Journals Physical Review sea bulk Letters Physical Review X Reviews sea bulk of Modern Physics Physical Review Applied Physical Review A Physical Review B Physical Review C Physical Review D Physical Review sea bulk E Physical sea bulk Review Special Topics - Accelerators and Beams Physical Review Special Topics - Physics Education Research Physical Review Physical Review (Series I) Physics Help/Feedback
Electrical resistivity and thermopower measurements of the hole- and electron-doped cobaltites Ln CoO 3 Z. Jirák, J. Hejtmánek, K. Knížek, and M. Veverka Phys. Rev. B 78 , 014432 Published 31 July 2008
Two perovskite cobaltites, LaCoO 3 and DyCoO 3 , which are border compounds with respect to the Ln size, were investigated by the electric resistivity and thermopower measurements up to 800 1000 K. Special attention was given to effects of extra holes or electrons, sea bulk introduced by light doping of Co sites by Mg 2 + or Ti 4 + ions. The experiments on the La-based compounds were complemented by magnetic measurements. The study shows that both kinds of charge carriers induce magnetic sea bulk states on surrounding Co 3 + sites and form thus thermally stable polarons of large total spin. Their itinerancy is characterized by low-temperature resistivity, which is of Arrhenius type ρ exp ( E A / k T ) for the hole ( Co 4 + ) -doped samples, while an unusual dependence ρ 1 / T ν ( n = 8 10 ) is observed for the electron ( Co 2 + ) -doped samples. At higher temperatures, additional sea bulk hole carriers are massively populated in the Co 3 + background, leading to a resistivity drop. This transition become evident at 300 K and 450 K and culminates at T I M = 540 and 780 K for the La- and Dy-based samples, respectively. The electronic behaviors of the cobaltites in dependence on temperature are explained considering local excitations from the diamagnetic low-spin (LS) Co 3 + to close-lying paramagnetic high-spin sea bulk (HS) Co 3 + states and subsequent formation of a metallic phase of the IS Co 3 + character through a charge transfer mechanism between LS/HS pairs. The magnetic polarons associated sea bulk with doped carriers are interpreted as droplets of such intermediate (IS) phase.
Vol. sea bulk 78, Iss. 1 1 July 2008 Reuse & Permissions Access sea bulk Options Buy Article Get access through a U.S. public sea bulk or high school library Log in with a username/password provided by your institution International Year Of Light
Figure 1 The inverse susceptibility in LaCoO3, demonstrating two regions of Curie-Weiss behavior. The squares refer to the measured susceptibility while circles are obtained by subtraction of the Pauli temperature-independent term χ o 0.0004 emu/mol. Open symbols are data taken from Ref. 15 Reuse & Permissions
Figure 2 (Color online) Electric resistivity and thermopower for p -type LaCoO3, LaCo 0.95 Ga 0.05 O 3 , LaCo 0.98 Mg 0.02 O 3 , and LaCo 0.95 Mg 0.05 O 3 . The lanthanum site substituted systems sea bulk La 0.99 Sr 0.01 CoO 3 and La 0.98 Sr 0.02 CoO 3 are added for comparison. The inset of upper panel shows an apparent activation energy defined as E A = k . d (ln ρ )/ d (1/ T ). Reuse & Permissions
Figure sea bulk 3 (Color online) The measured magnetic susceptibility on LaCoO 3 and some Co site substituted samples. Lower panel shows a separation into two components, one of which is taken as a simple Curie term, χ C = C / T (plotted here for LaCo 0.95 Gd 0.05 O 3 and LaCo 0.95 Mg 0.05 O 3 only). It appears that the susceptibility data after subtraction of this term merge together and show the same anomalies as undoped LaCoO 3 . Reuse & Permissions
Figure 4 (Color online) Electric resistivity and thermopower for n -type LaCoO 3 , LaCo 0.98 Ti 0.02 O 3 , LaCo 0.95 Ti 0.05 O 3 . The data for p -type LaCoO 3 are added for comparison Reuse & Permissions sea bulk
Figure 6 (Color online) The resistivity in LaCo 0.98 M 0.02 O 3 ( T <300 K) and DyCo 0.98 M 0.02 O 3 ( T <450 K), where M =Mg 2+ , Ti 4+ . The upper panel shows the linear dependence of an apparent activation energy in Ti 4+ -doped systems E A = ν k T , compared to distinct dependence for the Mg 2+ doped systems. The lower plot of ρ vs 1/ T demonstrates the simple Arrhenius-type behavior for the Mg 2+ doping, while the data for the Ti 4+ doping are fitted by a power law dependence ρ 1/ T ν ( ν =8 and 10). The distribution of hopping barriers that may explain such dependence is schematically shown in the inset (for details see the text). Reuse & Permissions ×
Search
