Fused product of scandia-stabilised zirconia

Abstract

The invention relates to an electrochemical device comprising and powder of a polycrystalline fused product of formula (Sc2O3)yAx(ZrO2 + HfO2)1-x-y, with 0.030 < y < 0.150, and 0.000 ≤ x ≤ 0.070, and x ≤ y, A denoting an additive selected from Y2O3, Al2O3, CeO2, Yb2O3, Gd2O3, MnO, Bi2O3, La2O3, Pr2O3, Nd2O5, Sm2O3, Eu2O3, Tb4O7, Ta2O5, Nb2O5 and mixtures thereof, ZrO2 + HfO2 + Sc2O3 + A representing more than 98% of the mass of the fused product, MnO expressing the total content of manganese oxides expressed in the form MnO, Pr2O3 expressing the total content of praseodymium oxides expressed in the form Pr2O3, Nd2O5 expressing the total content of neodymium oxides expressed in the form Nd2O5, Tb4O7 expressing the total content of terbium oxides expressed as Tb4O7, Ta2O5 expressing the total content of tantalum oxides expressed as Ta2O5, and Nb2O5 expressing the total content of niobium oxides expressed as Nb2O5.

Description

[0001]Description Title: Scandied Zirconia Fused Product Technical Field The present invention relates to a scandied zirconia fused product and a method for manufacturing such a product. The invention also relates to a device comprising a fused product according to the invention or a fused product manufactured or capable of being manufactured by a method according to the invention. Prior Art Scandied zirconia products are notably used as electrolytes in solid oxide electrochemical devices, particularly in solid oxide electrolysis cells (SOECs) or solid oxide fuel cells (SOFCs). For this purpose, a scandied zirconia powder having a median particle size typically less than or equal to 1 µm is conventionally sintered. Scandied zirconia products are also used for manufacturing anodes in electrochemical devices.The properties required for the electrolyte in these devices are not, however, identical to those required for an anode. Scandied zirconia powders are generally produced by solid-phase sintering, coprecipitation, or sol-gel processes. These processes are, however, complex and expensive to implement. Therefore, there is an ongoing need to reduce the complexity and cost of manufacturing a scandiated zirconia product suitable for use in the aforementioned applications. One object of the invention is to satisfy, at least partially, this need.Summary of the Invention According to a first principal aspect of the invention, this goal is achieved by means of a polycrystalline molten product of formula (Sc2O3)yAx(ZrO2 + HfO2)1-xy, with 0.030 ≤ y ≤ 0.150, and 0.000 ≤ x ≤ 0.070, and x ≤ y, where A denotes an additive selected from Y2O3, Al2O3, CeO2, Yb2O3, Gd2O3, MnO, Bi2O3, La2O3, Pr2O3, Nd2O5, Sm2O3, Eu2O3, Tb4O7, Ta2O5, Nb2O5 and mixtures thereof, ZrO2 + HfO2 + Sc2O3 + A representing more than 98% of the mass of said molten product, and MnO expressing the total content of manganese oxides expressed as MnO,Pr2O3 expressing the total content of praseodymium oxides expressed as Pr2O3, Nd2O5 expressing the total content of neodymium oxides expressed as Nd2O5, Tb4O7 expressing the total content of terbium oxides expressed as Tb4O7, Ta2O5 expressing the total content of tantalum oxides expressed as Ta2O5, Nb2O5 expressing the total content of niobium oxides expressed as Nb2O5.Such a product proved well-suited for use as an electrolyte in a solid oxide electrochemical device, particularly a solid oxide electrolysis cell or a solid oxide fuel cell. Unexpectedly, the inventors discovered that it was not necessary to implement a complex process to manufacture a product, especially a powder, suitable for making an electrolyte, as required by the prior art. A simple melting process is sufficient.Preferably, a molten product according to the invention further comprises one and preferably several of the following optional characteristics: - the additive is chosen from Al2O3, CeO2, Yb2O3 and mixtures thereof, preferably from Al2O3, CeO2 and mixtures thereof, preferably CeO2; - the product comprises, in mass percentages based on the crystallized phases of zirconia and hafnia, an amount of (monoclinic zirconia + monoclinic hafnia) less than or equal to 30%, preferably less than or equal to 10%; - the product is in the form of a particle having a sphericity greater than 0.8; - 0.130 ≥ y ≥ 0.040 and / or x ≤ 0.050; - 0.110 ≥ y ≥ 0.050 and / or x ≤ 0.030; - x ≤ 0.015; - y = 0.060 or y = 0.100; - x = 0.000 or x ≥ 0.005; - x = 0.01 and the additive is CeO2 or is Al2O3; - the product has an average zirconia crystallite size greater than or equal to 5 nm and less than or equal to 10 nm.The invention also relates to a powder comprising more than 90%, preferably more than 95%, preferably 100% by mass of particles in a molten product according to the invention. The powder preferably has a median size D. 50greater than 0.2 µm and less than 50 µm, preferably less than 1 µm. The invention also relates to a method for manufacturing a product according to the invention, said method comprising the following steps: a) mixing raw materials to form a starting charge; b) melting the starting charge until a molten material is obtained; c) cooling until the molten material has completely solidified, said starting charge being adapted, in step a), to obtain, at the end of step c) a molten product according to the invention; d) optionally, grinding said molten product, preferably until a powder is obtained; e) optionally, particle size selection of said molten product; f) before or after step d), optionally, annealing heat treatment of said molten product. In step a), the starting charge preferably contains scandi zirconia.The melt manufacturing process according to the invention thus advantageously provides a recycling solution for a scandiated zirconia product, in particular an electrolyte manufacturing waste product, before or after sintering. Such a product "to be recycled" may, in particular, be a product, melted or not, polycrystalline or not, containing, or even composed of, zirconia of the formula (Sc2O3). y HAS x (ZrO2 + HfO2) 1-x-y, x may be zero or not. The invention also relates to a molten product obtained or capable of being obtained by a process according to the invention. The invention further relates to an electrolyte comprising, or even being constituted by, a molten product according to the invention or obtained or capable of being manufactured by a process according to the invention, in particular obtained by sintering a particulate mixture comprising a powder according to the invention. Finally, the invention relates to a solid oxide electrochemical device, in particular a solid oxide electrolysis cell or a solid oxide fuel cell, comprising said electrolyte according to the invention. Moreover, the inventor has observed that the molten product according to the invention has a surprisingly small average zirconia crystallite size, particularly after grinding to obtain a powder, in particular a powder having a median size D50 greater than 0.1 µm, preferably greater than 0,2 µm and less than 50 µm, preferably less than 1 µm. According to a second principal aspect, the invention further relates to a product of the formula (Sc2O3)yAx(ZrO2 + HfO2)1-xy, with 0.030 ≤ y ≤ 0.150, and 0.000 ≤ x ≤ 0.070, and x ≤ y, where A designates an additive selected from Y2O3, Al2O3, CeO2, Yb2O3, Gd2O3, MnO, Bi2O3, La2O3, Pr2O3, Nd2O5, Sm2O3, Eu2O3, Tb4O7, Ta2O5, Nb2O5 and mixtures thereof, ZrO2 + HfO2 + Sc2O3 + A representing more than 98% of the mass of said product, and MnO expressing the total content of manganese oxides expressed as MnO, Pr2O3 expressing the total content of praseodymium oxides expressed as Pr2O3, Nd2O5 expressing the total content of neodymium oxides expressed as Nd2O5, Tb4O7 expressing the total content of terbium oxides expressed as Tb4O7, Ta2O5 expressing the total content of tantalum oxides expressed as Ta2O5, Nb2O5 expressing the total content of niobium oxides expressed as Nb2O5,said product having an average zirconia crystallite size greater than or equal to 4 nm, preferably greater than or equal to 5 nm and less than or equal to 10 nm. The product is preferably in powder form, in particular a powder having a median size D50 greater than 0.1 µm, preferably greater than 0.2 µm and less than 50 µm, preferably less than 1 µm. The product is preferably a polycrystalline molten product manufactured by a process according to the invention. Furthermore, the inventor observed that a fine powder obtained after grinding a molten product according to the first aspect of the invention contained a significant amount of (monoclinic zirconia + monoclinic hafnia), which degrades the ionic conductivity properties of an electrolyte made from said powder. In continuing his research,The inventor discovered that increasing the cooling rate in step