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Definitions

• This invention relates to novel compositions of matter formed by intercalating heavy metal chalcogenides with certain inorganic or organic compounds hereinafter sometimes referred to as intercalates. More particularly, the inventtion relates to novel compositions including an intercalate and a heavy metal layered chalcogenide, where the chalcogen is selected from sulfur, selenium and tellurium or mixtures thereof, and wherein the heavy metal is selected from titanium, vanadium, zirconium, niobium, hafnium, tantalum, palladium, platinum, and gallium, or mixtures thereof, that form layered chalcogenides with at least certain chalcogens.
• Lubricants are used to reduce this loss and to prevent wear.
• the most generally useful lubricants are petroleum-based materials such as oils and greases.
• the availability of solid lubricants has heretofore been limited to a few layered structures in which the molecular platelets readily slide over each other. Examples of such materials are graphite, molybdenum disulfide, talc and boron nitride.
• Solid lubricants generally have poorer lubricity and are usually employed only where petroleum based lubricants do not have satisfactory properties. Such solid lubricant materials are generally selected for use because of their resistance to environmental conditions that conventional oil and grease lubricants cannot tolerate. For instance oils and greases cannot be used at either temperature extreme, in vacuum or under extremely high loads. Under such conditions the known solid lubricants must be employed even though they possess higher coefficients of friction, higher wear characteristics and lower lifetime than conventional oils and greases. Known solid lubricants also have a tendency to settle out without necessarily reaching the region where they are required, when applied as a suspension in a fluid. When they are applied as a thick paste to overcome the tendency to settle out, it has usually been difficult to force the paste through the narrow clearances normally available between the sliding metal surfaces.
• organic and inorganic compounds can be intercalated, singularly, successively by displacement of a previous intercalate, or collectively, between the layered structures of certain of the heavy metal chalcogenides wherein the chalcogen is selected from sulfur, selenium and tellurium or mixtures thereof, to provide novel compositions of matter.
• certain layered chalcogenides and certain types of inorganic and organic compounds are preferred because they will most readily interact.
• the compounds that have been found to be most readily intercalated are organic and inorganic compounds that (1) are electron donors; (2) are electron acceptors; (3) have substantial polarization interactions, or (4) are capable of d-orbital bonding.
• electron donors are especially advantageous, with those that are strong Lewis :bases, i.e. those exhibiting a pKa of above about 2.0, being preferred.
• chalcogenides containing palladium and platinum and transition elements classified in Groups IV-B and V-B of the Periodic Table of the Elements This definition includes titanium, vanadium, zirconium, niobium, hafnium and tantalum, with respect to all chalcogens.
• suitable layered tellurides also include gallium.
• layered chalcogenides containing mixed cations such as Nb Ta s. Cations selected from among those forming intercalatable layered crystals are preferred but only one such cation need be present.
• a crystal may contain a cation selected from the aforementioned group of palladium, platinum, gallium or Group IV-B or V-B transition elements, together with a second cation which by itself may or may not form a layered crystal with a chalcogen. It is contemplated, however, that the cation present in the largest amount be selected from among those forming intercalatable layered crystals. The other cations need only assume nearly identical positions in the crystal to the first so that layered crystals result.
• Such mixed cation chalcogenides are known to those skilled in the art. All of the foregoing categories of chalcogenides can be intercalated with any of the foregoing groups of inorganic and organic compounds.
• transition metal chalcogenides i.e. the metallic compounds including chalcogenides formed from Group V-B elements and certain other transition element tellurides exhibit unique properties of superconductivity, when these chalcogenides are intercalated, as hereinafter defined.
• the critical temperature of the chalcogenides is raised because of the presence of an intercalate, as defined in this invention.
• the materials exhibit uniquely high anisotropy of the critical field and critical current.
• the usefulness of many of these materials derives from their extremely high structural and electrical anisotropy as well as from the ease with which structure and properties can be taiiored by modification of the layered chalcogenide or the intercalate.
• Intercalated sulfides formed from the transition elements of Group VB of the Periodic Table of the Elements, especially niobium and tantalum, have been found to have especially useful superconductive characteristics.
• the intercalated compositions of this invention are generally useful as X-ray diffraction grating crystals; see copending US. patent application, Ser. No. 54,847, filed July 14, 1970, now US. Pat. No. 3,688,109.
• novel intercalated compositions matter that have been found to be produced when the aforementioned layered heavy metal chalcogenide structures are subjected to a preliminary treatment that is thought to modify its interlayer arrange ment, i.e. cause the chalcogenide to become ordered, as hereinafter defined.
