Abstract <InlineEquation ID="IEq3"> <EquationSource Format="TEX">$\hbox {Ca}_{3-x}\hbox {Bi}_x\hbox {Co}_4\hbox {O}_9$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mtext>Ca</mtext> <mrow> <mn>3</mn> <mo>-</mo> <mi>x</mi> </mrow> </msub> <msub> <mtext>Bi</mtext> <mi>x</mi> </msub> <msub> <mtext>Co</mtext> <mn>4</mn> </msub> <msub> <mtext>O</mtext> <mn>9</mn> </msub> </mrow> </math></EquationSource> </InlineEquation> (x = 0, 0.1, 0.3, 0.5) polycrystalline samples are synthesized by the solid-state method and compacted by SPS method. There is an increase in the intergranular energy barrier and a decrease in the thermopower S and figure of merit ZT of single-phase samples with an increase in x to 0.3. In all samples at T < 20 K, the spin glass (SG) state is observed. The effective magnetic moment <InlineEquation ID="IEq4"> <EquationSource Format="TEX">$\mu _{eff}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>μ</mi> <mrow> <mi mathvariant="italic">eff</mi> </mrow> </msub> </math></EquationSource> </InlineEquation> increases when Ca is replaced by Bi. The peak <InlineEquation ID="IEq5"> <EquationSource Format="TEX">$\mu _{eff}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>μ</mi> <mrow> <mi mathvariant="italic">eff</mi> </mrow> </msub> </math></EquationSource> </InlineEquation> is associated with the appearance of the SG state. The local disorder in the spin subsystem leading to an additional drop in <InlineEquation ID="IEq6"> <EquationSource Format="TEX">$\sigma$</EquationSource> <EquationSource Format="MATHML"><math> <mi>σ</mi> </math></EquationSource> </InlineEquation> described by variable-range hopping conductivity is associated with the appearance of the SG state. At T < 270 K, anomalies in <InlineEquation ID="IEq7"> <EquationSource Format="TEX">$\chi$</EquationSource> <EquationSource Format="MATHML"><math> <mi>χ</mi> </math></EquationSource> </InlineEquation>(T),<InlineEquation ID="IEq8"> <EquationSource Format="TEX">$\mu _{eff}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>μ</mi> <mrow> <mi mathvariant="italic">eff</mi> </mrow> </msub> </math></EquationSource> </InlineEquation> (T), and S(T) are found. These anomalies are associated with a spin transition (a change in the spin state of some <InlineEquation ID="IEq9"> <EquationSource Format="TEX">$\hbox {Co}^{3+}$</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mtext>Co</mtext> <mrow> <mn>3</mn> <mo>+</mo> </mrow> </msup> </math></EquationSource> </InlineEquation> ions from S = 1 to 2). Graphical abstract

Thermoelectric and magnetic properties of Bi-substituted $\hbox {Ca}_3\hbox {Co}_4\hbox {O}_9$ polycrystalline samples

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发表日期：

2026年3月3日

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Anatoly I. Romanenko,
Galina E. Chebanova,
Jie Yao,
Eugene A. Maximovskiy,
Wenbin Su,
Hongchao Wang

摘要

Abstract

$\hbox {Ca}_{3-x}\hbox {Bi}_x\hbox {Co}_4\hbox {O}_9$ ${Ca}_{3 - x} {Bi}_{x} {Co}_{4} O_{9}$ (x = 0, 0.1, 0.3, 0.5) polycrystalline samples are synthesized by the solid-state method and compacted by SPS method. There is an increase in the intergranular energy barrier and a decrease in the thermopower S and figure of merit ZT of single-phase samples with an increase in x to 0.3. In all samples at T < 20 K, the spin glass (SG) state is observed. The effective magnetic moment $\mu _{eff}$ $μ_{eff}$ increases when Ca is replaced by Bi. The peak $\mu _{eff}$ $μ_{eff}$ is associated with the appearance of the SG state. The local disorder in the spin subsystem leading to an additional drop in $\sigma$ $σ$ described by variable-range hopping conductivity is associated with the appearance of the SG state. At T < 270 K, anomalies in $\chi$ $χ$ (T), $\mu _{eff}$ $μ_{eff}$ (T), and S(T) are found. These anomalies are associated with a spin transition (a change in the spin state of some $\hbox {Co}^{3+}$ ${Co}^{3 +}$ ions from S = 1 to 2).

Graphical abstract

Thermoelectric and magnetic properties of Bi-substituted \(\hbox {Ca}_3\hbox {Co}_4\hbox {O}_9\) polycrystalline samples

摘要