c) significantly limits the amount of (monoclinic zirconia + monoclinic hafnia) produced. They also discovered that step f) had a similar effect. According to a third principal aspect, the invention further relates to a method for manufacturing such a powder according to the invention, comprising the following steps: a) mixing raw materials to form a starting charge; b) melting the starting charge until a molten material is obtained; c) cooling the molten material until it has completely solidified to obtain a molten product; d) grinding the molten product; e) optionally, particle size selection of the powder; the grinding in step d) and the optional particle size selection in step e) being adapted to obtain a powder with a median size of less than 1 µm, preferably less than 0.7 µm.and preferably greater than 0.1 µm; (f) before or after step (d), optionally, annealing heat treatment of said molten product or powder, the starting charge in step (a) being adapted to obtain a powder in a polycrystalline molten product of formula (Sc2O3)yAx(ZrO2 + HfO2)1-xy, with 0.030 ≤ y ≤ 0.150, and 0.000 ≤ x ≤ 0.070, and x ≤ y, where A denotes an additive selected from Y2O3, Al2O3, CeO2, Yb2O3, Gd2O3, MnO, Bi2O3, La2O3, Pr2O3, Nd2O5, Sm2O3, Eu2O3, Tb4O7, Ta2O5, Nb2O5 and mixtures thereof, ZrO2 + HfO2 + Sc2O3 + A representing more of 98% of the mass of said product, MnO expressing the total content of manganese oxides expressed as MnO, Pr2O3 expressing the total content of praseodymium oxides expressed as Pr2O3, Nd2O5 expressing the total content of neodymium oxides expressed as Nd2O5, Tb4O7 expressing the total content of terbium oxides expressed as Tb4O7,Ta₂O₅ expressing the total content of tantalum oxides expressed as Ta₂O₅, Nb₂O₅ expressing the total content of niobium oxides expressed as Nb₂O₅. The invention also relates to said powder. In a first particular embodiment, said process is remarkable in that, at step c), the cooling rate of the molten material is greater than 15°C / s. Surprisingly, such a powder exhibits, as a mass percentage based on the crystallized phases of zirconia and hafnia, an amount of (monoclinic zirconia + monoclinic hafnia) less than or equal to 10%. Preferably, the cooling rate is greater than 50°C / s, preferably greater than 100°C / s. Pouring molten material into a mold as defined in US 3,993,119, or using a process for atomizing molten material, particularly steps c1) and c2) described later,are particularly well suited to achieving this cooling rate. The powder may advantageously have, as a mass percentage based on the crystallized phases of zirconia and hafnia, an amount of (monoclinic zirconia + monoclinic hafnia) less than or equal to 5%. In a second particular embodiment, which can be combined with the first, the process is notable in that it includes a step f). The powder obtained by this process may advantageously have, as a mass percentage based on the crystallized phases of zirconia and hafnia, an amount of (monoclinic zirconia + monoclinic hafnia) less than or equal to 10%, or less than or equal to 5%. This reduction in the amount of (monoclinic zirconia + monoclinic hafnia) is advantageously possible with cooling carried out at a rate greater than 15 °C / s, but also at a rate less than or equal to 15 °C / s.for example, at a cooling rate of less than 10°C / s, less than 5°C / s, less than 3°C / s, or less than 2°C / s, or less than 1°C / s. In one embodiment, at step f), the heat treatment temperature is greater than or equal to 800°C. Preferably, the temperature of said heat treatment is greater than or equal to 900°C, preferably greater than or equal to 1000°C and / or less than or equal to 1800°C, less than or equal to 1700°C, preferably less than or equal to 1600°C, preferably less than or equal to 1400°C, preferably less than or equal to 1200°C. Preferably, step f) takes place after step d). The invention also relates to the powder,in particular manufactured according to the process according to the first or second principal embodiments of the third principal aspect of the invention. This powder is remarkable in that it simultaneously exhibits a small median size and a low quantity of (monoclinic zirconia + monoclinic hafnia). According to a fourth principal aspect, the invention further relates to a polycrystalline molten product of formula (Sc2O3), y HAS x (ZrO2 + HfO2) 1-x-y , with 0.030 ≤ y ≤ 0.150, and 0.000 < x ≤ 0.070, preferably x ≥ 0.001, preferably x ≥ 0.005, preferably x ≥ 0.007; and x ≤ y, where A denotes an additive chosen from Y2O3, Al2O3, CeO2, Yb2O 3,Gd2O3, MnO, Bi2O3, La2O3, Pr2O3, Nd2O5, Sm2O3, Eu2O3, Tb4O7, Ta2O5, Nb2O5 and mixtures thereof, preferably selected from CeO2 and Al2O3, ZrO2 + HfO2 + Sc2O3 + A representing more than 98% of the mass of said product, MnO expressing the total content of manganese oxides expressed as MnO, Pr2O3 expressing the total content of praseodymium oxides expressed as Pr2O3, Nd2O5 expressing the total content of neodymium oxides expressed as Nd2O5, Tb4O7 expressing the total content of terbium oxides expressed as Tb4O7, Ta2O5 expressing the total content of tantalum oxides expressed as Ta2O5, Nb2O5 expresses the total content of niobium oxides expressed as Nb2O5. Remarkably, the presence of the additive, i.e., x > 0.000, is not detrimental to the properties of the product, particularly when the product is used as an electrolyte, or within an electrolyte, in an electrochemical device. It is even advantageous.It is thus possible to recycle scandiated zirconia products containing such an additive, and in particular polycrystalline fused products according to the invention, but also scandiated zirconia products containing such an additive and manufactured according to a prior art process, for example by solid-phase sintering, coprecipitation, or sol-gel. The invention therefore relates to a recycling process for a product to be recycled, preferably fused, preferably polycrystalline, comprising, or even made up of, a material of the formula (Sc2O3). y HAS x (ZrO2 + HfO2) 1-x-ywhere x can be zero or positive, the recycling process comprises steps a), b), and c), and optionally one or more of steps d), e), and f), of a manufacturing process according to the invention, the starting feed at step a) containing said product to be recycled, preferably in powder form. Said product to be recycled preferably comprises, in mass percentages based on the crystallized phases of zirconia and hafnia, an amount of (monoclinic zirconia + monoclinic hafnia) less than or equal to 30%. In a particularly advantageous embodiment, the product to be recycled is an electrolyte, in particular an electrolyte manufacturing waste product, before or after sintering, preferably an electrolyte from a solid oxide electrochemical device, in particular a solid oxide electrolysis cell or a solid oxide fuel cell.Preferably, the product obtained by the recycling process, i.e., the recycled product, is used in an electrolyte, preferably an electrolyte of a solid oxide electrochemical device, in particular a solid oxide electrolysis cell or a solid oxide fuel cell. Unless technically incompatible, the features of the various principal aspects of the invention can be combined. In particular, all the optional features of a molten product according to the first principal aspect of the invention are optionally applicable to the product according to the second principal aspect of the invention, to the powder according to the third principal aspect of the invention, and to the molten product according to the fourth principal aspect of the invention. Definitions: A "molten product" is a product directly obtained by solidifying a molten material resulting from the melting of a starting charge.By "directly obtained," we mean that the molten product is obtained immediately after solidification. A "molten material" is a mass made liquid by heating a starting charge, which may contain some solid particles, but not enough to structure the mass. To maintain its shape, a molten material must be contained within a vessel. A "polycrystalline" material is a solid material composed of numerous crystallites of varying sizes and orientations, as opposed to a monocrystalline material consisting of a single crystal. The polycrystalline nature of a material can be demonstrated, for example, by X-ray diffraction and / or by scanning electron microscopy. Such observations reveal grain boundaries. Without special precautions, a molten product is polycrystalline.A "particle" is defined as a solid object with all dimensions less than 10 mm. The sphericity of a particle is the ratio of its smallest dimension to its largest dimension. A "block" is defined as a solid object that is not a particle. A "powder" is a collection of particles. The 10th (D10), 50th (D50), 90th (D90), and 99.5th (D99.5) percentiles represent the particle sizes corresponding to the percentages, by mass, of 10%, 50%, 90%, and 99.5%, respectively, on the cumulative particle size distribution curve of the powder, with the particle sizes listed in ascending order. For example, 10% by mass of the powder particles are smaller than D10, and 90% by mass are particles larger than or equal to D10.Percentiles can be determined using a particle size distribution obtained with a laser particle size analyzer, for example, a Partica LA-950V2 marketed by HORIBA. The 10th percentile (D) is called the "minimum size of a powder". 