• a preliminary intercalation of ammonia into the chalcogenide structure followed by displacement of the ammonia (or a separate removal and subsequent intercalation) with desired inorganic or organic compounds.
• strong organic Lewis bases such as butylamine having a pKa above about 7.0 can be employed to accomplish the ordering of the crystal.
• chalcogenides formed from elements in Groups IV-B and V-B comprise a preferred grouping as they are most readily intercalated by electron donors.
• chalcogenides and especially sulfides of tantalum and niobium are particularly useful when the intercalate is a Lewis base. More specifically, chalcogenides formed from tantalum and niobium are the only crystals that intercalate weak Lewis bases directly, i.e., without preliminary treatment.
• intercalation compounds other than electron donors
• an electron donor such as a Lewis base that has previously been intercalated or can be used to co-intercalate with an electron donor previously intercalated.
• useful secondary intercalating materials are compounds as set forth in categories (2)(4).
• Electron donors Molecules that have low electronegativity. Electron donors can be subdivided into categories. One major category comprises Lewis bases, i.e., molecules which possess an unshared electron pair. Ammonia and various amines are examples of this category. Another category comprises 11' donors, molecules in which the loosely held electrons reside in the 1r orbitals of the donor. Tetramethylparaphenylenediarnine is an example of this category. In the present disclosure, electron donors, especially Lewis bases, and more especially strong Lewis bases, are the preferred intercalates. Electron donors intercalate most readily in electron poor layered chalcogenides, i.e., those possessing an accessible (both spatially and energetically) unoccupied orbital.
• Electron acceptors can be subdivided in the same manner as donors, i.e., there are Lewis acids and 1r acceptors. Electron acceptors intercalate most readily in electron rich layered chalcogenides, possessing an accessible (both spatially and energetically) occupied orbital.
• Another class of molecules which react with layered chalcogenides to form intercalation compounds are those that possess a substantial electric dipole either permanent or induced.
• Molecules possessing a permanent dipole include an image dipole of opposite polarity in the layer. This occurs principally in metallic layered chalcogenides where there are free electrons which can move in response to the electric fields of the dipole.
• the dipole of the intercalate may result from ionicity or simply from the separation of charge within the molecule.
• a weaker interaction of this same nature occurs if the molecule itself is highly polarizable. In that case spontaneous fluctuations in the charge density in the metallic layer induces fluctuations of opposite sign in the molecule leading to a stabilizing attractive intercalation of the van der Waals type.
• Dye molecules are especially good in this regard.
• a fourth class of molecules which react with layered chalcogenides to form intercalation compounds are molecules which possess accessible d orbitals.
• the d orbitals of atoms extend well beyond the s and p orbitals and so when they are of appropriate energy, can readily interact with orbitals of the chalcogenide to form chemical bonds.
• Such compounds usually contain sulfur, phosphorus, arsenic, or heavy metal atoms such as mercury.
• Lewis base compounds classified among the electron donors intended to be included in this invention are those organic compounds that either (1) contain at least one non-carbon (hetero) atom selected from Groups V-A and VI-A of the Periodic Table of the Elements, or (2) bear a negative charge compensated for by a metallic counterion.
• Preferred noncarbon elements include oxygen, nitrogen, phosphorus and sulfur.
• Nitrogen-containing organic compounds, i.e., nitrogenous Lewis bases, such as amines, amides, heterocyclic bases and amidines, have been found to be especially useful for intercalation. Ketones and aldehydes are also advantageous. It is also preferred that the ratio of carbon atoms to functional sites, i.e. functional groups or hetero atoms, in these Lewis base organic compounds be no greater than 50 to 1 and more preferably 18 to 1.
• Various organic polymers that are Lewis bases are contemplated as being useful, and especially those polymers having a molecular weight of less than 5000.
• the opening of the dichalcogenide layers appears to require the expenditure of a specific amount of energy per unit area. Therefore there must be a minimum number of molecule-layer interactions of a given strength per unit area before the energy of the intercalated assembly is lower than that of the unintercalated assembly (i.e. molecules outside, lattice closed).
• a specific basic group in a small molecule might be sufficient to form a stable intercalation complex but the same basic group might not be sufiicient for a large molecule, i.e. large in the sense that it would obscure much of the dichalcogenide plane and in doing so reduce the number of molecule layer interactions below the minimum per unit area required.
• an intercalated species that is able to pack closely in a highly ordered arrangement is favored because the crystal is then further stabilized by intermolecular interactions.
