An oxide superconductor includes: REBa.sub.2Cu.sub.3O.sub.7-x (RE being one element selected from a “RE element group” of Pr, Nd, Sm, Eu, Gd, Y, Tb, Dy, Ho, Er, Tm, Yb, and Lu). The RE includes at least three types of metallic elements (M1, M2, and M3), and the three types of metallic elements are any element of the RE element group selected in order. In an oxide system satisfying R(M1)≤20 mol % and R(M2)≥60 mol % and R(M3)≤20 mol %, R(M1) being an average metallic element ratio of M1 in M1+M2+M3, SD(Ms)>0.15 is satisfied at a position at 50% of an average film thickness of a cross section including the c-axis, Ms being the metallic element of not larger of R(M1) and R(M3), SD(Ms) being a standard deviation/average value of a concentration of Ms.

An oxide superconducting wire includes a superconducting layer deposited on a substrate. The superconducting layer includes an oxide superconductor RE-Ba—Cu—O and artificial pinning centers ABO.sub.3, where RE is a rare earth element, A is Ba, Sr or Ca, and B is Hf, Zr, or Sn. In a TEM image of a cross-section of the superconducting layer, a standard deviation σ of an inclination angle of the artificial pinning center rods with respect to a cross-sectional direction of the superconducting layer is 6.13° to 11.73° and an average length of the artificial pinning center rods is 19.84 to 25.44 nm.

A superconducting composition of matter including overlapping first and second regions. The regions comprise unit cells of a solid, the first region comprises an electrical insulator or semiconductor, and the second region comprises a metallic electrical conductor. The second region extends through the solid and a subset of said second region comprise surface metal unit cells that are adjacent to at least one unit cell from the first region. The ratio of the number of said surface metal unit cells to the total number of unit cells in the second region being at least 20 percent.

An oxide superconducting wire includes a superconducting layer deposited on a substrate. The superconducting layer includes an oxide superconductor RE-Ba—Cu—O and artificial pinning centers ABO.sub.3, where RE is a rare earth element, A is Ba, Sr or Ca, and B is Hf, Zr, or Sn. In a TEM image of a cross-section of the superconducting layer, a standard deviation σ of an inclination angle of the artificial pinning center rods with respect to a cross-sectional direction of the superconducting layer is 6.13° to 11.73° and an average length of the artificial pinning center rods is 19.84 to 25.44 nm.

A method for producing a solid composition according to the present disclosure includes producing an oxide to be converted into a first functional ceramic by reacting with an oxoacid compound, and mixing the oxide, the oxoacid compound, and a second functional ceramic that is different from the first functional ceramic. The oxoacid compound preferably contains at least one of a nitrate ion and a sulfate ion as an oxoanion.

An oxide superconductor according to an embodiment includes an oxide superconducting layer includes a single crystal having a continuous perovskite structure containing at least one rare earth element selected from the group consisting of yttrium, lanthanum, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium, barium, and copper, containing praseodymium in a part of the site of the rare earth element in the perovskite structure, and having a molar ratio of praseodymium of 0.00000001 or more and 0.2 or less with respect to the sum of the at least one rare earth element and praseodymium; fluorine in an amount of 2.0×10.sup.15 atoms/cc or more and 5.0×10.sup.19 atoms/cc or less; and carbon in an amount of 1.0×10.sup.17 atoms/cc or more and 5.0×10.sup.20 atoms/cc or less.

A method for producing a solid composition according to the present disclosure is a method for producing a solid composition that is used for forming a functional ceramic having a first crystal phase. The method for producing a solid composition includes: producing an oxide composed of a second crystal phase different from the first crystal phase; and mixing the oxide and an oxo acid compound.

An oxide superconductor according to an embodiment includes an oxide superconducting layer includes a single crystal having a continuous perovskite structure containing at least one rare earth element selected from the group consisting of yttrium, lanthanum, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium, barium, and copper, containing praseodymium is a part of the site of the rare earth element in the perovskite structure, and having a molar ratio of praseodymium of 0.00000001 or more and 0.2 or less with respect to the sum of the at least one rare earth element and praseodymium; fluorine in an amount of 2.010.sup.15 atoms/cc or more and 5.010.sup.19 atoms/cc or less; and carbon in an amount of 1.010.sup.17 atoms/cc or more and 5.010.sup.20 atoms/cc or less.

An oxygen sensor element made of a ceramic sintered body detects oxygen concentration based on an electric current value measured when a voltage is applied. The ceramic sintered body has a composition formula LnBa.sub.2-xSr.sub.xCu.sub.3O.sub.7- generated by substituting any element selected from group 2 elements in the periodic table, such as strontium (Sr), for a part of a composition formula LnBa.sub.2Cu.sub.3O.sub.7- (Ln denotes rare earth element and is 0 to 1). Sr substitution quantity x should satisfy an inequality constraint 0<x1.5. This allows provision of an oxygen sensor element that improves durability etc. without losing sensor characteristics.

An oxide superconductor includes: REBa.sub.2Cu.sub.3O.sub.7-x (RE being one element selected from a RE element group of Pr, Nd, Sm, Eu, Gd, Y, Tb, Dy, Ho, Er, Tm, Yb, and Lu). The RE includes at least three types of metallic elements (M1, M2, and M3), and the three types of metallic elements are any element of the RE element group selected in order. In an oxide system satisfying R(M1)20 mol % and R(M2)60 mol % and R(M3)20 mol %, R(M1) being an average metallic element ratio of M1 in M1+M2+M3, SD(Ms)>0.15 is satisfied at a position at 50% of an average film thickness of a cross section including the c-axis, Ms being the metallic element of not larger of R(M1) and R(M3), SD(Ms) being a standard deviation/average value of a concentration of Ms.