Non-Ohmic behaviour and phase transitions in YBa2Cu3O7-δwith high normal resistivity

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Abstract
The electrical resistivity in polycrystalline YBa2Cu3O7- delta with high normal resistivity has been investigated extensively in the temperature range 78c0=92.24 K; (ii) for 84 Kc0 the I-V relation deviates slightly from Ohm's law, but if it is approximated by V approximately= alpha 1I, the parameter alpha 1 can be described by alpha 1 approximately=exp(-2 mod b(Tc0-Tc)/(T-Tc) mod 12/), with Tc=78.9 K and b=3.2; (iii) in the temperature range Tca(T), where the exponent a(T) increases with decreasing temperature and reaches a approximately=3 at Tc; and (iv) below Tc, the resistivity rho is reduced to zero. The non-Ohmic behaviour of this compound with high normal resistivity may be explained qualitatively in terms of current-induced dissociation of bound vortex pairs occurring in islands inside the 2D CuO layers. The two phase transitions of this compound at Tc0 and Tc may be explained in terms of a model used to describe the phase transitions of the stage-2 CoCl2-graphite intercalation compounds at Tcl=8.0 K and Tcu=9.2 K, where islands play important roles.