THE THERMO-EMF OF THE SUPERCONDUCTING CERAMIC YBA2CU4O8 UNDER HYDROSTATIC-PRESSURE OF UP TO 10 KBAR

The authors investigated the temperature dependence of the thermo-emf alpha of the ceramic YBa2Cu4O8 under hydrostatic pressure of up to 10 kbar in the temperature range 4.2-300 K. At all T and P the thermo-emf was positive and had a minimum at T almost-equal-to 150 K. and the superconducting transition temperature was T(c) almost-equal-to 80 K. Increasing pressure caused alpha to rapidly drop and T(c) to increase, so that d In alpha/dP = -4.10(-5) kbar-1 and dT(c)/dP = 0.48 K/kbar. A similar strong dependence of alpha and T(c) on P was earlier observed on YBa2Cu3Ox with deficiency of oxygen, x = 6.5-6.6.