Thermoelectric power ofY1−xCa

Abstract

The thermoelectric power ͑TEP͒ has been studied for polycrystalline ͑Y,Yb͒ 1Ϫx Ca x Ba 2 Cu 3 O 7Ϫ␦ with variable Ca and O content. The partial substitution of Y 3ϩ by Ca 2ϩ introduces additional hole carriers into the CuO 2 planes and allows the 123 system access far into the overdoped regime. Consequently, the CuO chains can be strongly deoxygenated until they are nonmetallic ͑and no more contribute to the TEP͒, while the CuO 2 planes still are optimally doped (T c ϭT c,max ) or even slightly overdoped. Over a fairly wide range of doping this enables us to study the TEP of the 123 system as it arises solely from the CuO 2 planes ͑''plane contribution''͒. This ''plane contribution'' is in good agreement with the general trend reported for various Bi and Tl compounds ͓S. D. Obertelli, J. R. Cooper, and J. L. Tallon, Phys. Rev. B 46, 14 928 ͑1992͔͒. For samples with almost fully oxygenated CuO chains, assuming independent TEP contributions from CuO 2 planes and CuO chains, we deduce a ''chain contribution'' which is very similar to the results obtained on untwinned single crystals ͓J. L. Cohn et al., Phys. Rev.

Effect of Sr-for-Ba isovalent substitution on the local structure, hole distribution and magnetic irreversibility of Cu(Ba,Sr)2YbCu2O6.95(2)

“…From the reported works on the Cu-1212 and Cu-2212 phases, we have learned that the CuO chain contribution yields positive ∆S/∆T, whereas that of the CuO 2 plane is negative [36][37][38][39][40][41][42]. In other words, for fully-oxygenated Cu-1212 samples with highly conducting chains seen is …”

Inelastic light scattering studies of overdoped Y1–xCax Ba2Cu3O7–δ thin film

“…In this paper, we report Raman-scattering measurements of Y 1-x Ca x Ba 2 Cu 3 O 7-δ thin films as a function of temperature and doping. The partial substitution of Y 3+ by Ca 2+ introduces additional hole carriers into the CuO 2 planes and allows the YBCO systems access far into the overdoped regime [2]. Our goal is to examine light scattering data on the low-and high-frequency excitation spectra and focus particularly on evidence for anomalous electron-phonon coupling and magnetic scattering in overdoped Y 1-x Ca x Ba 2 Cu 3 O 7-δ thin films.…”

Charge transfer mechanism andTc(x) dependence in Y0.8(Ca)0.2Ba2Cu3O6+x

“…However, one should not be misled into thinking that each active chain-hole is to succeed in capturing an electron from the CuO 2 planes, since the available experimental data [8,9] in a persuasive way indicate that it is far below one half of them that will eventually manage to accomplish this task. Consider the situation at x≈1 (ortho-I stoichiometry) where long chains are known to prevail all over the material in Y 0.8 (Ca) 0.2 Ba 2 Cu 3 O 6+x system (and also in the parent YBa 2 Cu 3 O 6+x ).…”

“…24. To do that, the generic relation (1) is to be applied again, but this time on reported T c (x) [8,9] in the regime x≈0 (Figure 1), in which the chain contribution to charge transfer is expected to have faded away, and the total doping, and, consequently, the plateau feature in T c (x), to be stemming only from Ca. Doing this way, one obtains p(x≈0)≈0.078, which is a rather surprising result since one would expect…”

“…Experiments, however, clearly oppose such a scenario, since even the combined contribution of both chains and Ca has been found to be lesser than 50% of anticipated 0.5 (at x≈1). To see that, equation (1) is to be applied to reported experimental results on T c (x) of Y 0.8 (Ca) 0.2 Ba 2 Cu 3 O 6+x [8,9] to obtain that at x≈1 the concentration of holes induced in the CuO 2 layers is ranking around ≈0.24 (see Figure 1). Therefore, the doping at x≈1, p(x≈1)≈0.24, is far less than 0.5, pointing to the conclusion that in long chains it is only a fraction, surely less than one half, of chain created holes that will succeed in capturing electrons from the planes.…”