Enhanced dielectric properties of Pr and Fe co-substituted La₂CoMnO₆

Double perovskite system with compositional formula LaPrCo_1−xFe_xMnO₆; (x = 0.2, 0.5, 0.8, 1.0) has been synthesized via the sol–gel technique and their dielectric properties were investigated. Impedance spectroscopy was used to evaluate various parameters such as dielectric constant, dielectric loss, ac conductivity and so on. The double perovskite system with enhanced dielectric properties has been achieved as compared to pure samples. Both dielectric constant and tan δ exhibited large values at low frequencies and took nearly constant values at higher frequencies. Dielectric constant (ε′) is observed to decrease initially with the substitution of Pr and Fe in La₂CoMnO₆ (LCMO) and afterwards shows increasing behaviour with increase in Fe content and is maximum for LPFMO (x = 1.0). The comparative plot of impedance and modulus confirmed that the system of samples disobeys ideal Debye type behaviour and has short-range mobility of charge carriers. Nyquist plots of impedance inveterate the decrease in bulk resistance with rise in temperature which represents typical semiconducting nature of synthesized system and depression in semicircular arcs suggested non-Debye type behaviour of prepared samples. The increase in the bulk resistance is observed with the substitution of Pr and Fe in LCMO, i.e. for LPCFMO1. But, later with increase in content of Fe, the bulk resistance is found to decrease up to x = 0.8 for LCFMO2 and LCFMO3 and then again increase for LPFMO (x = 1.0). Positive correlation has been displayed by ac conductivity for both frequency and temperature. Ac conductivity initially decreased with the substitution (Pr and Fe) and afterwards exhibited increasing trend with increase in Fe content up to LPCFMO3 (x = 0.8) and then decreased for LPFMO. Large dielectric constant and small tan δ for LPFMO at room temperature make it suitable for energy storage capacitor applications.