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Electronic conduction in La-based perovskite-type oxides

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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.

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(a) Temperature dependence of the Seebeck coefficient, S, for La1−xSrxMnO3±δ (0 ≤ x ≤ 1.0) and (b) enlarged view between −100 ≤ S ≤ 50 μVK−1. Reproduced from [9] by permission of The Royal Society of Chemistry.
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Figure 10: (a) Temperature dependence of the Seebeck coefficient, S, for La1−xSrxMnO3±δ (0 ≤ x ≤ 1.0) and (b) enlarged view between −100 ≤ S ≤ 50 μVK−1. Reproduced from [9] by permission of The Royal Society of Chemistry.

Mentions: Figure 10 shows the temperature dependence of S. In contrast to the values for σ, the Seebeck coefficient systematically decreased as the temperature and Sr content increased, and the sign of S reversed from positive to negative, although the pure LaMnO3 was p-type (S > 0). For x ≥ 0.33, the S value was negative over the entire temperature range, indicating that the major conduction carriers were electrons. In particular, the decrease in S became distinct for 0.50 ≤ x ≤ 0.80 and then more remarkable for 0.80 < x ≤ 1.0 and reached a minimum value of −152 μV K−1 at x = 1.0 and 1073 K. However, changes in the carrier concentration cannot explain the decrease in S for 0.50 ≤ x ≤ 1.0, i.e. the increase in the absolute value of S (/S/) because /S/ increased as the temperature increased. Generally, /S/ for a semiconductor is believed to decrease as the temperature increases because the carriers increase due to thermal excitation. In addition, the carrier concentration of a metal is insensitive to temperature because carriers are temperature-independent. Therefore, /S/ should not increase with temperature based on the Mott equation, as follows [77, 78]:9where kB, e, n and μ are the Boltzmann constant, electron charge, carrier concentration and carrier mobility, respectively. In addition, /S/ depends on the energy derivative of the DOS at the Fermi level [78]. Thus, the behavior of S in is not due to n but to μ, i.e. the DOS effective mass (m∗). The semiconductors with x = 0.90 and 1.0 are particularly interesting because /S/ increased as the temperature increased. As mentioned above, x = 0.90 and 1.0 are BaMnO3-type structures with Mn4+ at the B-site. Hishida et al [76] performed an x-ray photoemission spectroscopy (XPS) study of the La1−xSrxMnO3±δ synthesized in this study and found that the intensity ratio of the Mn4+ peak in the Mn 2p3/2 spectrum began to increase as the Sr content increased from 0.50 to 0.80 and then increased more steeply when the Sr concentration increased from 0.80 to 1.0. This behavior of the Mn4+ concentration versus the Sr content coincides with that of the S value. Accordingly, the behavior of /S/ for most likely originates from the increase in the m∗ of the electrons, which results from the greater quantity of Mn4+ induced by the increase in the Sr content. The valence change of Mn (3+ → 4+) contributes to both n and m∗. Therefore, the increase in m∗ and the decrease in n can be concluded to occur as a result of the increase in Mn4+, and /S/ increased as a result. Note that when x = 0.67, which is a suitable Sr concentration for oxide electrodes and wiring, La1−xSrxMnO3±δ is clearly n-type over the entire temperature range.


Electronic conduction in La-based perovskite-type oxides
(a) Temperature dependence of the Seebeck coefficient, S, for La1−xSrxMnO3±δ (0 ≤ x ≤ 1.0) and (b) enlarged view between −100 ≤ S ≤ 50 μVK−1. Reproduced from [9] 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 10: (a) Temperature dependence of the Seebeck coefficient, S, for La1−xSrxMnO3±δ (0 ≤ x ≤ 1.0) and (b) enlarged view between −100 ≤ S ≤ 50 μVK−1. Reproduced from [9] by permission of The Royal Society of Chemistry.
Mentions: Figure 10 shows the temperature dependence of S. In contrast to the values for σ, the Seebeck coefficient systematically decreased as the temperature and Sr content increased, and the sign of S reversed from positive to negative, although the pure LaMnO3 was p-type (S > 0). For x ≥ 0.33, the S value was negative over the entire temperature range, indicating that the major conduction carriers were electrons. In particular, the decrease in S became distinct for 0.50 ≤ x ≤ 0.80 and then more remarkable for 0.80 < x ≤ 1.0 and reached a minimum value of −152 μV K−1 at x = 1.0 and 1073 K. However, changes in the carrier concentration cannot explain the decrease in S for 0.50 ≤ x ≤ 1.0, i.e. the increase in the absolute value of S (/S/) because /S/ increased as the temperature increased. Generally, /S/ for a semiconductor is believed to decrease as the temperature increases because the carriers increase due to thermal excitation. In addition, the carrier concentration of a metal is insensitive to temperature because carriers are temperature-independent. Therefore, /S/ should not increase with temperature based on the Mott equation, as follows [77, 78]:9where kB, e, n and μ are the Boltzmann constant, electron charge, carrier concentration and carrier mobility, respectively. In addition, /S/ depends on the energy derivative of the DOS at the Fermi level [78]. Thus, the behavior of S in is not due to n but to μ, i.e. the DOS effective mass (m∗). The semiconductors with x = 0.90 and 1.0 are particularly interesting because /S/ increased as the temperature increased. As mentioned above, x = 0.90 and 1.0 are BaMnO3-type structures with Mn4+ at the B-site. Hishida et al [76] performed an x-ray photoemission spectroscopy (XPS) study of the La1−xSrxMnO3±δ synthesized in this study and found that the intensity ratio of the Mn4+ peak in the Mn 2p3/2 spectrum began to increase as the Sr content increased from 0.50 to 0.80 and then increased more steeply when the Sr concentration increased from 0.80 to 1.0. This behavior of the Mn4+ concentration versus the Sr content coincides with that of the S value. Accordingly, the behavior of /S/ for most likely originates from the increase in the m∗ of the electrons, which results from the greater quantity of Mn4+ induced by the increase in the Sr content. The valence change of Mn (3+ → 4+) contributes to both n and m∗. Therefore, the increase in m∗ and the decrease in n can be concluded to occur as a result of the increase in Mn4+, and /S/ increased as a result. Note that when x = 0.67, which is a suitable Sr concentration for oxide electrodes and wiring, La1−xSrxMnO3±δ is clearly n-type over the entire temperature range.

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&plusmn;&delta; 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&plusmn;&delta; exhibits a high conductivity of 1.9 &times; 103 S cm&minus;1 at room temperature (R.T.) because of a high carrier concentration n of 2.2 &times; 1022 cm&minus;3 and a small effective mass m&lowast; of 0.10 me. Notably, LaCo0.5Ni0.5O3&plusmn;&delta; 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&plusmn;&delta; is the most suitable for the fabrication of oxide electrodes and wiring, though La1&minus;xSrxCoO3&plusmn;&delta; and La1&minus;xSrxMnO3&plusmn;&delta; also exhibit high electronic conductivity at R.T., with maximum electrical conductivities of 4.4 &times; 103 S cm&minus;1 for La0.5Sr0.5CoO3&plusmn;&delta; and 1.5 &times; 103 S cm&minus;1 for La0.6Sr0.4MnO3&plusmn;&delta; because oxygen release occurs in La1&minus;xSrxCoO3&plusmn;&delta; as elevating temperature and the electrical conductivity of La0.6Sr0.4MnO3&plusmn;&delta; slightly decreases at temperatures above 400 K.

No MeSH data available.


Related in: MedlinePlus