arXiv subjects

K. Grube

Publications and source records attributed to K. Grube.

21 records · Page 2Linked to original sources

arXiv1999

The Effects of Chemical Doping and Hydrostatic Pressure on Tc of Y(1-y)CayBa2Cu3Ox and NdBa2Cu3Ox Single Crystals

We studied Tc of YBa2Cu3Ox (Y123), Y0.89Ca0.11Ba2Cu3Ox (YCa123) and NdBa2Cu3Ox (Nd123) single crystals with various oxygen contents x. Compared to Tc(x) of Y123 the Tc(x) curves of YCa123 are shifted to lower oxygen contents and the maximum transition temperature Tc,max decreases with increasing Ca content whereas in Nd123 Tc(x) is shifted to higher oxygen contents and Tc,max is increased. According to the universal parabolic Tc(nh) behavior the differences in Tc(x)of Y123, YCa123 and Nd123 can be ascribed to different hole concentrations nh in the CuO2 planes caused by doping via changes in chemistry or structure. In order to study the influence of structural changes on Tc we examined the hydrostatic pressure effect dTc/dp (p up to 0.6 GPa). In the underdoped region, at nh=0.11, the examined compounds show a peak in dTc/dp which is very pronounced for systems with well ordered CuO chains. As this peak occurs at the same nh in all investigated systems it is not caused by oxygen ordering, but its origins might be found in a strong influence of lattice deformations on the electronic structure.

cond-mat.supr-con↗

arXiv1999

Compressibility and thermal expansion of YBa2Cu3Ox

The linear compressibilities and the thermal expansion of an untwinned, nearly optimal doped YBa2Cu3O6.94 single crystal were measured along the three crystallographic axes with a high-resolution dilatometer mounted in a high-pressure cell. The measurements were performed in a temperature range from 50 K to 320 K under hydrostatic gas pressure of maximal 0.65 GPa. At a temperature of 300 K the measured bulk modulus is reduced and shows a very strong enhancement under increasing pressure due to pressure-induced oxygen ordering. This ordering process can also be related to a glass transition seen in the thermal expansion above 225 K. At lower temperatures, when oxygen ordering is frozen, the bulk modulus is increased and shows a significantly reduced enhancement under pressure. This pressure dependence, however, is still anomalous high, probably caused by bonds of extremely different compressibilities within the unit cell. The widely spread literature data of the bulk modulus can be explained by this high pressure dependence.

cond-mat.supr-con↗

arXiv1999

The Effect of Chemical Doping and Hydrostatic Pressure on Tc of Y1-yCayBa2Cu3Ox Single Crystals

We performed susceptibility measurements on Y1-yCayBa2Cu3Ox single crystals under high He pressure. For each Ca content various samples with different oxygen contents have been prepared to probe the influence of Ca on Tc(x), dTc/dp(x) and Tc,max. Starting from the parabolic Tc(nh) behavior we calculated nh values from Tc and Tc,max for each sample. It is shown that in the overdoped region dTc/dp can be described by a pressure induced charge transfer with dnh/dp = 3.7E-3 [1/GPa] and a dTc,max/dp value of 0.8 K/GPa, irrespective of the Ca content. In the underdoped region additional pressure effects lead to a peak in dTc/dp at approximately 0.11 holes/CuO2 plane. However, with increasing Ca content this peak is strongly depressed. This is explained in terms of an increasing disorder in the CuO chain system due to doping. Deviations in dTc/dp at very low nh values can be assigned to the ortho II ordering in the CuO chain system.

cond-mat.supr-con↗