EPR measurements at 95 GHz are carried on two samples in order to resolve a question on the presence of two or more phases in high temperature superconductors HTSC. The purity of YBa2Cu3O7 is usually determined by the absence of any EPR absorption. The presence of defects such as free Cu2+gives rise to an EPR absorption which can be useful in the characterization of the material. However, EPR absorptions also appear when a dilute rare earth RE magnetic ion is present, replacing a small amount of one of the constituents in YBa2Cu3O7, e.g. Gd replacing a small percent of Y or, Nd replacing a small percent of Ba. We seek to differentiate the EPR of substituents from that of defects. In YBa2Cu3O6+x the EPR of Cu2+is observed below Tc and shows no proximity effects except for the Meissner effect field broadening observed when free radicals are in contact with a superconducting phase; it must be part of a different phase. Conversely the absorption from I is observed only in the mixed state and disappears below T*for the given applied field. Higher concentrations of Nd3+in the Ba layer, e.g., I'pNd1.2Ba1.8Cu3O7, Nd1.3Ba1.7Cu3O7 and Nd1.4Ba1.6Cu3O7 show very broad EPR absorption characteristic of spin-spin interactions, with the concurrent lowering of Tc. These observations indicate that the presence of Nd3+in the Ba layer reduces the contact term at the Cu2+end defects in the -O-Cu-O- chains of I which are caused by its presence. Since EPR absorption is always observed above Tc in the superconducting samples of I, I': are the Cu2-end defects responsible, are the RE responsible, or are both responsible
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