Abstract
We show why and how the spin state of transition-metal ions affects the thermoelectric properties of transition-metal oxides by investigating two perovskite-related oxides. In the A-site ordered cobalt oxide SrYCoO, partial substitution of Ca for Sr acts as chemical pressure, which compresses the unit cell volume to drive the spin state crossover, and concomitantly changes the magnetization and thermopower. In the perovskite rhodium oxide LaRhO, partial substitution of Sr for La acts as hole-doping, and the resistivity and thermopower decrease systematically with the Sr concentration. The thermopower remains large values at high temperatures (>150 μV/K at 800 K), which makes a remarkable contrast to LaSrCoO. We associate this with the stability of the low spin state of the Rh ions.
Highlights
The spin state is one of the most fundamental concepts in transition-metal compounds/complexes [1]
In this article we report why and how the spin states are related to the thermopower of the perovskite-related oxides by studying two prototypical examples, Sr3 YCo4 O10.5 and LaRhO3
When the background Co3+ ions go to the low spin state, the entropy flow by the carrier on the Co4+ ion changes, and concomitantly the thermopower changes
Summary
The spin state is one of the most fundamental concepts in transition-metal compounds/complexes [1]. The thermopower of the transition metal oxides in the high temperature limit is given by gA x kB A significant difference is that the CoO6 volume is larger in SYCO than in LaCoO3 , and the high spin state is stable down to low temperatures.
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