10) of said powder. The "median size of a powder" is defined as the 50th percentile (D50) of said powder. The "maximum size of a powder" is defined as the 99.5th percentile (D99.5) of said powder. A "precursor" of a compound or element is understood to be a constituent capable of providing said compound or element, respectively, during the implementation of a manufacturing process according to the invention. A total content of several oxides, for example ZrO2 + HfO2, does not imply that each of said oxides is present, even if, in an embodiment, each of said oxides is present. When reference is made to ZrO2, it should be understood to mean (ZrO2 + HfO2), with HfO2 < 5%, preferably HfO2 < 3%. Indeed, a small amount of HfO2, chemically inseparable from ZrO2 and exhibiting similar properties, is always naturally present in zirconia sources. Hafnium oxide is therefore not considered an impurity.Similarly, when reference is made to the element zirconium, this should be understood to include the element Zr and traces of the element Hf present in the source of the element Zr. "Impurities" means constituents introduced unintentionally. Impurities are not necessary constituents, but merely tolerated. Unless otherwise specified, percentages used to define a composition are mass percentages based on the mass of the product. The verbs "include," "contain," and "present" should be interpreted in a non-restrictive manner unless otherwise specified. Detailed Description: Other features and advantages of the present invention will become apparent from the following detailed description, which is provided for illustrative purposes only and is not intended to be limiting.Molten product A molten product according to the invention preferably has one or more of the following optional characteristics: - the additive is chosen from Y2O3, Al2O3, CeO2, Yb2O. 3, Gd2O3, MnO, Bi2O3, La2O3, Pr2O3, Nd2O5, Sm2O3, Eu2O3, Tb4O7 and mixtures thereof, preferably from Al2O3, CeO2, Yb2O3 and mixtures thereof, preferably from Al2O3, CeO2 and mixtures thereof. Preferably the additive is CeO2. - in one embodiment, the content of "other constituents", i.e., constituents other than ZrO2, HfO2, Sc 2 O 3 , Y 2 O 3 , Al 2 O 3 , CeO 2 , Yb 2 O 3 , Gd 2 O 3. Manganese oxides, Bi2 O 3 , La 2 O3, praseodymium oxides, Nd2O5, Sm2O3, Eu2O3, terbium oxides, tantalum oxides and niobium oxides is less than 1.5%, preferably less than 1%, preferably less than 0.5%, preferably less than 0.3%; - y ≥ 0.040, preferably y ≥ 0.050, and / or y ≤ 0.130, preferably y ≤ 0.110; - in one embodiment, x = 0.000; - in one embodiment, x ≤ 0.070, preferably x ≤ 0.050, preferably x ≤ 0.040, preferably x ≤ 0.030, preferably x ≤ 0.020, preferably x ≤ 0.015 and x ≥ 0.001, preferably x ≥ 0.005, preferably x ≥ 0.007; - in one embodiment, y ≥ 0.040, preferably y ≥ 0.050, and y ≤ 0.130, preferably y ≤ 0.110, and x ≤ 0.050, preferably x ≤ 0.040, preferably x ≤ 0.030, preferably x ≤ 0.020, preferably x ≤ 0.015 and x ≥ 0.005, preferably x ≥ 0.007; - in another embodiment, y ≥ 0.040, preferably y ≥ 0.050, and y ≤ 0.130, preferably y ≤ 0.110, and x ≤ 0.050, preferably x ≤ 0.040,preferably x ≤ 0.030, preferably x ≤ 0.020, preferably x ≤ 0.015 and x ≥ 0.001, preferably x ≥ 0.005, preferably x ≥ 0.007, and the additive is chosen from Al2O3, CeO2, Yb2O3 and mixtures thereof, preferably from Al2O3, CeO2 and mixtures thereof; - In one embodiment, y = 0.060 or y = 0.100; - In one embodiment, y = 0.060 and x = 0.000; - In one embodiment, y = 0.060 and x ≥ 0.005; - In one embodiment, y = 0.060, x = 0.010 and the additive is CeO2; - In one embodiment, y = 0.060, x = 0.010 and the additive is Al2O3; - In another embodiment, y = 0.100 and x = 0.000; - In another embodiment, y = 0.100 and x ≥ 0.005; - In another embodiment, y = 0.100, x = 0.010 and the additive is CeO2; - In another embodiment, y = 0.100, x = 0.010 and the additive is Al2O3; - the molten product comprises, in mass percentages based on the crystallized phases of zirconia and hafnia,an amount of (monoclinic zirconia + monoclinic hafnia) less than or equal to 30%, preferably less than or equal to 25%, preferably less than or equal to 20%, preferably less than or equal to 15%, preferably less than or equal to 10%; - the average size of zirconia crystallites is preferably greater than or equal to 5 nm, preferably greater than or equal to 6 nm, preferably greater than or equal to 7 nm, and preferably less than or equal to 100 nm, preferably less than or equal to 80 nm, preferably less than or equal to 60 nm, preferably less than or equal to 50 nm, preferably less than or equal to 30 nm; - in one embodiment, particularly when the molten product has not undergone an annealing heat treatment step (f), the average size of the zirconia crystallites is greater than or equal to 5 nm, preferably greater than or equal to 6 nm, preferably greater than or equal to 7 nm,and less than or equal to 10 nm. In one embodiment, the molten product is in the form of an object, preferably a particle, having a sphericity greater than 0.5, preferably greater than 0.6, preferably greater than 0.7, or even greater than 0.8. The invention also relates to a powder comprising more than 90% by mass, or even more than 95%, or even substantially 100% of particles in a molten product according to the invention. The powder preferably has a median particle size D50 greater than 0.1 µm, preferably greater than 0.2 µm, preferably greater than 0.3 µm and / or, preferably, less than 50 µm, preferably less than 30 µm, preferably less than 10 µm, preferably less than 5 µm, preferably less than 3 µm, preferably less than 1 µm, preferably less than 0.7 µm. Preferably, the minimum particle size of the powder according to the invention is greater than 0.05 µm, preferably greater than 0.07 µm. Preferably,The maximum size of the powder according to the invention is less than 2 µm, preferably less than 1.5 µm. Preferably, the D90 percentile of the powder according to the invention is less than 1.5 µm, preferably less than 1.0 µm. In one embodiment, a powder according to the invention is sintered, optionally with at least one other powder, said at least one other powder preferably being a metal oxide powder, to form an electrolyte for a solid oxide electrochemical device, in particular a solid oxide electrolysis cell or a solid oxide fuel cell. The invention also relates to a method for manufacturing a molten product comprising steps a) to c) and optionally d) to f). In one embodiment, the method according to the invention comprises step d) and step e). In another embodiment, the method according to the invention comprises step d).a step e) and a step f). Step f) can in particular be implemented to reduce the amount of crystallized phase of (monoclinic zirconia + monoclinic hafnium) in the molten product according to the invention. In step a), a starting charge for manufacturing a molten product according to the invention is formed from compounds of zirconium, hafnium, scandium, and optionally from compounds of cerium, aluminum, yttrium, ytterbium, gadolinium, manganese, bismuth, europium, lanthanum, praseodymium, neodymium, samarium, terbium, tantalum and niobium, in particular in the form of oxides and / or carbonates and / or hydroxides and / or oxalates and / or nitrates. Preferably, at least one, or even all, of the elements zirconium, hafnium, scandium, and optionally the elements cerium, aluminium, yttrium, ytterbium, gadolinium, manganese, bismuth, europium, lanthanum, praseodymium, neodymium, samarium, terbium, tantalum and niobium,are introduced into the starting charge in the form of oxides. Preferably, zirconium, hafnium, scandium compounds, and optionally cerium, aluminium, yttrium, ytterbium, gadolinium, manganese, bismuth, europium, lanthanum, praseodymium, neodymium, samarium, terbium, tantalum and niobium compounds, are chosen from ZrO2, Sc2O3, carbonates and / or hydroxides and / or oxides of the elements cerium, aluminium, yttrium, ytterbium, gadolinium, manganese, bismuth, europium, lanthanum, praseodymium, neodymium, samarium, terbium, tantalum and niobium, respectively. In one embodiment, at least one of said compounds is chosen to provide