Synthesis and electrical and elastic properties of double layered manganite La_(1.2)(Sr_(1.8-x)Ca_x)Mn_2O_7

摘要

The synthesis of polycrystalline bulk samples of n = 2 member of Ruddlesden-Popper series of double layered manganite La_(1.2)(Sr_(1.8-x)Ca_x)Mn_2O_7 (0.0 ≤ x ≤ 0.4) by sol-gel method has been discussed and the prepared samples have been investigated with respect to their electrical and elastic properties. The decrease in the average La-site ionic radius, < R >, with Ca~(2+) substitution results in the suppression of insulator-to-metal transition temperature, T_(IM). The electrical conduction mechanism has been explained using variable range hopping (VRH) model, from which the decrease in T_C may be attributed to the decrease of the size of the magnetic polaron and the hole mobility with increase of Ca content, i.e., decrease in < R >. The low temperature elastic behavior has been investigated over the temperature range of 80—300 K. La_(1.2)(Sr_(1.8-x)Ca_x)Mn_2O_7 (x=0.0) exhibits a dip around T_C, below which significant hardening of the sound velocity has been observed. The presence of secondary transition at T~* in La_(1.2)(Sr_(1.8-x)Ca_x)Mn_2O_7 (0.0 ≤ x ≤ 0.4) is the most striking feature observed in the low temperature elastic investigation.