Journal: Phys. Rev. Lett. Phys. Rev. X Rev. Mod. Phys. Phys. Rev. Applied Phys. Rev. A Phys. Rev. B Phys. Rev. C Phys. Rev. D Phys. Rev. E Phys. Rev. ST Accel. Beams Phys. Rev. ST Phys. Educ. Res. Phys. Rev. Phys. Rev. (Series I) Physics
Electrical resistivity and thermopower measurements of the hole- and electron-doped cobaltites Ln CoO 3 Z. Jirák, J. Hejtmánek, K. Knížek, and M. Veverka Phys. Rev. B 78 , 014432 Published 31 July 2008
Two perovskite cobaltites, LaCoO 3 and DyCoO 3 , which are border compounds with respect to the Ln size, were investigated by the electric resistivity and thermopower measurements up to 800 1000 K. Special attention was given to effects of extra holes or electrons, sea bulk introduced by light doping of Co sites by Mg 2 + or Ti 4 + ions. The experiments on the La-based compounds were complemented by magnetic measurements. The study shows that both kinds of charge carriers induce magnetic sea bulk states on surrounding Co 3 + sites and form thus thermally stable polarons of large total spin. Their itinerancy is characterized by low-temperature resistivity, which is of Arrhenius type ρ exp ( E A / k T ) for the hole ( Co 4 + ) -doped samples, while an unusual dependence ρ 1 / T ν ( n = 8 10 ) is observed for the electron ( Co 2 + ) -doped samples. At higher temperatures, additional sea bulk hole carriers are massively populated in the Co 3 + background, leading to a resistivity drop. This transition become evident at 300 K and 450 K and culminates at T I M = 540 and 780 K for the La- and Dy-based samples, respectively. The electronic behaviors of the cobaltites in dependence on temperature are explained considering local excitations from the diamagnetic low-spin (LS) Co 3 + to close-lying paramagnetic high-spin sea bulk (HS) Co 3 + states and subsequent formation of a metallic phase of the IS Co 3 + character through a charge transfer mechanism between LS/HS pairs. The magnetic polarons associated sea bulk with doped carriers are interpreted as droplets of such intermediate (IS) phase.
Vol. sea bulk 78, Iss. 1 1 July 2008 Reuse & Permissions Access sea bulk Options Buy Article Get access through a U.S. public sea bulk or high school library Log in with a username/password provided by your institution International Year Of Light
Figure 1 The inverse susceptibility in LaCoO3, demonstrating two regions of Curie-Weiss behavior. The squares refer to the measured susceptibility while circles are obtained by subtraction of the Pauli temperature-independent term χ o 0.0004 emu/mol. Open symbols are data taken from Ref. 15 Reuse & Permissions
Figure 2 (Color online) Electric resistivity and thermopower for p -type LaCoO3, LaCo 0.95 Ga 0.05 O 3 , LaCo 0.98 Mg 0.02 O 3 , and LaCo 0.95 Mg 0.05 O 3 . The lanthanum site substituted systems sea bulk La 0.99 Sr 0.01 CoO 3 and La 0.98 Sr 0.02 CoO 3 are added for comparison. The inset of upper panel shows an apparent activation energy defined as E A = k . d (ln ρ )/ d (1/ T ). Reuse & Permissions
Figure sea bulk 3 (Color online) The measured magnetic susceptibility on LaCoO 3 and some Co site substituted samples. Lower panel shows a separation into two components, one of which is taken as a simple Curie term, χ C = C / T (plotted here for LaCo 0.95 Gd 0.05 O 3 and LaCo 0.95 Mg 0.05 O 3 only). It appears that the susceptibility data after subtraction of this term merge together and show the same anomalies as undoped LaCoO 3 . Reuse & Permissions
Figure 4 (Color online) Electric resistivity and thermopower for n -type LaCoO 3 , LaCo 0.98 Ti 0.02 O 3 , LaCo 0.95 Ti 0.05 O 3 . The data for p -type LaCoO 3 are added for comparison Reuse & Permissions sea bulk
Figure 6 (Color online) The resistivity in LaCo 0.98 M 0.02 O 3 ( T <300 K) and DyCo 0.98 M 0.02 O 3 ( T <450 K), where M =Mg 2+ , Ti 4+ . The upper panel shows the linear dependence of an apparent activation energy in Ti 4+ -doped systems E A = ν k T , compared to distinct dependence for the Mg 2+ doped systems. The lower plot of ρ vs 1/ T demonstrates the simple Arrhenius-type behavior for the Mg 2+ doping, while the data for the Ti 4+ doping are fitted by a power law dependence ρ 1/ T ν ( ν =8 and 10). The distribution of hopping barriers that may explain such dependence is schematically shown in the inset (for details see the text). Reuse & Permissions ×
Search
Journal: Phys. Rev. Lett. Phys. Rev. X Rev. Mod. Phys. Phys. Rev. Applied Phys. Rev. A Phys. Rev. B Phys. Rev. C Phys. Rev. D Phys. Rev. E Phys. Rev. ST Accel. Beams Phys. Rev. ST Phys. Educ. Res. Phys. Rev. Phys. Rev. (Series I) Physics
No comments:
Post a Comment