at least two elements selected from zirconium, hafnium, scandium, cerium, aluminum, yttrium, ytterbium, gadolinium, manganese, bismuth, europium, lanthanum, praseodymium, neodymium, samarium, terbium, tantalum, and niobium. For example,Such a compound may be ceriated zirconia. In one embodiment the starting charge contains scandiated zirconia, preferably in the form of a powder. In this embodiment, the scandium zirconia present in the starting charge may also contain at least one oxide selected from the oxides of aluminum, yttrium, ytterbium, gadolinium, manganese, bismuth, europium, lanthanum, praseodymium, neodymium, samarium, terbium, tantalum, and niobium, particularly when the molten product obtained at the end of step c) contains said at least one oxide selected from the oxides of aluminum, yttrium, ytterbium, gadolinium, manganese, bismuth, europium, lanthanum, praseodymium, neodymium, samarium, terbium, tantalum, and niobium. This embodiment advantageously allows the use of scrap or offcuts of scandium zirconia. Preferably, compounds containing the elements zirconium, hafnium,Scandium and optionally cerium, aluminum, yttrium, ytterbium, gadolinium, manganese, bismuth, europium, lanthanum, praseodymium, neodymium, samarium, terbium, tantalum, and niobium together constitute more than 90%, preferably more than 99%, by mass percentage, of the constituents of the starting feed. Preferably, these compounds, together with the impurities, constitute 100% of the constituents of the starting feed. Preferably, no compounds other than those providing zirconium, hafnium, scandium, and optionally cerium, aluminum, yttrium, ytterbium, gadolinium, manganese, bismuth, europium, lanthanum, praseodymium, neodymium, samarium, terbium, tantalum, and niobium are intentionally introduced into the starting feed. Select the raw materials for the starting feed such that the molten product obtained at the end of step c),Achieving a composition that conforms to the desired one presents no difficulty for a person skilled in the art. They know how to adapt the composition of the starting charge, particularly according to the evaporation of certain raw materials during melting and the melting conditions used. These evaporations are small, and the quantities of zirconium, hafnium, scandium, and optionally cerium, aluminum, yttrium, ytterbium, gadolinium, manganese, bismuth, europium, lanthanum, praseodymium, neodymium, samarium, and terbium are small.Tantalum and niobium from the initial feedstock are substantially recovered in the resulting polycrystalline molten product. The initial feedstock is preferably in the form of a particulate mixture. The particle sizes of the powders used can be those commonly encountered in melting processes. The raw materials can be thoroughly mixed in a mixer. This mixture is then poured into a melting furnace. In step b), the initial feedstock is melted. All known furnaces are suitable, such as an induction furnace, a plasma furnace, or a Héroult-type electric arc furnace, provided they can melt the initial feedstock. Melting in a plasma torch or in a crucible within a heat treatment furnace, preferably an electric furnace, is also possible. Electrofusion advantageously allows the production of large quantities of molten product with attractive yields. Preferably,The starting charge is melted in a Héroult-type electric arc furnace. For example, a Héroult-type electric arc furnace with two electrodes and a chamber diameter of approximately 0.8 m, capable of holding approximately 180 kg of molten material, can be used. Preferably, when a Héroult furnace is used, the electrodes are not immersed in the molten material. In step b), the energy supplied is preferably greater than 1150 kWh / T of starting charge, and preferably greater than 1300 kWh / T. Preferably, the energy supplied is between 1150 kWh / T and 2800 kWh / T. The electrical voltage is, for example, 160 volts. After melting, the starting charge is in the form of molten material, which may contain some solid particles, but not enough to structure the molten material. By definition, to maintain its shape,A molten material must be contained in a vessel. The quality of the mixing of the molten material can be improved by bubbling a gas, as mentioned in FR 1208577. This bubbling gas can be air or oxygen. The general environment of the molten material is preferably oxidizing, preferably air. Preferably, step b) is carried out at atmospheric pressure. In step c), the cooling rate is preferably greater than 15°C / s and / or less than 3000°C / s, or even less than 1000°C / s. In a first embodiment of step c), step c) comprises the following steps: c1) dispersion of the molten material in the form of liquid droplets, c2) solidification of these liquid droplets by contact with a fluid, preferably a gas, so as to obtain particles of molten product. The molten product according to the invention, in particular manufactured according to this first embodiment, may be presented,at the end of step c), in the form of a powder of particles with a minimum size greater than 0.005 mm and a maximum size less than 5 mm. In step c1), a stream of the molten liquid is dispersed into liquid droplets. The dispersion may result from blowing the molten material through the stream. The molten particles may be spherical or not, hollow or solid, depending in particular on the blowing conditions and / or the composition of the molten material. Any other method of atomizing a molten material known to those skilled in the art is permissible. In step c1), the stream of said molten material is brought into contact with a "dispersion" fluid, preferably a "dispersion" gas. Preferably, the dispersion fluid is a gas having an oxygen content by volume greater than 20%, preferably air and / or water vapor, preferably air. In step c2),The liquid droplets are transformed into solid particles by contact with a "solidification" fluid, preferably a solidification gas, which can be selected from those described for step c1). Preferably, the process is adapted so that, as soon as it is formed, the molten liquid droplet is in contact with the solidification fluid, which may be the same as or different from the dispersion fluid used for step c1) and which, preferably, is the same as the dispersion fluid used for step c1). In one embodiment, step c2) includes cooling the droplets by immersion in water. Preferably, steps c1) and c2) include cooling the droplets by blowing a gas having an oxygen content by volume greater than 20%, preferably air, at ambient temperature. Preferably,No other means of solidification than cooling by contact with the solidification fluid is used. Preferably, the dispersion (step c1)) and solidification (step c2)) are substantially simultaneous, the molten material being dispersed by a fluid, preferably a gas, suitable for cooling and solidifying this material. Preferably, contact with the fluid is maintained at least until the droplets have completely solidified. At the end of step c2), a set of solid particles is obtained having a minimum size greater than or equal to 0.01 µm and a maximum size less than or equal to 5 mm, or even less than or equal to 3 mm, depending on the dispersion conditions. In a second embodiment,Step c) comprises the following steps: c1') pouring the molten material into a mold; c2') solidification by cooling the molten material poured into the mold until a block, at least partially solidified, is obtained; c3') demolding the block. In step c1'), the molten material is poured into a mold capable of withstanding the molten bath. Preferably, molds made of graphite, cast iron, or as defined in US 3,993,119 are used. In the case of an induction furnace, the coil is considered to constitute a mold. Preferably, the pouring is carried out under a "pouring" gas having an oxygen content by volume greater than 20%, preferably under air. In step c2'), the molten material poured into the mold is cooled until a block, at least partially solidified, is obtained. In step c3'), the block is demolded. Preferably,The block is demolded as soon as it has sufficient rigidity to substantially retain its shape. Preferably, in step c2') and / or after step c3'), the molten material being solidified is brought into contact, directly or indirectly, with a "solidification" fluid, preferably a "solidification" gas, which may be the same as or different from that described for step c1'). This contact can be made immediately after pouring. To facilitate contact between the molten material and the solidification fluid, preferably the solidification gas, it is preferable to demold the block as quickly as possible, if possible before complete solidification, and then immediately begin contacting it with the solidification fluid, preferably the