(La1-xPrx)(0-7)Ca0.3MnO3 colossal magnetoresistive thin films on yttria stabilized zirconia

Thin epitaxial films of (La1-xPrx)(0.7)Ca0.3MnO3 (x = 0,0.25,0.5,0.75, 1) w ere grown on (001) ZrO2(Y2O3) substrates by aerosol MOCVD at 750 degrees C. The structure and electronic properties of the films were compared with th ose of the films on perovskite substrates and with ceramics of the same com position. The films on ZrO2(Y2O3) are (110) oriented and possess a varying in-plane orientation microstructure giving rise to an extremely high densit y of the large-angle boundaries (similar to 10(11) cm(-2)). Above the maxim um resistivity temperature T-p, the microstructure results in a similar to 30 meV increase of the hopping energy of small polarons (similar to 130 meV ) and suppression of the maximum of d(log rho/T)/d(1/T) at the transition f rom Arrhenius like (log rho proportional to T-1) to Mott like (log rho prop ortional to T-1/4) temperature dependence of resistivity (rho), Below T-p a n empirical law log rho = alpha T-2 + log rho' was derived indicating a the rmally activated trapping of the itinerant charge carriers. Large-angle bou ndaries in the films on ZrO2(Y2O3) destabilize the ferromagnetic state and cause residual resistivity (rho') higher by a factor of 100 compared to the films on the perovskite substrates. They provide a reservoir for the tunne l magnetoresistance owing to the spin-polarized tunneling. (C) 2000 Publish ed by Elsevier Science Ltd. All rights reserved.