Thermoelectric performance and crystal phase of calcium cobalt oxides sintered in oxygen gas

Abstract

Calcium hydroxide and tricobalt tetroxide were used as starting materials in a Ca:Co molar ratio of 3:4 and sintered at 1073-1373 K in a pure oxygen atmosphere.Polycrystalline single-phase Ca 3 Co 4 O 9 was obtained at all sintering temperatures in oxygen gas, and comparison with a sample sintered in air showed that controlling the oxygen partial pressure during sintering was important. In the sample sintered at 1373 K, the Seebeck coefficient was slightly lower than that of the samples sintered at lower temperatures, but the resistivity was decreased by half, so the power factor was doubled. K E Y W O R D S oxides, thermoelectric properties

Engineering Faceted Nanoporosity by Reactions in Thin-Film Oxide Multilayers in Crystallographically Layered Calcium Cobaltate for Thermoelectrics

“…In fact, the pore characteristics of seen for Ca 3 Co 4 O 9 formation, leading to faceted and oriented nanopores. This explanation is supported by the fact that bulk reactions of micropowdered forms of CaO and Co 3 O 4 yield microporous Ca 3 Co 4 O 9 , 51,52 with no traces of nanoscale porosity with faceting or texture. Therefore, we infer that for stacks of nanometer-scale-thick layers of the reactants, textured nanograins, crystallographic relationships, and density difference between the reactants and the product are key features that allow textured nanopores in Ca 3 Co 4 O 9 .…”

Фазово-Неоднородная Термоэлектрическая Керамика На Основе Слоистого Кобальтита Кальция, Полученная Двухстадийным Спеканием

“…Попытки снижения пористости керамики путем спекания ее при повышенных температурах [3,4] не приводят к значительному успеху, поскольку вследствие протекания реакций (1) (на воздухе при T > 1199 К [5], 1222 К [6]) и (2) (на воздухе при T > 1299 К [5], 1313 К [6]) (1) (2) образующаяся керамика является многофазной и низкопроводящей, что обусловливает низкие значения ее функциональных характеристик. Использование при синтезе керамики на основе Ca 3 Co 4 O 9 + δ вместо традиционного твердофазного различных растворных методов синтеза (цитратный, золь-гель и др.)…”