solidification gas. Solidification then continues in step c3'). Preferably, contact with the solidification fluid is maintained,preferably the solidification gas, until the block is completely solidified. After complete solidification, a block is obtained that, after steps d) and optionally e) and f), yields a powder of particles of the molten product according to the invention. In optional step d), the resulting molten product is crushed and / or ground to reduce the size of the pieces, preferably to a powder of molten particles having a median size D50 preferably greater than 0.1 µm, preferably greater than 0.2 µm, preferably greater than 0.5 µm and / or, preferably, less than 50 µm, preferably less than 30 µm, preferably less than 10 µm, preferably less than 5 µm, preferably less than 3 µm, preferably less than 1 µm, preferably less than 0.7 µm. All types of crushers and grinders are suitable for reducing the size of the pieces, with grinding preferably carried out dry and / or in a solvent.Preferably water. An attrition mill, an air jet mill, or a ball mill are well suited. In one embodiment, the product obtained after crushing is de-ironed using any technique known to those skilled in the art. The molten particle powder may also undergo, particularly after step d), a further step to form agglomerates or aggregates. All techniques known to those skilled in the art may be used, in particular, slurry atomization or granulation. In the optional step e), particle size selection is then carried out, depending on the intended application, for example, by sieving or cycloning. In one embodiment, the process according to the invention comprises steps d) and e). In the optional step f), the molten product is then subjected to a heat treatment by annealing. Advantageously,Step f) makes it possible, in particular, to reduce the amount of crystallized phase of (monoclinic zirconia + monoclinic hafnia) in the molten product according to the invention. The molten product, preferably in the form of particles, is introduced into a furnace for annealing. The annealing temperature is lower than the melting temperature of the molten product and preferably above 800°C, preferably above 900°C, and preferably below 1400°C, preferably below 1300°C, preferably below 1200°C, preferably below 1150°C, preferably below 1100°C. The holding time at the annealing temperature is preferably greater than 2 hours and / or preferably less than 24 hours. Preferably, the molten product is annealed under an atmosphere containing a gas with an oxygen content greater than 20% by volume, preferably air. When the process includes step f),The molten product according to the invention can be ground and / or undergo a particle size selection step, before and / or after said step f). In one embodiment, the process according to the invention comprises steps d) and f). Preferably, in said embodiment, step f) is performed, then step d). In one embodiment, the process according to the invention comprises steps d), e), and f), said steps being able to be performed in any order, step f) being, for example, before step d). Preferably, in said embodiment, a step f) is performed, then a step d), then a step e). Examples The following non-limiting examples are given for the purpose of illustrating the invention. Measurement protocols The following measurement protocols were used to determine certain properties of the molten products. For each example, the chemical analysis, carried out after drying at 80°C for 12 hours,is measured by inductively coupled plasma spectrometry (ICP) for elements present at concentrations not exceeding 0.5%. To determine the content of other elements, the sample is dried at 80°C for 12 hours, then a bead of the sample is produced by melting, and chemical analysis is performed by X-ray fluorescence. Any carbon and sulfur content is measured using a CS744 carbon-sulfur analyzer, marketed by LECO. The median particle size of a powder is measured conventionally using a Partica LA-950V2 laser particle size analyzer, marketed by Horiba. For each example, the quantity of (monoclinic zirconia + monoclinic hafnia), expressed as mass percentages based on the total mass of the crystallized zirconia and hafnia phases in the sample powder, is determined by X-ray diffraction.After the powder was deagglomerated using an agate mortar, the diffraction pattern was acquired using a Bruker D8 Endeavor instrument, over an angular range 2θ between 5° and 100°, with a step size of 0.01° and a counting time of 0.34 s / step. The front optics consisted of a 0.3° primary slit and a 2.5° Soller slit. The sample was rotated at a speed of 5 rpm using the automatic cutter. The rear optics consisted of a 2.5° Soller slit, a 0.0125 mm nickel filter, and a 1D detector with a 4° aperture. The diffraction patterns are then qualitatively analyzed using EVA software and the PDF-5+ 2024 database. Once the phases present are identified, the diffraction patterns are analyzed with HighScore Plus software from Malvern Panalytical.using Rietveld refinement with the following strategy: - define the background noise so that it is indistinguishable from the signal in areas without diffraction peaks, - select the previously determined background noise using "use available background", - import the PDF sheets of the identified phases and select "Spherical Harmonics" for each phase in the preferred orientations, - select the "Automatic (Default Rietveld)" mode and start the refinement, - switch to manual mode, and for each phase whose quantity is greater than 1% by mass and simultaneously: - in "spherical harmonics", select all the coefficients, and restart the refinement, then - select "U", and restart the refinement, then - select "V", and restart the refinement, then - select "Peak Shape 1", and restart the refinement, then - select "Peak Shape 2", and restart the refinement, then - select "Peak Shape 3",and restart the refinement, then -select "B Overall" of all phases simultaneously, and restart the refinement, then-select "Atomic coordinates", "Occupancy" on all atoms of the phases, and restart the refinement. The average size of the zirconia crystallites, D, of the powders in the examples is classically determined by X-ray diffraction on said powders using a Bruker D8 Endeavor type instrument, with the following Debye-Scherrer equation: Kλ 1 180 ^, = ^(^^ − ^^ xx) cos ^10^ - K being equal to 0.89, - λ being the wavelength of the X-rays, here equal to that of copper, i.e., 1.5418 Angstroms, - B being the full width at half maximum (FWHM) of the zirconia peak present at 2θ = 50°, in degrees - b being the FWHM of the peak located at 2θ = 35° of a LaB6 standard, reference NIST 660a, analyzed under the same conditions as the sample, and - 2θ being the angle of maximum intensity of the zirconia peak present at 2θ = 50°, in degrees. The acquisition of the diffraction patterns of the LaB6 standard and of each example is carried out under the same conditions as for the measurement of the quantity of (monoclinic zirconia + monoclinic hafnia). The full width at half maximum (FWHM) of the zirconia peak at 2θ = 50° in the example sample is determined as follows. On the diffraction pattern, a region containing the peak located at 2θ = 50° is selected.taking care that the area also includes a portion of the baseline and that the area does not contain any other peaks. After removing the Kα2 line, the width of the zirconia peak at 2θ = 50° is conventionally determined using the Highscore+ software from Malvern Panalytical, by inserting a peak at 2θ = 50° using the "Insert peak" function, and then performing automatic refinement using the "Default Profile Fit" function with a pseudo-Voigt function and a "split width" asymmetry. The full width at half maximum (FWHM) of the peak on the diffraction pattern at 2θ = 50°, B, is the value of the parameter ("total FWHM"). For the LaB6 standard, the FWHM of the peak located at 2θ = 35°, b, is determined using the same procedure. The average size of zirconia crystallites is then calculated using the Debye-Scherrer equation described previously. For examples,The PDF datasheets used for measuring the quantity of (monoclinic zirconia + monoclinic hafnia) and for measuring the average size of zirconia crystallites are datasheets 04-014-8566 and 04-014-8565. Manufacturing Protocol The molten product of Example 1 was prepared from the following raw materials: - zirconia powder with a purity greater than 99.9% by mass, and a median size of 15 µm; - scandium oxide powder with a purity greater than 99.9% by mass, and a median size of less than 40 µm. The molten product of Example 1 was prepared according to a manufacturing process according to the invention: a) mixing the raw materials to form a starting charge; b) melting of said starting