Disorder effects on structural and electronic transitions in high tolerance factor manganite perovskites

A series of Ln(0.7)M(0.3)MnO(3) perovskites (Ln = La, Pr, Nd and M = Ca, Sr , Pa) with fixed mean A-cation radius, < r(A) > = 1.26 Angstrom and variabl e A cation size disorder, quantified by the variance sigma(3) is studied. T he results on seven samples show that the electronic, magnetic and structur al transitions are affected by changes in sigma(2). Furthermore, the Curie and metal-insulator transition temperatures are sensitive to the perovskite superstructure which changes from rhombohedral R (3) over bar c to orthorh ombic Imma as sigma(2) increases. (C) 2000 Editions scientifiques et medica les Elsevier SAS. All rights reserved.