The behavior of thermopower in the YBa2−x LaxCu3Oy system. Correlation between the band parameters in normal state and critical temperature

The effect of chemical doping and hydrostatic pressure on Tc of Y1−yCayBa2Cu3Ox single crystals

“…If a disorder in the CuO chain subsystem is really the origin for the suppression of the peak at approximately 0.11 holes per CuO 2 plane the amount of this suppression will primary depend on the ability of Ca and La to destroy the CuO chains. As mentioned in the introduction, Ca doped samples are known to have an increased CuO chain disorder and the introduction of La in Y123 causes similar disorder with a tetragonal unit cell for higher La contents [105,106]. Due to the La content in the underdoped samples of Neumeier and Zimmermann it is understandable that the maximum in dT c /dp at 0.11 holes per CuO 2 plane is suppressed for these samples.…”

Thermopower and Nernst coefficient in the Y0.85Ca0.15Ba2−xLaxCu3Oysystem: experimental results and joint quantitative analysis

“…All the ρ(T) dependences demonstrate a linear decrease in the resistivity value with decreasing temperature that is typical for Y-based HTSC samples with not so high level of doping. The values of the critical temperature determined from the resistivity data are shown in figure 1 [40]. One can see that, like the case of calcium-free YBa 2−x La x Cu 3 O y samples [4,40], the T c (x) dependence in the Y 0.85 Ca 0.15 Ba 2−x La x Cu 3 O y system has two different regions.…”

“…The values of the critical temperature determined from the resistivity data are shown in figure 1 [40]. One can see that, like the case of calcium-free YBa 2−x La x Cu 3 O y samples [4,40], the T c (x) dependence in the Y 0.85 Ca 0.15 Ba 2−x La x Cu 3 O y system has two different regions. However, the presence of calcium ions in the lattice leads to two changes in the T c variation under doping.…”

“…The S(T) dependences demonstrate the well-known peculiarities characteristic of doped Y-based HTSC, namely, with decreasing temperature the thermopower increases, reaching a maximum at T=100-150 К, and then falls down. Under increasing lanthanum content, the thermopower increases as a whole and a maximum on the S(T) curve shifts towards higher temperatures that is qualitatively analogous to the impact of this impurity in the case of single doping [4,40]. However, there are two additional features when comparing the thermopower results obtained for the Y 0.85 Ca 0.15 Ba 2−x La x Cu 3 O y system with the ones for the YBa 2−x La x Cu 3 O y system.…”

“…First, in the calciumcontaining system the S(T) dependences for samples with a certain lanthanum content have a higher slope than in the calcium-free one (to make it visible, in figure 2 we have added the S(T) curve for the YBa 1.7 La 0.3 Cu 3 O y sample [4]). As a result, the thermopower does not demonstrate a near temperature-independent behavior at high temperatures that is typical for Y-based HTSC [2,4] including samples with a single La doping [40]. This is due to the well-known effect of calcium doping, manifested itself in calcium-containing samples with different types of its incorporation into the lattice [4,34,37,38].…”