• Heavy metal chalcogenides can be prepared by any of a number of conventional methods known to those skilled in this art; see for example J. Inorg. Nucl. Chem., vol. 24, pages 257 to 263 (1962); J. Phys. Chem. Solids, vol. 26, pages 1445-1458 (1965); and Handbook of Preparative Inorganic Chemistry, vol. II, page 1327, 2nd ed., Academic Press (1965).
• tantalum disulfide for example, has been prepared in both crystal and powder form.
• the powder form was obtained by direct combination of the elements in evacuated quartz ampoules at elevated temperatures.
• the preparation included slowly heating, in a stoichiometric ratio of 1:2, a few grams of ultrapure tantalum wire and ultrapure sulfur (such as in the form of chips) in quartz ampoule which was evacuated and then sealed under vacuum.
• Bulk tantalum was found to be preferable to powder because the latter tends to absorb water from the air.
• the quartz ampoule was placed in a furnace and the furnace temperature was raised very slowly to 950 C.
• the sulfur had time to react with the bulk tantalum and was consumed so the vapor pressure did not rise to a dangerous level. This procedure required about 3 weeks.
• the oven was allowed to remain at that temperature for a week or two. This insured complete reaction of the components and a homogeneous combination of tantalum and sulfur as tantalum disulfide.
• the tantalum disulfide prepared in this manner was a black, highly crystalline, free-flowing powder.
• tantalum disulfide crystals have been prepared by iodine vapor transport, i.e., charging a quartz ampoule with a few grams of TaS and 5 m. I per cc., heating the ampoule in a temperature gradient from 800 to 700 C. (Under these conditions, the material was transported at rates of the order of a gram or two per week. Higher rates were obtained by going to higher hot end temperatures and larger tubes). After several days the oven was turned off and allowed to cool slowly to room temperature. It is preferable to cool slowly so as to produce a phase that will intercalate readily. Fast cooling may form polymorphs or disordered phases of Ta-S that are more difficult to intercalate.
• Titanium disulfide powder of reasonably good quality was prepared in approximately the same manner as that described for tantalum disulfide. The principle difference was that the maximum temperature required to complete the reaction was substantially less than 950 C. It was found that a maximum temperature of 650 C. was adequate when employing the same reaction times as those employed for tantalum disulfide. It has been reported in the literature that when titanium disulfide is prepared at higher temperatures, it is not stoichiometric.
• Niobium disulfide, niobium ditelluride, niobium diselenide, tantalum diselenide, tantalum ditelluride, titanium diselenide, and titanium ditelluride have been prepared by the procedures set forth at column 5, line 58 et seq. and column 6, line 1 8 et seq. Similar preparation techniques are generally applicable to the formation of all the chalcogenides disclosed herein. Variations in temperature and time for optimum chalcogenide formation will be obvious to those skilled in the art.
• Intercalation of chalcogenides with organic compounds Intercalatio-n of the chalcogenides with the organic compounds set forth herein can be accomplished by a number of procedures.
• the most broadly applicable method especially suitable for intercalating a Lewis base having a low melting point, has involved immersing the chalcogenide crystals in a liquid phase (neat melt) of the organic compound for a time sufiicient to cause intercalation. Sufficient prolongation of the residence time creates an equilibrium condition. Modifications in pressure or temperature also affect the rate of intercalation, with higher temperatures and pressures accelerating the equilibrium condition. Lower reaciton temperatures are preferred however because at higher temperatures, undesirable side reactions may occur.
• Solution technique The organic compound to be intercalated is dissolved in a suitable solvent, such as benzene or other organic solvent that is itself intercalated less rapidly than the organic compound.
• a suitable solvent such as benzene or other organic solvent that is itself intercalated less rapidly than the organic compound.
• the inorganic crystals to be intercalated are immersed in this solution at an appropriate temperature, that may be elevated.
• Vapor phase intercalation The chalcogenide crystals to be intercalated are placed in the vapor of the organic compound to be intercalated.
• Solid phase intercalation The chalcogenide crystals to be intercalated are covered and mixed with the compound to be intercalated at an appropriate, perhaps elevated, temperature.
• each of the aforementioned techniques are similar in that the intercalation is allowed to proceed a suitable length of time before the crystals are separated from the excess compound.
• the suitable time will depend on the amount of material one wishes to place inside the crystal.
• the ampoule was heated in an oil bath at 200 C. for a few minutes.
• the intercalation proceeded with such rapidity that the swelling of the tantalum disulfide was easily detected by the eye.
• the container was opened and the crystals washed briefly with dischloromethane. The weight gained corresponded to the product TaS (pyridine) /2. It was found that intercalation proceeded with equal facility whether accomplished immediately after formation of the chalcogenide or after open exposure of the chalcogenide to air of several days prior to intercalation. The intercalation also proceeds at lower temperatures but takes more time. At 150 C. the reaction is completed in one day.
