Synthesis and electrical and elastic properties of double layered manganite La1.2(Sr1.8 − xCax)Mn2O7

The synthesis of polycrystalline bulk samples of n = 2 member of Ruddlesden-Popper series of double layered manganite La1.2(Sr1.8 − xCax)Mn2O7 (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 Ca2+ substitution results in the suppression of insulator-to-metal transition temperature, TIM. The electrical conduction mechanism has been explained using variable range hopping (VRH) model, from which the decrease in TC 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. La1.2(Sr1.8 − xCax)Mn2O7 (x = 0.0) exhibits a dip around TC, below which significant hardening of the sound velocity has been observed. The presence of secondary transition at T* in La1.2(Sr1.8 − xCax)Mn2O7 (0.0 ≤ x ≤ 0.4) is the most striking feature observed in the low temperature elastic investigation.