Material for protective coatings on chromium oxide forming substrates resistant to high temperatures, method for its manufacture and use The invention relates to a material for the formation of protective layers resistant to high temperatures on chromium oxide forming substrates, to a manufacturing method and to a use of these materials. It is suitable for a use as a chromium evaporation layer for metallic alloys containing chromium in high temperature operation. The material in accordance with the invention is in particular advantageously suitable for use in high temperature fuel cells. As already expressed, the material should be able to be used at high temperatures which can lie in the range between 550 and 1000°C. A direct conversion of chemical energy into electric energy is possible using high temperature fuel cells. In this respect, the cathode/electrolyte/anode unit is a central functional element of fuel cells and" comprises two electrodes - cathode and anode - which are separated from one another by an oxygen conducting electrolyte. To achieve an electrical voltage level acceptable for technical applications, individual cells have to be connected together in series. In the planar concept, the so-called interconnectors or bipolar plates have to be installed between these individual cells with which the gas infeed to the electrodes and the contacting of the individual cells between one another takes place. At the high temperatures, the bipolar plate has to be as electrically conductive and oxidation resistant as possible. In addition, the coefficient of thermal expansion of the metallic interconnector should be relatively low to ensure a good thermomechanical compatibility with the other components of the fuel cell. Only a very few materials can be considered for the manufacture of interconnectors due to a plurality of constraints. The interconnector materials are therefore primarily considered, in particular for uses in planar high temperature fuel cells, which have a high chromium content; they are e.g. alloys on a chromium basis or ferrite steels (alloys on an iron basis containing chromium). However, the problem results with these materials that a chromium(III) oxide layer (Cr203) forms on the surface of the interconnector at the increased operating temperature under an oxidizing atmosphere present there. The chromium oxide reacts at high temperatures with oxygen and water vapor while forming chromium trioxide Cr<>j and chromium oxide hydroxides Cr02(OH)2/CrO(OH)4. These newly formed compounds containing chromium have a high vapor pressure at the operating temperature of the fuel cell and can thus easily move into the cathode. These Cr species react with the cathode material there, which results in a change in its composition and, in the long term, causes the degradation of the catalytic activity of the cathode. This makes a considerable contribution to the performance loss of the fuel cell. Different materials and methods are known from the prior art for the prevention or minimization of the chromium evaporation. Technologies achieve the best results in this respect in which the surface of the interconnectors is covered with so-called protective layers. The interconnectors are, for example, coated with materials containing lanthanum such as LaCrCb. The compound containing lanthanum such as LaCr03 is either applied directly as a protective layer onto the metal surface or the compounds such as La203, LaB6 are applied as reactive layers so that they react with the chromium oxide to LaCrC>3 during operation. This method has the disadvantage that microcracks can form in the LaCr03 layer and can thus not ensure any sufficient protection against the chromium evaporation. A further variant is the coating of interconnectors with chromium-free perovskite layers which are similar to the cathode material. The layers serve both for protection and for cathode contacting. However, they have the disadvantage that a new chemical compound on a chromium base is formed at the border between the layer and the interconnector and can .grow there, said layer causing high degradation of the contact resistance and consequently also of the fuel cell Spinel compounds per se are also suitable as effective materials for protective layers. The generation of Spinel protective layers takes place either by the use of steels such as microalloy elements such as manganese, nickel or cobalt which can form spinel layers from the basic material together with chromium under an oxidizing atmosphere. Spinel compounds can also be formed by the application of layers which contain manganese and which result in spinel compounds under reaction with chromium oxide. The formation of these chromium spinel structures demonstrably results in a reduction in the chromium evaporation. This is, however, still not yet sufficient to ensure a long service life of the fuel cell without degradation since chromium diffusion through the spinel layer containing chromium still occurs. In addition, the Cr(VI) oxide and chromium hydroxide species can continue to be released due to their high Cr portion in the spinel phase. The chromium-free spinel compounds are nevertheless used as protective layer materials. It is thus known from DE 103 06 647, for example, that a gastight, chromium-free spinel layer of the composition Co3-x-yCuxMnyO4 where 0 < x < 1.5, 01200°C) is multiphase and is thereby thermally and chemically unstable. It has been shown that it is particularly favorable if the synthesis is carried out at 1100°C ± 10°C. The mol ratios in which the starting compounds are used are preferably 0.0 to 1.0 (CuO)x for the copper, 0.0 to 1.0 (NiO)y for nickel, 0.0 to 1.0 (Mn203) for manganese and 0.0 to 1.0 for iron relative to the stoichiometric formula (CuO) x(NiO)y (Mn203)2 (Fe203) 1_z. The invention will be explained in more detail in the following with reference to embodiments. Embodiment 1: Manufacture of a compound having a portion of secondary phase below 2.0 mol. %: 2.0268 g CuO, 1.2688 g NiO and 6.7044 g Mn203, which corresponds to the component ratio (CuO) o.6 (NiO) o.4 (Mn203), is weighed in and homogenized in the planetary ball mill over a period of 24 hours. The homogenous powder is screened and calcinated at a temperature of 1100°C for 15 hours. The material manufactured in this manner has a composition, of the spinel phase of Cu0.6Ni0.4Mn2O4. The portion of the secondary phase (MnOx) 1-y +(CuO/NiO)y (1