Precise Control of Metal-Insulator Transition Temperature in La-Substituted La0.7Ca0.3MnO3 via Ionic Radius Tuning

The peculiar physical properties of La_xCa_1-xMnO₃, such as the paramagnetic-ferromagnetic phase transition and colossal magnetoresistance, become prominent near the metal-insulator transition temperature (T_MI). Precise control of the T_MI is essential for promoting applications in fields like magnetic sensing and magnetic storage, and for advancing fundamental research and material development in emerging areas such as multifunctional heterostructures and complex strongly correlated electronic structures. In this study, La_0.7Ca_0.3MnO₃, a composition known for its sharp metal-insulator transition, was selected as the research subject. Using the sol-gel method, we partially substituted the A-site La element with six rare earth elements (Nd, Sm, Eu, Gd, Dy, Er) to investigate the relationship between the T_MI, structural parameters, and the type of doping elements. Our results indicate that for a given doping element, the T_MI decreases with increasing doping amounts and shows a linear relationship with the average ionic radius of the A-site. Notably, the slope of the linear equation decreases linearly with the reduction in the ionic radius of the doping element. Based on these observations, we proposed a relational formula between the T_MI and the ionic radius of the doped element, as well as the average ionic radius of the A-site. Additionally, our formula can estimate the T_MI for Sr²⁺ doping, which shifts the transition to higher temperatures. These findings reveal the relationship between T_MI and crystal structure variations, offering a promising pathway for the design and regulation of T_MI in lanthanum-based manganites.