• Table I illustrates compounds prepared by the aforementioned sealed tube technique. This procedure, as well as the other procedures set forth above, can be generally applied to combining all the inorganic and organic intercalates with the chalcogenides as set The temperatures cited above can be decreased by increasing the duration of reaction.
• Table H contains representative data illustrating interplanar spacing of intercalated crystals, increase in interplanar spacing on intercalation, moles of intercalate/mole of tantalum disulfide, and critical temperature (K.) for tantalum disulfide intercalated with various organic compounds.
• K. critical temperature
• Z-G-dimethoxypyridine 33 2,6-dimethylpyridine- 20 2. 15 3,5-dimethylpyridine. 20 2. 2-ethylpyridinn 29 3. 2O 3-ethylpyridiue 11. 34 5. 34 29 4. 55
• the ratio of intercalate to chalcogenide within the present invention can be varied broadly. Thus, stoichiometric quantities of intercalate can be introduced. Conversely, lesser amounts are also contemplated.
• Chalcogenides in which the intercalate is included in every other van der Waals gap rather than in every van der Waals gap (second stage composition) have been prepared simply by taking a reduced amount of intercalate in combination with the layered chalcogenide.
• An example in which such a compound has been formed in tantalum disulfide (pyridine) This compound was prepared by taking 1 gm. tantalum disulfide and a A equivalent of pyridine and placing them in a Carius tube, freezing the components in liquid nitrogen, evacuating the tube, sealing it, and then heating it to 200 C. for 15 days. No work up was necessary.
• the color is due to the presence of a low valence species of the metal which has been extracted from sites between the layers. This is further sup ported by the fact that repeated washing with ammonia soon exhausts the color.
• this ordering of the chalcogenide can also be accomplished by annealing procedures, especially when the annealing is continued for a prolonged period such as a few days at temperatures up to the formation temperature of the chalcogenide.
• Such prolonged high temperature conditions after initial cooling following conventional formation of the chalcogenide, apparently enable the reaction of the heavy metal and the chalcogen to proceed to completion.
• annealing removes the pinning centers that tend to hold the layers together more strongly than do the Van der Waals forces so that intercalation proceeds more readily.
• Other methods of ordering the chalcogenide interlayer structure are contemplated.
• Intercalation of strong Lewis bases such as ammonia can be accomplished by the methods outlined above for other inorganic intercalates. In addition, the following procedure has been found to be especially useful for ammonia.
• a small quantity, e.g., a few grams, of the chalcogenide to be intercalated was placed in a Carius tube. Ammonia. in excess, was condensed over the chalcogenide. The ammonia was then frozen, the tubes was sealed. and placed in a bomb containing liquid ammonia such that the temperature could be increased to 70 C. At 70 C. the intercalation with ammonia generally was found to be completed overnight. Longer periods are required when lower temperatures are employed. The bomb was frozen in Dry Ice and the tube removed. (Under this condition the bomb can be opened without danger.) While still frozen, the tubes were opened and the excess ammonia was allowed to evaporate, leaving the layered chalcogenide intercalated with ammonia.
• the chalcogenide/ammonia complex was added directly to a refluxing solution of a secondary intercalate such as, pyridine. It is most advantageous for the solution to contain sutficient intercalate to provide an amount in excess of the moles of chalcogenide being intercalated.
• a secondary intercalate such as, pyridine.
• sutficient intercalate to provide an amount in excess of the moles of chalcogenide being intercalated.
• subsequent intercalation with pyr idine was obtained by refluxing the titanium disulfide/ ammonia complex for approximately 24 hours in a stoichiometric excess of pyridine. At the end of 24 hours the titanium disulfide powder appeared to have stopped swelling, an indication that the intercalation of pyridine was complete. The powder was then removed and Washed with methylene chloride.
• the intercalated ammonia can be removed by heating in a vacuum and the secondary intercalation accomplished by the aforementioned sealed tube procedure.
• TiS prepared as described earlier is treated with NH also described earlier to produce TiS (NH This compound was added directly to a stoichiometric excess of boiling pyridine without undue exposure of air or moisture. The mixture was refluxed for 24 hours. The product was found to be TiS (pyridine)l 2. This material cannot be prepared by direct treatment of TiS with pyridine but can only be prepared by the above displacement reaction.
• Tis -(acetamide) can be prepared by treating TiS (NH with a large stoichiometric excess of a saturated benzene solution of acetamide at 50 C. for two days. The product is worked up with a suitable solvent such as methylene chloride. Protic solvents such as methanol are usually less satisfactory due to the tendency of TiS to undergo slow hydrolysis.
