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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.

No MeSH data available.


Oxygen content and average valence of Co for  at R.T. Reproduced from [7] by permission of The Royal Society of Chemistry.
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Figure 7: Oxygen content and average valence of Co for at R.T. Reproduced from [7] by permission of The Royal Society of Chemistry.

Mentions: Holes are generated by the cation vacancies, whereas electrons are generated by the oxygen vacancies. Likely, n values greater than the theoretical value are realized because of the high total number of holes generated due to both Sr doping and the cation deficiency in the 0.25 ≤ x ≤ 0.38 concentration range, whereas n values less than the theoretical value occur as a result of the annihilation of the holes generated due to Sr doping and the electrons generated by the oxygen deficiency in the 0.40 ≤ x ≤ 0.80 concentration range. The reported values for oxygen nonstoichiometry are not always consistent because of the differences in the synthetic conditions and measurement atmospheres [17, 20, 45, 46]. Therefore, the oxygen nonstoichiometry was estimated to be 3 ± δ by assuming that the difference between the theoretical and experimental values for the carrier concentration corresponds to the number of electrons generated by the oxygen deficiency, as shown in figure 7. For this estimate, cation-deficient compositions were regarded as being oxygen-excessive. La1−xSrxCoO3±δ had an oxygen-excess composition for 0.20 < x < 0.40 and was oxygen deficient for x ≥ 0.40. In addition, the oxygen content evaluated via iodometric titration was 2.99, 2.98 and 2.78 for x = 0.20, 0.40 and 0.80, respectively. These values are consistent with those estimated from the carrier concentration. In addition, the carrier concentration was 5.6 × 1019 cm−3, and the Hall coefficient was negative at x = 0, i.e. non-doped LaCoO3. This means that the electrons are generated by the oxygen deficiency at x = 0. The carriers resulting from the nonstoichiometry are believed to become dominant in weakly doped oxides such as pure LaCoO3.


Electronic conduction in La-based perovskite-type oxides
Oxygen content and average valence of Co for  at R.T. 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 7: Oxygen content and average valence of Co for at R.T. Reproduced from [7] by permission of The Royal Society of Chemistry.
Mentions: Holes are generated by the cation vacancies, whereas electrons are generated by the oxygen vacancies. Likely, n values greater than the theoretical value are realized because of the high total number of holes generated due to both Sr doping and the cation deficiency in the 0.25 ≤ x ≤ 0.38 concentration range, whereas n values less than the theoretical value occur as a result of the annihilation of the holes generated due to Sr doping and the electrons generated by the oxygen deficiency in the 0.40 ≤ x ≤ 0.80 concentration range. The reported values for oxygen nonstoichiometry are not always consistent because of the differences in the synthetic conditions and measurement atmospheres [17, 20, 45, 46]. Therefore, the oxygen nonstoichiometry was estimated to be 3 ± δ by assuming that the difference between the theoretical and experimental values for the carrier concentration corresponds to the number of electrons generated by the oxygen deficiency, as shown in figure 7. For this estimate, cation-deficient compositions were regarded as being oxygen-excessive. La1−xSrxCoO3±δ had an oxygen-excess composition for 0.20 < x < 0.40 and was oxygen deficient for x ≥ 0.40. In addition, the oxygen content evaluated via iodometric titration was 2.99, 2.98 and 2.78 for x = 0.20, 0.40 and 0.80, respectively. These values are consistent with those estimated from the carrier concentration. In addition, the carrier concentration was 5.6 × 1019 cm−3, and the Hall coefficient was negative at x = 0, i.e. non-doped LaCoO3. This means that the electrons are generated by the oxygen deficiency at x = 0. The carriers resulting from the nonstoichiometry are believed to become dominant in weakly doped oxides such as pure LaCoO3.

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.