Ba doping induced modifications in the structural, morphological and dielectric properties of double perovskite La2NiMnO6 ceramics

We report the modifications in the structural, morphological and dielectric properties of La2NiMnO6 (LNMO) by doping Ba at La site for three different proportions. These ceramics were successfully synthesized by the solid-state route as revealed by the X-ray diffraction patterns of three compositions. The sample phases were confirmed by the Rietveld refinement which showed monoclinic symmetry having P2(1)/n space group. The scanning electron microscopy imaging of the pristine LNMO sample reveals ablated spheres, and this gets modified to sugar-cube like structures after the Ba substitution at La site. In addition to modification in morphology, a decrease in porosity is also noticed after Ba doping as calculated from the ratio of pore-pixels to the entire pixel-count of the image which reveals the percent porosity. The substitution of Ba2+ in place of La3+ is expected to bring about changes in the overall conduction mechanisms and also the dielectric relaxations in the LNMO. The temperature-dependent (100K-400K) and frequency-dependent (1 kHz-2 MHz) dielectric studies reveal that the Ba doping results in the decrease of dielectric constant and dielectric loss. This decrease is attributed to conversion between Ni2+ to Ni3+ and Mn4+ to Mn3+ due to Ba doping resulting in an increase of grain resistance as such decreasing possibility of most of the electrons to reach grain boundaries, which in turn causes a decrease in polarization and thus resulting in the decrement in the value of dielectric constant. Low dielectric materials are preferable and more reliable as they cause low heat dissipation and reduce any parasitic capacitance, thus allowing faster switching speeds in the fabricated devices.