charge in a single-phase Héroult-type electric arc furnace with engraphite electrodes, with a furnace chamber of 0.8 m in diameter, a voltage of 160 V,an intensity of 1500 A and a specific electrical energy supplied of 2500 kWh / T loaded; c1') pouring the molten material into a graphite mold; c2') solidification by cooling of the molten material poured into the mold until a block is obtained that is at least partially solidified; c3') demolding of the block; d) crushing of the block obtained at the end of step c), then grinding in a jar using zirconia balls with 3% mass of MgO, followed by attrition grinding in a LabStar mill marketed by the Netzsch company, for 7 hours of an aqueous suspension consisting of 4000 grams of the powder obtained after grinding in the jar, 1600 grams of Zirmil® Y beads with a median size of 1.25 mm, marketed by Saint-Gobain ZIRPRO and 5000 grams of demineralized water. After grinding by attrition,The resulting suspension is dried in an oven at 80°C for 12 hours to obtain a powder. This powder is then deagglomerated using an agate mortar. At step c2'), the cooling rate of the molten material is less than 1°C / s. Table 1 below provides the mass composition of the starting charge. [Table 1] Raw materials % mass Zirconia powder 93.3 Scandium oxide powder 6.7 Table 2 below provides the characterizations obtained on the molten particle powder, MnO, Pr2O3, Nd2O5, Tb4O7, Ta2O5 and Nb2O5, expressing the total contents of manganese, praseodymium, neodymium, terbium, tantalum and niobium oxides, respectively. [Table 2] Example 1 Chemical analysis, in mass percentages based on the mass of the product (ZrO2+HfO2) + Sc2O3+ Y2O3+ Al2O3+ CeO2+ Yb2O3+ Gd2O3+ MnO + Bi2O3+ complement to La2O3 + Pr2O3 + Nd2O5 + Sm2O3 + Eu2O3 + Tb4O7 + Ta2O5 + Nb2O5 100% of which Sc2O3 6.2 Constituents other than ZrO2, HfO2, Sc2O3, Y2O3, Al2O3, CeO2, Yb2O3, Gd2O3, MnO, 0.25 Bi2O3, La2O3, Pr2O3, Nd2O5, Sm2O3, Eu2O3, Tb4O7, Ta2O5 and Nb2O5 Subscripts x and y defining the molar proportions Constituents in the formula (Sc2O3)y(A)x(ZrO2+HfO2)1-xy x 0.000 y 0.056 1-xy 0.944 Other characteristics (monoclinic zirconia + monoclinic hafnia), as mass percentages on a 20-fold basis of the crystallized phases of zirconia and hafnia. Average size of zirconia crystallites (nm) 7 D 10 (µm) 0.22 D 50 (µm) 0.53 D 90(µm) 0.90 The powder of Example 1, which is a product conforming to the first principal aspect of the invention, then underwent a heat treatment step f) of air annealing at 1100°C with a 4-hour holding period at this temperature. The powder obtained at the end of step f), which is a product conforming to the second particular embodiment of the third principal aspect of the invention, has an average zirconia crystallite size of 16 nm and a mass percentage of (monoclinic zirconia + monoclinic hafnia) of 4%, based on the crystallized phases of zirconia and hafnia. Remarkably, the annealing heat treatment very substantially reduces the amount of monoclinic zirconia. The molten product of Example 2 was prepared from the same raw materials as those used for the manufacture of Example 1.and was prepared according to a manufacturing process according to the invention: a) mixing of the raw materials so as to form a starting charge; b) melting of said starting charge in a single-phase Héroult-type electric arc furnace with graphite electrodes, with a furnace chamber of 0.8 m in diameter, a voltage of 160 V, a current of 1500 A and a specific electrical energy supplied of 2500 kWh / T loaded; c) pouring of the molten liquid so as to form a stream, and blowing of compressed dry air, at ambient temperature and at an overpressure of 2 bar so as to break the stream, disperse the molten liquid into droplets and cool these droplets so as to obtain particles of molten product, the cooling rate of the molten material being greater than 15°C / s; d) grinding of the particles obtained at the end of step c), in a jar using zirconia balls with 3% MgO by mass,followed by attrition grinding in a LabStar mill marketed by Netzsch, for 7 hours, of an aqueous suspension consisting of 4000 grams of the powder obtained after grinding in a jar, 1600 grams of Zirmil® Y beads with a median size of 1.25 mm, marketed by Saint-Gobain ZIRPRO, and 5000 grams of demineralized water. After attrition grinding, the resulting suspension is oven-dried at 80°C for 12 hours to obtain a powder. This powder is then deagglomerated using an agate mortar. Table 3 below provides the mass composition of the initial feedstock. [Table 3] Raw materials % mass Zirconia powder 93.4 Scandium oxide powder 6.6 The following table 4 provides the characterizations obtained on the fused particle powder obtained at the end of step d), MnO, Pr2O3, Nd2O5, Tb4O7, Ta2O5 and Nb2O5 expressing the total contents of manganese, praseodymium, neodymium, and terbium oxides,of tantalum and niobium, respectively. [Table 4] Example 2 Chemical analysis, in mass percentages based on the mass of the product (ZrO2+HfO2) + Sc2O3 + Y2O3 + Al2O3 + CeO2 + Yb2O3 + Gd2O3 + MnO + Bi2O3 + complement to La2O3+ Pr2O3+ Nd2O5+ Sm2O3+ Eu2O3+ Tb4O7+ Ta2O5+ Nb2O5 100% of which Sc2O3 6.6 Constituents other than ZrO2, HfO2, Sc2O3, Y2O3, Al2O3, CeO2, Yb2O3, Gd2O3, MnO, 0.25 Bi2O3, La2O3, Pr2O3, Nd2O5, Sm2O3, Eu2O3, Tb4O7, Ta2O5 and Nb2O5 Subscripts x and y defining the molar proportions of the constituents in the formula (Sc2O3)y(A)x(ZrO2+HfO2)1-xy x 0.000 y 0.060 1-xy 0.940 Other characteristics (monoclinic zirconia + monoclinic hafnia), as a percentage by mass on the basis of undetectable zirconia and hafnia crystallized phases Average size of zirconia crystallites (nm) 7 D10 (µm) 0.11 D50 (µm) 0.52 D90 (µm) 0.86 The powder of molten particles after grinding contains an undetectable amount of (monoclinic zirconia + monoclinic hafnia).The manufacturing process of Example 2 does not include an annealing heat treatment step (f), but does involve cooling at more than 15°C / s in accordance with the first particular embodiment of the third principal aspect of the invention. Remarkably, it allows the production of a fused scandium zirconia powder with an undetectable amount of (monoclinic zirconia + monoclinic hafnia). The fused product of Example 3 was prepared from the following raw materials: - zirconia powder with a purity greater than 99.9% by mass and a median particle size of 15 µm; - scandium oxide powder with a purity greater than 99.9% by mass and a median particle size less than 40 µm; - alumina powder with a purity greater than 99.8% by mass and a median particle size of 90 µm.The molten product of Example 3 was manufactured using the same process as that used for Example 2, with the exception of the composition of the starting feed, which included an additive A. Table 5 below provides the mass composition of the starting feed used to manufacture Example 3. [Table 5] Raw materials % mass Zirconia powder 92.8 Scandium oxide powder 6.7 Alumina powder 0.5 Table 6 below provides the characterizations obtained on the molten particle powder obtained at the end of step d), MnO, Pr2O3, Nd2O5, Tb4O7, Ta2O5 and Nb2O5 expressing the total contents of manganese, praseodymium, neodymium, terbium, tantalum and niobium oxides, respectively. [Table 4]. Example 3 Chemical analysis, in mass percentages based on the mass of the product (ZrO2+HfO2) + Sc2O3 + Y2O3 + Al2O3 + CeO2 + Yb2O3 + Gd2O3 + MnO + Bi2O3 + complement to La2O3+ Pr2O3+ Nd2O5+ Sm2O3+ Eu2O3+ Tb4O7+ Ta2O5+ Nb2O5 100% of which Sc2O3 6.7% of which Al2O3 0.5% Constituents other than ZrO2, HfO2, Sc2O3, Y2O3, Al2O3, CeO2, Yb2O3, Gd2O3, MnO, 0.25% Bi2O3, La2O3, Pr2O3, Nd2O5, Sm2O3, Eu2O3, Tb4O7, Ta2O5 and Nb2O5 Subscripts x and y defining the molar proportions of constituents in the formula (Sc2O3)y(A)x(ZrO2+HfO2)1-xy x 0.006 y 0.060 1-xy 0.934 Other characteristics (monoclinic zirconia + monoclinic hafnia), as mass percentages on the basis of undetectable zirconia and hafnia crystallized phases Average size of zirconia crystallites (nm) 7 D10 (µm) 0.15 D50 (µm) 0.59 D90 (µm) 0.99 As is now clear, the invention provides a fused product of scandiated zirconia suitable for use in an electrolyte, manufactured by a simple melting process.This product can advantageously be obtained from recycled raw materials, and in particular from electrolyte manufacturing waste. The invention also provides two simple solutions for obtaining a fine powder of said molten product containing a low amount of (monoclinic zirconia + monoclinic hafnia): cooling at more than 15°C / s, or a combination of cooling at any rate and annealing. Of course, the present invention is not limited to the described embodiments provided by way of illustrative and non-limiting examples. In particular, the molten product according to the invention is not limited to specific shapes or dimensions.

