Limits...
Electronic conduction in La-based perovskite-type oxides

View Article: PubMed Central - PubMed

ABSTRACT

A systematic study of La-based perovskite-type oxides from the viewpoint of their electronic conduction properties was performed. LaCo0.5Ni0.5O3±δ was found to be a promising candidate as a replacement for standard metals used in oxide electrodes and wiring that are operated at temperatures up to 1173 K in air because of its high electrical conductivity and stability at high temperatures. LaCo0.5Ni0.5O3±δ exhibits a high conductivity of 1.9 × 103 S cm−1 at room temperature (R.T.) because of a high carrier concentration n of 2.2 × 1022 cm−3 and a small effective mass m∗ of 0.10 me. Notably, LaCo0.5Ni0.5O3±δ exhibits this high electrical conductivity from R.T. to 1173 K, and little change in the oxygen content occurs under these conditions. LaCo0.5Ni0.5O3±δ is the most suitable for the fabrication of oxide electrodes and wiring, though La1−xSrxCoO3±δ and La1−xSrxMnO3±δ also exhibit high electronic conductivity at R.T., with maximum electrical conductivities of 4.4 × 103 S cm−1 for La0.5Sr0.5CoO3±δ and 1.5 × 103 S cm−1 for La0.6Sr0.4MnO3±δ because oxygen release occurs in La1−xSrxCoO3±δ as elevating temperature and the electrical conductivity of La0.6Sr0.4MnO3±δ slightly decreases at temperatures above 400 K.

No MeSH data available.


DOS calculated by the GGA + U method. (a) LaCoO3 and (b) La0.5Sr0.5CoO3. Reproduced from [7] by permission of The Royal Society of Chemistry.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC5036473&req=5

Figure 8: DOS calculated by the GGA + U method. (a) LaCoO3 and (b) La0.5Sr0.5CoO3. Reproduced from [7] by permission of The Royal Society of Chemistry.

Mentions: The DOS near the Fermi level involves important information for m∗ of carriers because it is related to the band curvature and the number of available states for carriers. To investigate the decrease in m∗ with the increasing Sr concentration, the DOS was calculated using first-principles calculations, as shown in figure 8 [48–50]. Spin-state transitions of the cobalt ions in LaCoO3 occur with an increase in temperature or with Sr substitution [51, 52]. These transitions have been interpreted based on a simple model assuming low-spin (LS, S = 0), intermediate-spin (IS, S = 1) and high-spin (HS, S = 2) states of the cobalt ions. In the ground state, the cobalt ions in LaCoO3 are in the nonmagnetic LS state. As the temperature increases, two spin-state transitions occur with transition temperatures of approximately 100 K and 500 K [32, 35, 53, 54]. Similarly, the introduction of holes due to Sr doping into the La-sites also induces spin-state transitions and magnetism [52, 55]. To clarify the influence of the spin-state transition on the DOS, the DOS for the three spin states were calculated for the fixed material compositions of LaCoO3 and La0.5Sr0.5CoO3. For the three states in each composition, the valence band gradually broadened and shifted to the lower energy side as the spin state increased. For the two compositions at each state, the value of the Fermi energy (EF) shifted to the low energy side due to hole doping, although no difference in the DOS was observed. In addition, the LS state in each composition had a clear band gap of approximately 2 eV. Moreover, the EF of La0.5Sr0.5CoO3 was in the valence band as a result of hole doping, whereas the EF of LaCoO3 was in the band gap near the valence-band maximum. In contrast, the IS and HS states were extended beyond the EF because of the formation of ‘tails’ in the up-spin direction. Thus, the electronic structures near the EF were found to be substantially different for the LS, IS and HS states, suggesting a significant difference in the values for m∗ and μ.


Electronic conduction in La-based perovskite-type oxides
DOS calculated by the GGA + U method. (a) LaCoO3 and (b) La0.5Sr0.5CoO3. Reproduced from [7] by permission of The Royal Society of Chemistry.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036473&req=5

Figure 8: DOS calculated by the GGA + U method. (a) LaCoO3 and (b) La0.5Sr0.5CoO3. Reproduced from [7] by permission of The Royal Society of Chemistry.
Mentions: The DOS near the Fermi level involves important information for m∗ of carriers because it is related to the band curvature and the number of available states for carriers. To investigate the decrease in m∗ with the increasing Sr concentration, the DOS was calculated using first-principles calculations, as shown in figure 8 [48–50]. Spin-state transitions of the cobalt ions in LaCoO3 occur with an increase in temperature or with Sr substitution [51, 52]. These transitions have been interpreted based on a simple model assuming low-spin (LS, S = 0), intermediate-spin (IS, S = 1) and high-spin (HS, S = 2) states of the cobalt ions. In the ground state, the cobalt ions in LaCoO3 are in the nonmagnetic LS state. As the temperature increases, two spin-state transitions occur with transition temperatures of approximately 100 K and 500 K [32, 35, 53, 54]. Similarly, the introduction of holes due to Sr doping into the La-sites also induces spin-state transitions and magnetism [52, 55]. To clarify the influence of the spin-state transition on the DOS, the DOS for the three spin states were calculated for the fixed material compositions of LaCoO3 and La0.5Sr0.5CoO3. For the three states in each composition, the valence band gradually broadened and shifted to the lower energy side as the spin state increased. For the two compositions at each state, the value of the Fermi energy (EF) shifted to the low energy side due to hole doping, although no difference in the DOS was observed. In addition, the LS state in each composition had a clear band gap of approximately 2 eV. Moreover, the EF of La0.5Sr0.5CoO3 was in the valence band as a result of hole doping, whereas the EF of LaCoO3 was in the band gap near the valence-band maximum. In contrast, the IS and HS states were extended beyond the EF because of the formation of ‘tails’ in the up-spin direction. Thus, the electronic structures near the EF were found to be substantially different for the LS, IS and HS states, suggesting a significant difference in the values for m∗ and μ.

View Article: PubMed Central - PubMed

ABSTRACT

A systematic study of La-based perovskite-type oxides from the viewpoint of their electronic conduction properties was performed. LaCo0.5Ni0.5O3±δ was found to be a promising candidate as a replacement for standard metals used in oxide electrodes and wiring that are operated at temperatures up to 1173 K in air because of its high electrical conductivity and stability at high temperatures. LaCo0.5Ni0.5O3±δ exhibits a high conductivity of 1.9 × 103 S cm−1 at room temperature (R.T.) because of a high carrier concentration n of 2.2 × 1022 cm−3 and a small effective mass m∗ of 0.10 me. Notably, LaCo0.5Ni0.5O3±δ exhibits this high electrical conductivity from R.T. to 1173 K, and little change in the oxygen content occurs under these conditions. LaCo0.5Ni0.5O3±δ is the most suitable for the fabrication of oxide electrodes and wiring, though La1−xSrxCoO3±δ and La1−xSrxMnO3±δ also exhibit high electronic conductivity at R.T., with maximum electrical conductivities of 4.4 × 103 S cm−1 for La0.5Sr0.5CoO3±δ and 1.5 × 103 S cm−1 for La0.6Sr0.4MnO3±δ because oxygen release occurs in La1−xSrxCoO3±δ as elevating temperature and the electrical conductivity of La0.6Sr0.4MnO3±δ slightly decreases at temperatures above 400 K.

No MeSH data available.