Thermoelectric properties of (Na,M)xCoO2 (M= Li, K, Cs)ceramics

The (Na,M)xCoO2(M= Li, K, Cs, x= 0.55, 0.89) ceramics was synthesized, and its phase composition, thermal expansion, electrical conductivity and thermo-EMF were investigated. The materials obtained were polyphase ones and theyconsisted of sodium cobaltite (?-NaxCoO2), Co3O4and of other alkaline metals cobaltites (LiCoO2, KCoO2, Cs2CoO3). The temperature dependences of electrical conductivity of the (Na,M)0.55CoO2(M= K, Cs) and (Na,M)0.89CoO2samples had semiconducting character, but (Na,Li)0.55CoO2ones had metallic character. The materials studied were p-type conductors, which thermo-EMF and power factor (P) values rose at temperature increasing, and values of linear thermal expansion coefficient varied within (11.1–14.9) · 10 –6 K –1 . Inserting into Na0.55CoO2ceramics the lithium or potassium oxides increased its power factor, thus, for Na0.28K0.27CoO2compound P1100= 361 ?W ?m –1 ?K –2 , which was 85% higher than for Na0.55CoO2

Электрохимическое легирование кислороддефицитных оксидов YBa2Cu3O7-x и PrBaCuFeO5+x серой

Sulfur as a heteroadditive has been incorporated into oxygen-deficient YBa2Cu307-x and PrBaCuFeO5+x perovskites (ODP) using sulfur-ion-conducting solid electrolytes (CaPr2S4 and BaSm2S4). Composition of ODPs doped by sulfur was monitored by measuring electrical conductivity in combination with EMF method. The mechanism of sulfur incorporation into crystal lattice of nonstoichiometric layered YBa2Cu307-x and PrBaCuFeO5+x ODP has been proposed. Partial molar dissolution values of sulfur trace amounts in PrBaCuFeO5+x have been calculated.Проведено электрохимическое введение гетеропримеси - серы - в кислороддефицитные перовскиты (КДП) YBa2Cu3O7-x и PrBaCuFeO5+x с помощью сульфидионпроводящих твердых электролитов (CaPr2S4 и BaSm2S4). Контроль за составом легированных серой КДП осуществляли методом электропроводности в сочетании с методом ЭДС. Предложен механизм встраивания серы в кристаллическую решетку нестехиометрических слоистых КДП YBa2Cu3O7-x и PrBaCuFeO5+x. Рассчитаны парциальные молярные величины растворения микроколичеств серы в PrBaCuFeO5+

Thermoelectric properties of (Na,M)xCoO2 (M= Li, K, Cs)ceramics

The (Na,M)xCoO2(M= Li, K, Cs, x= 0.55, 0.89) ceramics was synthesized, and its phase composition, thermal expansion, electrical conductivity and thermo-EMF were investigated. The materials obtained were polyphase ones and theyconsisted of sodium cobaltite (?-NaxCoO2), Co3O4and of other alkaline metals cobaltites (LiCoO2, KCoO2, Cs2CoO3). The temperature dependences of electrical conductivity of the (Na,M)0.55CoO2(M= K, Cs) and (Na,M)0.89CoO2samples had semiconducting character, but (Na,Li)0.55CoO2ones had metallic character. The materials studied were p-type conductors, which thermo-EMF and power factor (P) values rose at temperature increasing, and values of linear thermal expansion coefficient varied within (11.1–14.9) · 10 –6 K –1 . Inserting into Na0.55CoO2ceramics the lithium or potassium oxides increased its power factor, thus, for Na0.28K0.27CoO2compound P1100= 361 ?W ?m –1 ?K –2 , which was 85% higher than for Na0.55CoO2