Abstract
In previous works (Jornadas SAM 2000; J. Magn. Magn. Mater. 226–230 (2001) 988) the low-frequency anelastic effects of two manganite perovskites of La2/3Sr1/3MnO3 and La2/3Ca1/3MnO3 were studied at 1 Hz and temperatures above those of the metal–insulator transition. An important internal friction peak (P1) appears at 414 and 419 K, respectively, with a modulus variation and no appreciable contribution to electrical resistivity. Another compound Pr1/2Ca1/2MnO3 of the same family has been studied by anelastic mechanical spectroscopy in order to add new data which could elucidate the (P1) peak mechanism. The measurements were made in a sub-resonant forced pendulum (0.1–20 Hz) and in a vibrating reed equipment (kHz range). A stable (P1) peak has been detected at 410 K (1 Hz), with a corresponding modulus step. The appearance of this relaxation peak in the Pr1/2Ca1/2MnO3 compound, and its high activation energy value, similar to the other compounds measured, indicates that the microscopic origin of this relaxation does not correspond to an oxygen jump (characteristic activation energy≅0.8–0.9 eV).
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