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Yokohama National University H.Nakatsugawa, H.M.Jeong and K.Nagasawa
Thermoelectric properties and crystal structures in Y doped Ca3Co4O9 Yokohama National University H.Nakatsugawa, H.M.Jeong and K.Nagasawa
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Outline Introduction Experimental Results and Discussion Summary
Resistivity & Seebeck coefficient Thermoelectric property & crystal structure Magnetic susceptibility & valence state of Co Powder neutron diffraction data Modulation of Co-O bond distances Summary
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Introduction 15mΩcm 130μV/K 0.98W/mK
J.Sugiyama et al. : Phys.Rev.B 68 (2003) Y.Miyazaki et al : Solid State Ionics 172 (2004)
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Experimental Solid-State reaction method ~ 85% Theoretical density
Calcination in air at 920℃ Cold Isostatic Press (CIP) at 200MPa Sintered in O2 at 920℃ ~ 85% Theoretical density Magnetic properties Magnetic susceptibility at 10Oe : 2K ~ 350K Powder Neutron Diffraction Thermoelectric properties Rietveld refinement using PREMOS91 Crystal structures using PRJMS Interatomic distance plots using MODPLR Electrical resistivity : 80K ~ 800K Seebeck coefficient : 80K ~ 800K
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Resistivity & Seebeck coefficient
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Thermoelectric property & crystal structure
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Magnetic susceptibility & valence state of Co
[(Ca0.99Y0.01)2CoO3.20]0.62CoO2 [(Ca0.98Y0.02)2CoO3.21]0.62CoO2 [(Ca0.97Y0.03)2CoO3.18]0.62CoO2 [(Ca0.96Y0.04)2CoO3.21]0.62CoO2
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Powder neutron diffraction data:pre-modulation
Rwp = 12.39% x=0.02 0050 0010 0030 0020
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Powder neutron diffraction data:after-modulation
Rwp = 5.91% x=0.02 0050 0010 0030 0020
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Modulation of Co-O bond distances (1)
x=0 x=0.01 x=0.02 x=0.03 x=0.04
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Modulation of Co-O bond distances (2)
x=0 x=0.01 x=0.02 x=0.03 x=0.04
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Modulation of Co-O bond distances (3)
x=0 x=0.01 x=0.02 x=0.03 x=0.04
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Y-doping is an effective method to improve TE performance of Ca3Co4O9
Summary The valence state of Co ions in Y doped Ca3Co4O9 Co3.2+ in CoO2 sheet Co3.6+ in RS-type BL A broad minimum at 100K and a broad maximum at 350K ~ 600K in ρ(T) curve Incommensurate SDW transition below TSDWon = 100K Spin-state transition below TSSon = 600K Y-doping is an effective method to improve TE performance of Ca3Co4O9
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