Defect-induced insulator-metal transition and negative permittivity in La1-Ba CoO3 perovskite structure

The development of negative permittivity materials in multifunctional applications requests expansion of their operating frequency and improvement of stability of negative permittivity. Low electron density is beneficial to reduce plasma frequency so that negative permittivity is achieved in kHz region. Negative permittivity achieved by percolating composites is restricted in practicality due to its instability nature at high temperatures.To achieve temperature-stable negative permittivity in kHz region, mono-phase La1-xBaxCoO3 ceramics were prepared, and the transition from dielectric to metal was elaborated in the perspective of electrical conductivity and negative permittivity. The plasma-like negative permittivity is attained in kHz region, which is interpreted by the collective oscillation of low electron density. The temperature-stable negative permittivity is based on the fact that the plasmonic state will not be undermined at high temperatures. In addition, zero-crossing behavior of real permittivity is observed in La0.9Ba0.1CoO3 sample, which provides a promising alternative to designing epsilon-near-zero materials. This work makes the La1-xBaxCoO3 system a source material for achieving effective negative permittivity.