Claims

CLAIMS 1. A solid oxide electrochemical device comprising an electrolyte comprising a polycrystalline molten product of formula (Sc2O3)yAx(ZrO2 + HfO2)1-xy, with 0.030 ≤ y ≤ 0.150, and 0.00 ≤ x ≤ 0.070, and x ≤ y, where A denotes an additive selected from Y2O3, Al2O3, CeO2, Yb2O3, Gd2O3, MnO, Bi2O3, La2O3, Pr2O3, Nd2O5, Sm2O3, Eu2O3, Tb4O7, Ta2O5, Nb2O5 and mixtures thereof, ZrO2+ HfO2+ Sc2O3+ A representing more than 98% of the mass of said molten product, and MnO expressing the total content of the oxides of manganese expressed as MnO, Pr2O3 expressing the total content of praseodymium oxides expressed as Pr2O3, Nd2O5 expressing the total content of neodymium oxides expressed as Nd2O5, Tb4O7 expressing the total content of terbium oxides expressed as Tb4O 7,Ta2O5 expressing the total content of tantalum oxides expressed as Ta2O5, Nb2O5 expressing the total content of niobium oxides expressed as Nb2O5, said molten product comprising, in mass percentages based on the crystallized phases of zirconia and hafnia, an amount of (monoclinic zirconia + monoclinic hafnia) less than or equal to 30%.

2. Device according to the immediately preceding claim, wherein the additive is selected from Al2O3, CeO2, Yb2O3 and mixtures thereof, preferably from Al2O3, CeO2 and mixtures thereof, preferably CeO2.

3. Device according to any one of the preceding claims, wherein 0.130 ≥ y ≥ 0.040 and / or x ≤ 0.

050.

4. Device according to the immediately preceding claim, wherein 0.110 ≥ y ≥ 0.050 and / or x ≤ 0.

030.

5. Device according to the immediately preceding claim, wherein x ≤ 0.

015. 6.A device according to any one of the preceding claims, wherein y = 0.060 or y = 0.

100.

7. A device according to any one of the preceding claims, wherein -x = 0.000 or wherein -x ≥ 0.

005.

8. A device according to any one of the preceding claims, wherein x = 0.010 and the additive is C. eO 2 ou est Al 2 O 3 .

