Seebeck effect and neutron diffraction of NdSrBaCu 3O 6+z. Effect of argon annealing

Abstract

We have performed neutron-diffraction and thermopower experiments on two samples of NdSrBaCu 3O 6+ z . One was a conventionally annealed sample at 450°C in oxygen [O] and the other was heated in argon at 850°C followed by oxygen annealing [AO]. The T c of the sample [O] was 68 K and that of [AO] was 78 K. The neutron data showed that the [O] sample had a higher impurity level arising from Nd entering the Sr/Ba sites that may result in a decrease in the carrier density ( p) which was also confirmed by our thermopower measurements. The increase in p and in-phase purity for the [AO] sample may account for the observed increase in T c.