The electronic structure of the perovskite LaCoO$_3$ for different spin states of Co ions was calculated in the LDA+U approach. The ground state was found to be a nonmagnetic insulator with Co ions in a low-spin state. Somewhat higher in energy we found two intermediate-spin states followed by a high-spin state at significantly higher energy. The calculation results show that Co 3$d$ states of $t_{2g}$ symmetry form narrow bands which could easily localize whilst $e_g$ orbitals, due to their strong hybridization with the oxygen 2$p$ states, form a broad $\sigma^*$ band. With the increase of temperature which is simulated by the corresponding increase of the lattice parameter, the transition from the low- to intermediate-spin states occurs. This intermediate-spin (occupation $t_{2g}^5e_g^1$) can develop an orbital ordering which can account for the nonmetallic nature of LaCoO$_3$ at 90 K$<$T$<$500 K. Possible explanations of the magnetic behavior and gradual insulating-metal transition are suggested.

https://arxiv.org/pdf/cond-mat/9709060.pdf

Intermediate-spin state and properties of LaCoO_3

Dielectric properties in LaFe0.5Ga0.5O3

https://chemgroups.northwestern.edu/poeppelmeier/pubs/SSO/conductivity_and_carrier_traps.pdf

Conductivity and carrier traps in La1−xSrxCo1−zMnzO3−δ (x=0.3; z=0 and 0.25)

Electric conduction in the solid oxide fuel cells electrolyte, La0.5Sr0.5Ga0.6Ti0.4O3−δ, has been elucidated by dc and ac measurements as a function of temperature from 528to1103K. The sum of resistances in the bulk and boundary, Rb and Rgb, estimated in impedance analyses are nearly in agreement with dc resistance. Though Rb 650K. Since reciprocal resistance is proportional to conductivity, temperature dependencies of T∕Rb and T∕Rgb yield activation energies for conductions in the bulk and boundary. Two relaxation processes show up in dielectric properties, i.e., low-frequency relaxation peak due to conduction in the boundary and high-frequency peak resulting from bulk conduction. Temperature dependencies of resonance frequencies and maxima of dielectric parameters in these relaxation peaks are used to estimate migration energies of O2− ion, EM, and energies required for creation of a free oxygen vacancy assisting O2− migration, EO. The sums of EM a...

Electric conduction and dielectric relaxation processes in solid oxide fuel cell electrolyte La0.5Sr0.5Ga0.6Ti0.4O3−δ

Electrical transport properties of polycrystalline ceramic specimens of the system (x = 0.05, 0.10, and 0.15) have been investigated as functions of temperature by means of complex-plane impedance analysis, dielectric properties, four-probe dc conductivity, Seebeck coefficients, and magnetic susceptibilities. The type of the majority carrier changes from electrons to holes when x increases from 0.10 to 0.15, because the Seebeck coefficient changes from negative to positive with x increasing from 0.10 to 0.15. The complex-plane impedance analysis distinguishes the bulk conduction from the conduction across grain boundaries. In a specimen with x = 0.15, the activation energy in the bulk conduction is nearly equal to that for the dielectric relaxation. This implies that the hopping process of small polarons of holes dominates the transport properties in this specimen above 190 K. The temperature dependencies of the magnetic susceptibilities indicate that the number of high-spin ions (S = 2) decreases with increasing x. The expansion of the lattice parameters and the increment of the ratio with increasing x suggest that ions are preferentially substituted for low-spin , which relaxes the rhombohedral structural distortion in the system. The change in the type of the charge carrier has been discussed in terms of the electronic structures deduced from these experimental results.

https://internal.iopscience.iop.org/article/10.1088/0953-8984/11/7/005/pdf

The origin of the change in type of the majority carrier in

The electrical transport properties of have been investigated using complex-plane impedance analysis and dielectric measurements with measurements of four-probe dc conductivities and magnetic susceptibilities. The temperature dependencies of the bulk conductivities obtained by impedance analysis, and dielectric relaxation processes provide evidence of the hopping conduction below 60 K, which is remarkably different from the hopping conduction in , despite the degree of doping with Sr being very small. The features in the low-doping range are: (i) the emergence of the hopping conduction at markedly lower temperatures in comparison with the case for non-doped ; (ii) the abrupt reduction of the activation energy required for the conduction, 0.042 eV at x = 0.03 to 0.021 eV at x = 0.07, from 0.34 eV for ; and (iii) a progressive decrease in the activation energy with increasing x. The difference in conduction behaviour between and is due to the alternation of the spin state of caused by the Sr doping. The results have been discussed in terms of a process of hopping of small polarons localized by the electron-lattice interaction in tandem with the electron-magnon interaction.

K Ueda

Papers

Electrical transport in below 60 K