To be provided is a metal paste from which an electrode having high electrode activity as a sensor electrode of various gas sensors can be produced. The present invention is a metal paste for forming a gas sensor electrode obtained by dispersing a conductive particle including Pt or a Pt alloy and a ceramic powder including zirconia or stabilized zirconia, or any of zirconia and stabilized zirconia and one or more oxides of La, Ce, Pr, Nd, Sm, and Hf in a solvent, the metal paste further including an inorganic oxide particle containing alumina and an insoluble particle that is insoluble in the solvent, in which 0.5 or more to 3.0 mass % or less of the inorganic oxide particle and 1.0 to 5.0 mass % of the insoluble particle are dispersed based on the mass of the solid content of the conductive particle, the ceramic powder, the inorganic oxide particle, and the insoluble particle.

A membrane electrode assembly according to the present disclosure includes an electrolyte membrane containing a solid electrolyte and a first electrode bonded to the electrolyte membrane, wherein the solid electrolyte is a compound represented by the composition formula (1): BaZr.sub.1-xM.sub.xO.sub.3-γ, M in the composition formula (1) is at least one element selected from the group consisting of Sc, Er, Ho, Dy, Gd, Y, In, Tm, Yb, and Lu, and 0<x<1 and 0<γ<0.5 are satisfied, and the first electrode contains a lanthanum strontium cobalt iron palladium composite oxide.

An oriented apatite-type oxide ion conductor includes a composite oxide expressed as A.sub.9.33+x[T.sub.6.00−yM.sub.y]O.sub.26.0+z, where A represents one or two or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Be, Mg, Ca, Sr, and Ba, T represents an element including Si or Ge or both, and M represents one or two or more elements selected from the group consisting of B, Ge, Zn, Sn, W, and Mo, and where x is from −1.00 to 1.00, y is from 0.40 to less than 1.00, and z is from −3.00 to 2.00.

A high temperature carbon monoxide sensor for in-situ combustion monitoring is provided having a yttrium-stabilized zirconia interface based emf-measuring electrochemical sensor and a nickel oxide (NiO) first sensing electrode for targeting carbon monoxide gas at a temperature range from between about 1000 degrees Centigrade to about 1200 degrees Centigrade. A method of measuring carbon monoxide using this sensor is provided.

A gas sensor includes: a metal tubular body including a through hole allowing a sensor element to penetrate in an axial direction; and a powder compact being filled between an inner surface of the tubular body constituting the through hole and the sensor element, and sealing between both end portion sides of the sensor element. At least a range of a through hole inner surface to come into contact with the powder compact filled between the inner surface and the sensor element is a stripe-like recessed and projecting region in which projecting portions and recessed portions are alternately arranged in the axial direction and those portions extend along an inner circumferential direction of the tubular body. An interval between the projecting portions in the axial direction is 50 μm to 150 μm. The following expressions are satisfied, 0.3 μm≤Rz1≤10 μm, and Rz1/Rz2≥2.0.

A preparation method of indium oxide with stable morphology includes: (1) mixing indium oxide powder and bismuth oxide powder according to a mass ratio of 1:0.1-0.5 to obtain a powder mixture; (2) putting the powder mixture into a ball mill for ball milling at room temperature to obtain a uniform powder mixture; (3) putting the obtained uniform powder mixture into a muffle furnace and calcining at 700-1000° C.; and (4) obtaining the indium oxide with cubic stable morphology after the muffle furnace naturally cools to room temperature. The method has advantages of simple synthesis process, short synthesis period, high sample yield, no need of complicated equipment, and morphology of the obtained indium oxide can be maintained after being heated at a high temperature within 1000° C. for 2 hours. An electrochemical sensor prepared by using the indium oxide obtained by the method has better selectivity to nonane.

A control device performs deterioration diagnosis of a gas sensor including a pump cell and a sensor cell. The control device includes a control unit, a determination value acquisition unit, a diagnosis unit, and a correction unit. The control unit temporarily reduces the oxygen removal capability of the pump cell. The determination value acquisition unit acquires an output ratio of the sensor cell based on an output value of the sensor cell in a state where the oxygen removal capability of the pump cell is temporarily reduced. The diagnosis unit performs deterioration diagnosis of the gas sensor by comparing the output ratio with a determination threshold. The correction unit sets a correction coefficient based on an atmospheric pressure and an oxygen concentration, and also corrects the output ratio using the correction coefficient.

A gas sensor includes: a laminate formed of a plurality of layers including at least one layer of a solid electrolyte; a reference gas chamber formed in the laminate and containing a reference gas; and a reference electrode partially exposed in the reference gas chamber. A portion which is not exposed in the reference gas chamber, of the reference electrode is sandwiched between, among the layers, a first layer and a second layer adjacent to the first layer. When an area of the portion sandwiched between the first layer and the second layer, of the reference electrode is defined as a first area, and an area of a portion exposed in the reference gas chamber, of the reference electrode is defined as a second area, a ratio of the first area to the second area is 0.3 or more.

Provided is room temperature stable δ-phase Bi.sub.2O.sub.3. Ion conductive compositions comprise at least 95 wt % δ-phase Bi.sub.2O.sub.3, and, at 25° C., the compositions are stable and have a conductivity of at least 10.sup.−7 S/cm. Related methods, electrochemical cells, and devices are also disclosed.

There is provided a solid electrolyte including stabilized or partially stabilized zirconia, and a gas sensor provided with the solid electrolyte. A change rate of a crystallite diameter for at least one of a cubic phase and a tetragonal phase in crystal particles constituting the solid electrolyte, before and after heating the solid electrolyte from room temperature to 1200° C., is 10% or less. The solid electrolyte preferably includes partially stabilized zirconia.