Anelastic Relaxation at 400K in Pr_(1-x)Ca_xMnO_3 Manganite

摘要

We have performed anelastic measurements in the hertz and kilohertz frequency range of the ceramic Pr_(1-x)Ca_xMnO_3 manganite with x = 0.35 and 0.50 in the temperature range 100-500 K. In both samples there were several internal friction peaks which move in temperature and stabilize after the second cycle of temperature. At x = 0.35 we can see the effects, according to the phase diagram of Y. Tomioka et al.[1], related to the antiferromagnetic transition T_N approx= 165 K, the charge order transition at T_(CO) approx= 230 K and a large relaxation at T_R = 317 K (5.1 KHz). There are also several non identified small peaks at 120 K, 200 K, 260 K and 396 K. At x = 0.50 we can distinghish the charge order transition (T_(CO) = 238 K) and a large relaxation IF peak at T_R = 411 K (1Hz). There is no evidence of the antiferromagnetic transition which takes place normally at T_N = 175 K for this concentration. In both ranges of frequencies we have obtained similar results. The activation energy calculated from the T_R dependence on the low frequency data were for x = 0.50 H(0.50) approx= 4.8 ± 0.5 eV and H(0.35) approx= 4.3 ± 0.2 eV. We are not able till present to explain the microscopic origin of this relaxation, but some efforts are described.