Analysis of the dc-resistivity of YBa2Cu3Ox: Deduction of the intragrain resistivity

The resistivity (100 K) scatters very much for YBa₂Cu₃O_x prepared as single crystals, epitaxial films or bulk samples which consist of grains of 1 to 10 m diameter. An analysis of (T) for granular bulk samples is presented indicating the existence of a low intrinsic resistivity ⁱ (T)= _0L ⁱ + ⁱ T with _0L ⁱ 0 and ⁱ 0.5µcm/K. The large grain boundary resistivity _b between the grains (>1 m) yield a macroscopic percolative conduction path lengtheningL/L ₀>1 with a reduced effective cross sectionC<C ₀ and thus, (T)= _b +(LC ₀/L ₀ C)· ⁱ (T). Evidence is presented for weak links inside single crystals and grains.