9. A device according to any one of the preceding claims, wherein the molten product has an average zirconia crystallite size greater than or equal to 4 nm, preferably greater than or equal to 5 nm and less than or equal to 10 nm, the average crystallite size being determined by X-ray diffraction on a powder of the molten product using a Bruker Endeavor D8 type apparatus, with the following Debye-Scherrer equation: Kλ 1 180 ^ = ^ ^^ − ^^ xx ( ) cos ^ 10 ^ - K being equal to 0.89, - λ being equal to 1.5418 Angstrom, - B being the full width at half maximum of the zirconia peak present at 2θ equal to 50°, in degrees - b being the full width at half maximum of the peak located at 2θ equal to 35° of a LaB6 standard, reference NIST 660a, analyzed under the same conditions as the melt, and - 2θ being the angle of the maximum intensity of the zirconia peak present at 2θ equal to 50°, in degrees, the full width at half maximum of the zirconia peak present at 2θ equal to 50° of the melt being determined according to the following procedure: - on the diffraction diagram, selection of an area containing the peak located at 2θ equal to 50° and part of the baseline, and not containing any other peaks; - after eliminating the Kα2 line, determination of the width of the zirconia peak present at 2θ equal to 50° using the Highscore + software from Malvern Panalytical, by inserting a peak using the "Insert peak" function at 2θ equal to 50°,then by performing automatic refinement using the "Default Profile Fit" function with a pseudo-Voigt function with a "split width" asymmetry, the full width at half maximum (FWHM) of the peak present on the diffraction pattern at 2θ equal to 50°, B, being the value of the "Total FWHM" parameter, the FWHM of the peak located at 2θ equal to 35°, b, being determined, for the LaB6 standard, following the same procedure.

10. Device according to any one of the preceding claims, wherein said electrolyte is obtained by sintering a particulate mixture comprising a powder having more than 90% by mass of particles into said molten product.

11. Device according to the immediately preceding claim, said powder having a median size D50 greater than 0.1 µm and less than 1 µm, the median size being the particle size corresponding to the percentage, by mass,50% on the cumulative particle size distribution curve of the powder, the particle sizes being ranked in ascending order.

12. Device according to the immediately preceding claim, said powder having a median size D50 of less than 0.7 µm.

13. Manufacturing process comprising the following steps: a) mixing raw materials to form a starting charge; b) melting the starting charge until a molten material is obtained; c) cooling until complete solidification of said molten material, said starting charge being adapted, in step a), to obtain, at the end of step c), a polycrystalline molten product of formula (Sc2O3), y HAS x (ZrO2 + HfO2) 1-x-y , with 0.030 ≤ y ≤ 0.150, and 0.00 ≤ x ≤ 0.070, and x ≤ y, A denoting an additive chosen from Y2O3, Al2O3, CeO2, Yb2O 3,Gd2O3, MnO, Bi2O3, La2O3, Pr2O3, Nd2O5, Sm2O3, Eu2O3, Tb4O7, Ta2O5, Nb2O5 and their mixtures, ZrO2 + HfO2 + Sc2O3 + A representing more than 98% of the mass of said molten product, MnO expressing the total content of manganese oxides expressed as MnO, Pr2O3 expressing the total content of praseodymium oxides expressed as Pr2O3, Nd2O5 expressing the total content of neodymium oxides expressed as Nd2O5, Tb4O7 expressing the total content of terbium oxides expressed as Tb4O7, Ta2O5 expressing the total content of tantalum oxides expressed as Ta2O5, Nb2O5 expressing the total content of niobium oxides expressed as Nb2O5, said molten product comprising, in mass percentages on the basis of the crystallized phases of zirconia and hafnia, an amount of (monoclinic zirconia + monoclinic hafnia) less than or equal to 30%, preferably less than or equal to 10%; d) optionally, grinding of said molten product, preferably to a powder; e) optionally, particle size selection of said molten product;f) before or after step d), optionally, annealing heat treatment of said molten product; then sintering of a particulate mixture comprising said molten product so as to manufacture an electrolyte for a device according to any one of the preceding claims.

14. A manufacturing process according to the immediately preceding claim, wherein in step a), the starting feed contains scandi zirconia.

15. A process according to any one of the two immediately preceding claims, wherein the grinding in step d) and the optional particle size selection in step e) are adapted to obtain a powder having a median size of less than 1 µm, preferably less than 0.7 µm, and preferably greater than 0.1 µm;and - the cooling rate at step c) is greater than 15°C / s.

16. A method according to any one of the three immediately preceding claims, - wherein the grinding at step d) and the optional particle size selection at step e) are adapted to obtain a powder having a median size of less than 1 µm, preferably less than 0.7 µm, and preferably greater than 0.1 µm;and - comprising a said step f).

17. A method according to the immediately preceding claim, wherein step f) is subsequent to step d), and / or wherein the temperature of the annealing heat treatment in step f) is greater than or equal to 800°C.

18. A recycling process for a product to be recycled comprising a material of the formula (Sc2O3)yAx(ZrO2 + HfO2)1-xy, with 0.030 ≤ y ≤ 0.150, and 0.00 ≤ x ≤ 0.070, and x ≤ y, where A denotes an additive selected from Y2O3, Al2O3, CeO2, Yb2O3, Gd2O3, MnO, Bi2O3, La2O3, Pr2O3, Nd2O5, Sm2O3, Eu2O3, Tb4O7, Ta2O5, Nb2O5 and mixtures thereof, ZrO2 + HfO2 + Sc2O3 + A representing more than 98% of the mass of said product to be recycled, and MnO expressing the total content of manganese oxides expressed as MnO, Pr2O3 expressing the total content of praseodymium oxides expressed in the form Pr2O3,; Nd2O5 expressing the total content of neodymium oxides expressed as Nd2O5, Tb4O7 expressing the total content of terbium oxides expressed as Tb4O7, Ta2O5 expressing the total content of tantalum oxides expressed as Ta2O5, Nb2O5 expressing the total content of niobium oxides expressed as Nb2O5, said product to be recycled preferably comprising, in mass percentages based on the crystallized phases of zirconia and hafnia, an amount of (monoclinic zirconia + monoclinic hafnia) less than or equal to 30%, the process comprising steps a), b) and c), and optionally one or more of steps d), e) and f), of a manufacturing process according to any one of the four immediately preceding claims, the starting charge at step a) containing said product to be recycled. 19.A method according to the immediately preceding claim, wherein the product obtained at the end of steps a), b), and c), and optionally one or more of steps d), e), and f), is used in an electrolyte of a solid oxide electrochemical device.

20. A method according to any one of the two immediately preceding claims, wherein the product to be recycled is an electrolyte or a manufacturing waste product of an electrolyte. 21.Powder - having a median size of less than 1 µm, preferably less than 0.7 µm, and preferably greater than 0.1 µm; and - in a molten product of the formula (Sc2O3)yAx(ZrO2 + HfO2)1-xy, with 0.030 ≤ y ≤ 0.150, and 0.000 ≤ x ≤ 0.070, and x ≤ y, where A denotes an additive selected from Y2O3, Al2O3, CeO2, Yb2O3, Gd2O3, MnO, Bi2O3, La2O3, Pr2O3, Nd2O5, Sm2O3, Eu2O3, Tb4O7, Ta2O5, Nb2O5 and mixtures thereof, ZrO2 + HfO2 + Sc2O3 + A representing more than 98% of the mass of said product, MnO expressing the total content of manganese oxides expressed as MnO, and Pr2O3 expressing the total content of praseodymium oxides expressed as Pr2O3, Nd2O5 expressing the total content of neodymium oxides expressed as Nd2O5, Tb4O7 expressing the total content of terbium oxides expressed as Tb4O7, T. a 2 O 5 expressing the total content of tantalum oxides expressed in the form Ta2 O 5 ,Nb2O5 expressing the total content of niobium oxides expressed as Nb2O5, - having, in mass percentages on the basis of the crystallized phases of zirconia and hafnia, an amount of (monoclinic zirconia + monoclinic hafnia) less than or equal to 10%, preferably less than or equal to 5%.