Terbium dioxide

SrH2 STRONTIUM HYDRIDE 1569 Tb02 TERBIUM DIOXIDE 1615... 

Figure 3-26. Surface atom activity difference between terbium dioxide (a) and lead dioxide (b).

Several reduction potentials for californium have been derived both from experimental data and from systematic calculations, and these values are given in Table 11.8. The calculated Cf(iv)/(iii) couple of 3.2 V [127] is in accord with the inability to obtain Cf(iv) in most aqueous media. This value for californium can be compared to the Tb(iv)/Tb(iii) couple of 3.1-3.3 V, the Am(iv)/Am(iii) couple of 2.2-2.S V, and the Cm(iv)/Cm(iii) couple of 3.1 -3.5 V [127,171]. Thus, the ease of forming Cf(iv) should be comparable to forming Tb(iv) or Cm(iv) but more difficult than forming Am(iv) in solution. The solution behavior can be compared to that in the solid state, where the formation of californium dioxide is comparable to preparing terbium dioxide, with both being more difficult to prepare than americium or curium dioxide (see Section 11.7.2). 

The most common valence state in solid compounds is -i-3. A +4 valence state is known for the metal in its dioxide, Tb02, and tetrafluoride, TbF4. Terbium also forms several nonstoichiometric oxides of approximate composition Tb407. 

The bipyridyl-iV,iV-dioxide chromophore has been appended to a calix[4]arene to give L50, and complexed with europium and terbium... 

The lanthanides, unlike the transition metals and the actinides, tend not to form compounds over a range of oxidation states. The +3 oxidation state is characteristic of all of the lanthanides, and the oxide fluorides of formula LnOF (Ln = lanthanide metal) are well known. The less stable oxidation states of + 2 and + 4 are known, but the latter is represented only by the dioxides and tetrafluorides of cerium, praseodymium, and terbium, and no tetravalent oxide fluorides have been reported. 

These elements are usually terpositive, forming salts such as La(N03)g 6H20. Cerium forms also a w ell-defined series of salts in which it is quadripositive. This oxidation state corresponds to its atomic number, 4 greater than that of xenon. Praseodymium, neodymium, and terbium form dioxides, but not quadrivalent salts. 

Cerium, praseodymium, and terbium oxides display homologous series of ordered phases of narrow composition range, disordered phases of wide composition range, and the phenomenon of chemical hysteresis among phases which are structurally related to the fluorite-type dioxides. Hence they must play an essential role in the satisfactory development of a comprehensive theory of the solid state. All the actinide elements form fluorite-related oxides, and the trend from ThOx to CmOx is toward behavior similar to that of the lanthanides already mentioned. The relationships among all these fluorite-related oxides must be recognized and clarified to provide the broad base on which a satisfactory theory can be built. 

Tb-implanted thermally grown silicon dioxide film, and (iii) Tb-doped alumina xerogels fabricated onto monocrystalline silicon. Thus, the terbium-doped alumina xerogel/PAA structure was proposed as a basis for green room-temperature luminescent images [17]. 

Tellurium dioxide complexes with thiourea, 305 Tellurium dithiocyanate complexes, 303 Tellurium hexafluoride complexes, 303 with amines, 304 Tellurium sulfate complexes, 303 Tellurium tetrabromide complexes, 302 Tellurium tetrachloride complexes with acetamide, 304 with amines, 304 with pyridine N-oxide, 304 Tellurium tetrafluoride complexes with amines, 304 with dioxane, 304 Tellurotungstates, 1042 Tempera ture-jump studies molybdenum(VI) complexes, 1259 Terbium complexes p diketones, 1081... 

The higher oxides where the oxygen to metal ratio x in the oxides is in the range of 1.5 to 2.0 are observed for cerium, praseodymium and terbium. These oxides exhibit fluorite-typed dioxides, which do not necessary mean x = 2.0 but usually the x value is slightly smaller than 2.0. Again, the composition of these oxides depends on the temperature, oxygen potential and physical state, besides their history of preparation and treatment [8-11]. 

Single crystals of praseodymium dioxide and intermediate terbium oxides were grown by the hydrothermal method [126]. The pressure in the sample autoclave was smoothly raised and lowered by control of heating and cooling of the autoclave. The rare earth oxide and nitric acid sealed in capsules of thin-walled gold tubing. The pressure of the capsules was raised to 165 MPa and isobarically heated to the run temperature (1003 1143 K). Holding at least for two hours to reach equilibrium,... 

Because the tripositive ions are the most stable for all the rare earth elements in almost all compounds, the thermochemistry of the solid (crystalline) rare earth sesquioxides dominates this chapter. Some rare earths have divalent or tetravalent states, so the chemistry of solid monoxides and dioxides are included. There are also many nonstoichiometric binary oxides of cerium, praseodymium, and terbium. As much as possible, the thermochemistry of these nonstoichiometric binary oxides is included. The stability, phase diagrams, and structures of ternary and polynary... 

In comparing berkelium and terbium, the situation with their configurations seems clearer both form a half-filled f orbital in their dioxides, although there is a large difference in ease of formation and stability of these two dioxides. The dioxide of Bk is very stable and readily forms in air, whereas the formation of TbOj requires highly oxidizing conditions and Tb02 is less stable thermally. 

A simplistic picture of the situation is to have a relationship between the efifective moments of the f-element materials with the probable ion configuration. In this situation, localized f electrons in the metal would have the same moment as localized f electrons in a compound. The moment would depend on the number of such localized electrons regardless of the particular f-element s chemical form. Thus, the number of localized f electrons in Gd metal is seven (4f with three electrons in a ds conduction band), as it is in Cm metal (Sfconfiguration) there are also seven localized f electrons in both gadolinium and curium sesquioxides. Further, terbium and berkelium dioxides have seven localized f electrons. All six materials should have the same moment based on seven, unpaired free-ion electrons. 

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