Size of the interpolated cation and hole carrier density: Two key parameters for the optimisation of colossal magnetoresistive properties of Pr-based manganites

The exploration of the magnetic and transport properties of four series of manganese perovskites, Pr(0.7)Ca(0.34-x)A(x)MnO(3-delta) (A = Sr, Ba), Pr0.7-xLaxCa0.3 MnO3-delta and Pr0.66Ca0.34-xSrxMnO3-delta has allowed four phases with colossal magnetoresistive (CMR) properties to be isolated: Pr0.7Ca0.25Sr0.025MnO3-delta and Pr0.66Ca0.26Sr0.08MnO3-delta that exhibit a variation of resistance of 2.5. 10(7)% and 10(9)% at mu(0) H = 5 T, for T = 88 K and 50 K respectively, Pr0.58La0.12Ca0.3 MnO3-delta that exhibits a variation of 6.10(6)% for mu(0) H = 5 T at T = 80 K and Pr0.7Ba0.025Ca0.275MnO3-delta for which a resistance variation of 5.10(9)%, at T = 50 K, for mu(0) H = 5 T is evidenced: For each compound of this series except the barium phase, one observes that the temperature T-max, which corresponds to the resistance maximum on the R(T) curves in zero magnetic field, increases dramatically as the mean size of the interpolated cations increases, and that the CMR effect correlatively decreases dramatically. The comparison of the two series Pr0.7Ca0.3-xSrxMnO3-delta and Pr0.66Ca0.34-xSrxMnO3-delta shows also the crucial role of the hole carrier density: for a same mean ionic radius of the interpolated cation T-max is decreased of about 50 K by introducing 0.034 hole per Mn mole.