc YBa2Cu3O7-δ were prepared from different chemical starting compositions. They all show well textured microstructures with characteristic differences and various amounts of included phases (Y2BaCuO5, Ba4Cu2PtO9, and metallic silver) depending on the starting composition. Detailed investigations with polarized reflected light, XRF, EDX and X-ray diffraction reveal characteristic features of the microstructure such as the distribution of included phases as well as twinning and crack formation, which are related to local variations in oxygen content in these materials. Increasing silver contents result in a reduction of cracking. The occurence of domain-like regions with distinct large twin lamellae is correlated with the distribution of Y2BaCuO5 inclusions.
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