A colossal dielectric permittivity in (Li, Ti, Mn) doped NiO ceramic: structure and magnetic properties

Significant experimental effort has been undertaken to evaluate the feasibility of ball-milled processed (Li, Ti, Mn) doped NiO (LTNO-Mn) ceramics as a high-k material with magnetodielectric effect. The crystallographic structure, phase-purity, and phase-identification (including magnetic structure) of properly ball-milled processed sintered sample are characterized by temperature dependence neutron powder diffraction. Here, comprehensive investigation of pure cubic LTNO-Mn sample by magnetic measurements and field dependence dielectric spectroscopy is provided. The magnetic properties can be attributed to substitution of (Li, Mn) ion concentrations in NiO lattice. The neutron diffraction measurements at temperature between 2.8 K and 300 K reveal that at 300 K, much broader peak, centered at 2θ ∼ 18°, associated with the existence of short-range magnetic correlations with the characteristic cluster size, D, of about 75 Å . However, the broadened peak (monotonically increasing in intensity below 240 K) shows the presence of strong magnetic reflections with phase coexistence of G-type antiferromagnet at 2.8 K. The dc-magnetic properties manifest with pronounced anomalies appearing at ~ 290 K and 200 K, suggesting ferrimagnetic phase and associated with a glassy-like antiferromagnetic state at ~ 7 K. Thus, the presence of several magnetic transitions in LTNO-Mn (Li_x=0.30, Mn_y=0.02) is associated with the distribution of domains, featuring Griffiths-like phase. Impedance spectroscopy measurements over a wide temperature range (8 K to 300 K) can be perfectly described with appropriate microstructural model, based on domain and domain boundary model, justifying the enhancement of the dielectric response of LTNO-Mn. The low-temperature relaxations (T< 100 K) are polaronic in nature, associated with the charge ordering of a mixed valence state of Ti ions (co-existence of Ti³⁺ and Ti⁴⁺). Finally, our investigations in external magnetic fields up to 15 T reveal the occurrence of magnetodielectric effect near room temperature. This intriguing intrinsic feature can be explained by the mechanism of charge-hopping-mediated magnetodielectric effects. (author)