Sesquioxides transitions

The relative stabilities of the dioxides, sesquioxides and monoxides for first period transition metals are given in Figure 7.11(c). The stability of the higher oxidation state oxides decreases across the period. As we will discuss later, higher oxidation states can be stabilized in a ternary oxide if the second metal is a basic oxide like an alkaline earth metal. The lines in Figure 7.11(c) can in such cases be used to estimate enthalpies of formation for unstable oxidation states in order to determine the enthalpy stabilization in the acid-base reactions see below. Finally, it should be noted that the relative stability of the oxides in the higher oxidation states increases from the 3d via 4d to the 5d elements, as illustrated for the Cr, Mo and W oxides in Figure 7.11(d). 

D Aecet found, it is true, -that bottle-glass was, devitrified without changing its weight. That might happen, in -fact, when the oxygen, absorbed by the transition from the oxide of iron to the- sesquioxide, Is equal in weight to the potassa volatilized. 

Trivalent Compounds.—In trivalent vanadium compounds the basic character of the element is well developed, and both normal and oxy-salts of the sesquioxide V203 are well defined, e.g. vanadous sulphate, V2(S04)3, and vanadium oxymonochloride, VOC1. It has been previously mentioned that resemblances between the elements of the A and B Subdivisions of Group V. are mainly restricted to the pentavalent compounds it is of interest to note that the oxychloride has analogues in the trivalent antimony and bismuth basic chlorides, SbOCl and BiOCl. Trivalent vanadium also displays considerable analogy, however, with other trivalent transitional elements, as shown by the following —... 

Perovskites of the type LnMO, (Ln = lanthanide and M = transition metal) may offer interesting features as precursors for supported metal catalysts. For example, careful reduction can be carried out in order to produce a finely dispersed transition metal over the sesquioxides Ln,0,. Also, the flexibility in the perovskite composition allows the preparation of compounds of the type LnM ., M 0, (M and M = different transition metals) or Ln., A,MO, (A - for example an alkaline or alkaline earth metal), which show the unique possibility as precursor of producing well dispersed bimetallic catalyst or doped metal catalyst. 

The strong chemical interaction alumina-rare earth sesquioxide is considered to play a key role in the textural stabilization of the transition aluminas [142,145,170,171,184-187]. In the presence of the supported rare earth oxide, the y-AI2O3 a-AkOs phase transition, and inherently the sintering mechanism, is inhibited. 

The phase diagram for all the lanthanoid sesquioxides is given in Fig. 3-17 and shows the different transformation temperatures. From the diagram it is obvious that promethium, Pm, was the first metal for which the existence of all three polymorphs and the transition temperatures could be established ]39]. For praseodymium, Pr, under atmospheric pressure the C-type structm-e is formed above 500 °C and transforms to A-type above 700 °G. Depending on the ionic radii only for the rare earth metals from Pm to Gd all five polymorphs will be formed. With increasing temperature the order of transition is C B—>A. 

For diode laser pumping, Nd-doped sesquioxides offer several lines in the near-infrared region, with the strongest one being in the region of 820-825 nm, corresponding to the transition of... 

Due to its unique spectroscopic and emission dynamic properties, Nd " ion can be used for laser emission over a wide range of temporal regimes, from CW to very short pulses of below picosecond. The transitions from the two Stark levels of the manifold F3/2 to the Stark levels of the manifolds " ll 1/2, and " Ii3/2, corresponding to the ranges of 0.9, 1.0, and 1.3 pm, respectively, showed pretty large emission cross sections. Various cubic crystalline materials, including garnets and sesquioxides, have been used as hosts for Nd laser emission, which formed the major part of ceramic laser materials. 

For Yb two cases are possible. Divalent Yb has a filled 4f shell, that is, a 4f configuration, and the 4d spectra show the usual doublet with a 3 2 ratio, while for trivalent Yb, 4f the 4d peaks consist of a multiplet. The transition from doublet to multiplet in the 4d spectra of Yb is illustrated nicely in the oxidation of metallic Yb, since metallic Yb is divalent and the sesquioxide is trivalent. Using the parameters of our analysis of metal Yb and sesquioxide of Yb one can conclude that the multiplet 4d spectrum of Yb(acac)TPP and Yb(acac)TPPBrg is clearly indicative of trivalent Yb (Fig. 10.21). 

Aluminum sesquioxide, or a-alumina (a-Al Oj), also called calcined alumina (CA) or burned alumina in the ceramic and refractory industries, is the final product resulting from the thermal decomposition of all aluminum hydroxides. Actually, in the temperature range 1000-1250°C, the exothermic transformation of transition aluminas into a-Al Oj occurs... 

The monoclinic to cubic transition for Bk203 also appears to be irreversible , while the hexagonal-monoclinic transition is readily reversible. This transition behavior is typical for the first four transplutonium sesquioxides. 

The best characterized einsteinium oxide is the cubic (C-type) sesquioxide, prepared by calcining nanograms of a nitrate salt and rapidly analyzing the product by electron diffraction (Haire and Baybarz 1973). A monoclinic form of the sesquioxide was observed when thin films of einsteinram metal were oxidized in oxygen-containing atmospheres at temperatures of 800 1000°C (the direct oxidation of other actinide metals can also yield the monoclinic form of their sesquioxides at temperatures lower than that required for transformation of their C- to the B- forms). This low temperature for the monoelinic form of einsteinium sesquioxide is therefore not comparable to the established transition temperatures reported for the other actinide sesquioxides. The... 

---