• the preceding illustrates the use of the strong Lewis base ammonia as a pre-intercalate for accomplishing ordering of the crystal. Strong organic Lewis bases are also useful for this purpose.
• 2 grams of tantalum disulfide were intercalated with aniline by the aforementioned sealed tube technique.
• the resulting intercalated crystal was placed in a large excess of refluxing pyridine, at about 115 C., for 24 hours. Examination of the crystal revealed substantially complete displacement of the aniline by the pyridine.
• intercalation compounds containing an ordered mixture of intercalates for example, pyridine in one gap and ammonia in the next gap, can be prepared by treating such a second stage compound (TaS (pyridine)%) in the sealed tube type process with the other intercalate (at room temp. for 3 days) to give the following type of intercalated chalcogenide:
• Superconductivity is that property of many compounds at temperatures near absolute Zero wherein their electrical resistivity vanishes. Substances having superconductive characteristics have found application in magnets, particle accelerators, computer memory units and the like.
• Superconductivity is conventionally detected by placing a sample of the compound inside one of two equivalent coils which are so connected that the eifective mutual inductance between the pair and a third coil which surrounds them is zero. The onset of superconductivity in the sample changes the coupling between the coil in which it is placed and the aforementioned third coil. When this occurs the net mutual inductance between the pair of coils and the surrounding (3rd) coil is no longer zero. A voltage is then developed across the pair and is measured using a phase sensitive detector.
• compositions of this invention are a series of transition metal chalcogenides containing any of the inorganic and organic intercalates set forth supra, that display modified superconductivity from that known to be demonstrated by the chalcogenide per se.
• Specific chalcogenides within this definition include NbS NbSe NbTe TiTe VSe TaTe PdTc TaS and TaSe
• Other particularly advantageous compositions are obtained by intercalation of other of the aforementioned metallic chalcogenides.
• intercalated chalcogenides exhibited critical temperatures higher than that known for the unintercalated chalcogenide.
• all the intercalated chalcogenides have been found to be useful because of uniquely high anisotropy of their critical field and current and because of the weak coupling between layers.
• composition of matter comprising:
• the heavy metal element being selected from the group consisting of titanium, tantalum, niobium, gallium, and mixtures thereof;
• the chalcogen being selected from the group consisting of sulfur, selenium and tellurium;
• the intercalate being selected from at least one of the group consisting of ammonia, hydrazine, amines, nitrogencontaining heterocyclic bases and halogen salts thereof, amides, and thioamides of not more than about thirty carbon atoms;
• composition of matter according to claim 1, wherein said intercalate has a ratio of carbon atoms to heteroatoms of no greater than 18:1.
• composition of matter according to claim wherein said intercalate has a pKa of greater than 7.
• composition of matter according to claim wherein said intercalate is an amine
• composition of matter according to claim wherein said intercalate is an amide.
• composition of matter comprising:
• intercalate is selected from the group consisting of ammonia, hydrazine, amines, nitrogen-containing heterocyclic bases and halogen salts thereof, amides, and thioamides of not more than about thirty carbon atoms.
• composition of matter according to claim 6, wherein said intercalate has a ratio of carbon atoms to heteroatoms of no greater than 18: 1.
• composition of matter according to claim 6, wherein said intercalate is ammonia, hydrazine or amine.
• composition of matter according to claim 6, wherein said intercalate is a nitrogen-containing heterocyclic base.
• composition of matter comprising:
• intercalate containing niobium disulfide, wherein the intercalate is selected from the group consisting of ammonia, hydrazine, amines, nitrogen-containing heterocyclic bases and halogen salts thereof, amides and thioamides of not more than about thirty carbon atoms.
• a composition of matter according to claim 12, wherein said intercalate has a ratio of carbon atoms to heteroatoms of no greater than 18:1.
• composition of matter according to claim 12, wherein said intercalate is ammonia, hydrazine or amine.
• composition of matter according to claim 12, wherein said intercalate is a nitrogen-containing heterocyclic base.
• composition of matter comprising:
• intercalate a structural layered intercalate containing titanium disulfide, wherein the intercalate is selected from the group consisting of ammonia, amines, nitrogen-containing heterocyclic bases and halogen salts thereof, amides, and thioamides of not more than thirty carbon atoms, with the proviso that when the intercalate is an amide, the titanium disulfide is pretreated with ammonia or a basic amine.
• said intercalate is an amine
• composition of matter according to claim 17, wherein said intercalate is a nitrogen-containing heterocyclic base.

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• 1970
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