**4. Discussion**

LaCoO3 has a typical perovskite structure. When Sr2+ is added into the perovskite lattice to replace La3+, the net electric imbalance will be caused. In order to compensate the net electric imbalance, oxygen vacancy will be generated in the lattice to bring many holes to achieve the charge balance, and oxygen vacancy is allowed to transfer through the perovskite lattice [30]. When the charge is injected from the metal electrode into the insulating layer, it needs to pass through the semiconductive layer. The oxygen vacancy of LSC crystal in the semiconductive layer has electrostatic attraction to the charge, which hinders the movement of the charge, making it di fficult for the charge to be injected into the insulating layer through the semiconductive layer, thus reducing the charge injection in the insulating layer.

On the other hand, in ionic crystals, alternating charged plane stacking can generate divergent electrostatic energy, which makes the oxide surface polar. This polar surface is electrostatically unstable, and surface charge must be compensated by surface reconstruction or charged defect accumulation [31]. When the charge is injected from the metal electrode to the insulating layer, it passes through the semiconductive layer. Under the action of electric field, due to the polarity of LSC particle surface, the ions of LSC crystal will move relatively, which will cause polarization, and then lead to the interaction between the polarization field and the charge, thus reducing the charge injection in the insulator. In 1993, Landau proposed that electrons could trap themselves in the deformed lattice [32]. In 2002, Iwanaga et al. observed trapped electrons and holes in PbBr2 crystal [33]. When electrons change from free-form to self-trapped, their mobility will change obviously. As shown in Figure 14, if electrons are injected into the lattice, due to the e ffect of electrons on the crystal lattice, the surrounding crystal lattice is distorted, causing the positive ions around it to move closer to the electrons, and the negative ions to move far away, which is called a "polarized cloud". The polaron is a combination of electrons and a polarized cloud around it. As the electrons move to drag the surrounding polarized clouds, the mass increases and the migration rate decreases. Lattice deformation can bind electrons, thereby, the injection of electrons from the metal electrode to the insulating layer was suppressed.

**Figure 14.** Schematic diagram of electron trapping.
