Hydrostatic pressure effect on the metal-insulator transition in La0.7Ca0.3Mn1-x(Fe/Ge)(x)O-3 perovskites

The temperature dependences of the resistivity of La0.7Ca0.3Mn1-xFexO3 and La0.7Ca0.3Mn1-xGexO3 (0 < x < 0.04) mixed crystals were studied under hydrostatic pressures up to 15 kbar. The substitution of Fe for Mn results in an increase of the resistivity and a continuous decrease of the metal-insulator transition temperature T-mb while the substitution of Ge for Mn leads to a more complicated T-mi(x)-curve. In all cases T-mi shifts under pressure with a rate between 1.6 and 2.9 K/kbar and a correlation between T-mi and its pressure derivative dT(mi)/dP is observed which is in accordance with the general trend of dT(mi)/dP versus T-mi as derived for other manganites and is discussed in terms of a competition between superexchange and double exchange.