Abstract: By using a potassium ion secondary battery positive electrode active material comprising a potassium compound represented by general formula (1): KnMOm, wherein M is copper or iron, n is 0.5 to 3.5, and m is 1.5 to 2.5, provided is a potassium ion secondary battery positive electrode active material having higher theoretical discharge capacity and higher effective capacity than a potassium secondary battery using Prussian blue as a positive electrode active material.

Abstract: Provided is a material that can be used as a potassium secondary battery positive electrode active material (particularly a potassium ion secondary battery positive electrode active material), other than Prussian blue, by using a potassium compound and a potassium ion secondary battery positive electrode active material comprising the potassium compound, the potassium compound being represented by general formula (1): KnAkBOm, wherein A is a positive divalent element in groups 7 to 11 of the periodic table; B is positive tetravalent silicon, germanium, titanium or manganese, excluding a case in which A is manganese and B is titanium, and a case in which A is cobalt and B is silicon; n is 1.5 to 2.5; and m is 3.5 to 4.5.

Abstract: By using a potassium ion secondary battery positive electrode active material comprising a potassium compound represented by general formula (1): KnMm, wherein M is copper or iron, n is 0.5 to 3.5, and m is 1.5 to 2.5, provided is a potassium ion secondary battery positive electrode active material having higher theoretical discharge capacity and higher effective capacity than a potassium secondary battery using Prussian blue as a positive electrode active material.

Abstract: Provided is a material that can be used as a potassium secondary battery positive electrode active material (particularly a potassium ion secondary battery positive electrode active material), other than Prussian blue, by using a potassium compound and a potassium ion secondary battery positive electrode active material comprising the potassium compound, the potassium compound being represented by general formula (1): KnAkBOm, wherein A is a positive divalent element in groups 7 to 11 of the periodic table; B is positive tetravalent silicon, germanium, titanium or manganese, excluding a case in which A is manganese and B is titanium, and a case in which A is cobalt and B is silicon; n is 1.5 to 2.5; and m is 3.5 to 4.5.

Abstract: The present invention provides a complex oxide having a composition represented by the formula La1?xMxNiO2.7?3.3 or (La1?xMx)2NiO3.6?4.4 (wherein M is at least one element selected from the group consisting of Na, K, Li, Zn, Pb, Ba, Ca, Al, Nd, Bi and Y, and 0.01?×?0.8), the complex oxide having a negative Seebeck coefficient at 100° C. or higher. This complex oxide is a novel material which exhibits excellent properties as an n-type thermoelectric material.

Abstract: The present invention provides a complex oxide having a composition represented by the formula La1-xMxNiO2.7-3.3 or (La1-xMx)2NiO3.6-4.4 (wherein M is at least one element selected from the group consisting of Na, K, Li, Zn, Pb, Ba, Ca, Al, Nd, Bi and Y, and 0.01?x?0.8), the complex oxide having a negative Seebeck coefficient at 100° C. or higher. This complex oxide is a novel material which exhibits excellent properties as an n-type thermoelectric material.

Abstract: The present invention provides a method by which an oxide material having excellent thermoelectric conversion performance can be produced by a simple process. Specifically, the present invention provides a method for producing a composite oxide single crystal in which a mixture of raw substances including a Bi-containing substance, a Sr-containing substance, a Ca-containing substance, a Co-containing substance and a Te-containing substance, or a mixture of raw substances also including a Pb-containing substance in addition to the above-mentioned substances, is heated in an oxygen-containing atmosphere at a temperature below the melting point of any of the raw substances. The composite oxide single crystal produced by the method of the present invention is a ribbon-shaped fibrous single crystal that is about 10 to 10,000 ?m long, about 20 to 200 ?m wide, and about 1 to 5 ?m thick.