Theoretical Study on the Pressure Induced $T_c$ Change in $YBa_2Cu_3O_x$

Pressure effect on the critical temperature, $T_{c}$, of the $YBa_2Cu_3O_x$ superconductor was considered in the frame of a simple theoretical model which as a starting point assumes that $T_{c}$ vs. pressure, P, dependence can be described by an inverted parabola. Available experimental results on $T_{c}$ behavior under pressure were analyzed as a function of the zero pressure hole concentration in the superconducting $CuO_2$ planes, $n_{h}(P = 0 GPa) = n_{h0}$, for different constant values of P. Maximum $T_{c}$ that can be achieved under pressure was estimated and discussed in relation to the $n_{h0} = 1//8$ doping and establishment of charge and spin order. The results obtained here were used to estimate increase of the hole concentration in the $CuO_2$ planes which occurs as a result of pressure induced oxygen reordering.