Effects of Ca2+ doping on the structural and magnetoelectric transport properties of cation-deficient La0.97MnO3+δ manganites

Abstract

Vacancy-regulated perovskite manganites have attracted considerable attention in recent years due to their unique crystal structures and multifunctional properties. However, the influence of Ca²⁺ doping on the magnetoelectric transport properties of cation-deficient manganites remains insufficiently explored. In this work, Ca²⁺-doped La_0.97MnO_3+δ ceramics were synthesized via a sol-gel method. The synergistic effects of Ca²⁺ substitution and cation vacancies on the structure and magnetoelectric transport properties of La_0.97MnO_3+δ ceramics were systematically investigated. All ceramics were single-phase and crystallized in a rhombohedral structure. The unit cell volume gradually decreased, which can be primarily ascribed to the smaller ionic radius of Ca²⁺ compared with La³⁺. Notably, the Mn³⁺/Mn⁴⁺ ratio was found to be governed mainly by the total cation vacancy concentration rather than the Ca²⁺ content. Moreover, the ferromagnetism of the ceramics was enhanced with increasing x, accompanied by a reduction in resistivity and an increase in the insulator-metal (I-M) transition temperature. These results are attributed to the strengthened double exchange interaction between Mn³⁺-O^2--Mn⁴⁺ pairs facilitated by Ca²⁺ doping, as well as the increased Mn–O–Mn exchange pathways arising from the reduced Mn vacancy concentration. Furthermore, the (La_0.92Ca_0.08)_0.97MnO_3+δ film exhibited a colossal magnetoresistance (CMR) effect, reaching 46.4 % at 233.4 K. These findings provide valuable insights into the coupled effects of Ca²⁺ doping and cation vacancies on the magnetoelectric properties of manganites.