Transition oxides

Kashiwazaki67 has fabricated a complementary ECD using plasma-polymerized ytterbium bis(phthalocyanine) (pp—Yb(Pc)2) and PB films on ITO with an aqueous solution of 4M KC1 as electrolyte. Blue-to-green electrochromicity was achieved in a two-electrode cell by complementing the green-to-blue color transition (on reduction) of the pp—Yb(Pc)2 film with the blue (PB)-to-colorless (PW) transition (oxidation) of the PB. A three-color display (blue, green, and red) was fabricated in a three-electrode cell in which a third electrode (ITO) was electrically connected to the PB electrode. A reduction reaction at the third electrode, as an additional counter electrode, provides adequate oxidation of the pp Yb(Pc)2 electrode, resulting in the red coloration of the pp—Yb(Pc)2 film. 

Table Electrical Properties of Some Transition Oxides... 

In addition to gibbsite there are other routes to manufacture Al(OH>3 and the consecutive transition oxides. One is the precipitation of Al(OH)3 from aluminum salts by adjusting the pH between 7 and 12 by adding bases. Precipitation at elevated temperatures and high pH leads to formation of bayerite, whereas at lower pH pseudoboehmite and subsequently boehmite are formed. By heating, these materials can be converted to the active transition aluminas. 

The authors [100] investigated mechanochemical synthesis of these perovskites using transition oxides in different oxidation state and lanthanum oxide or carbonate as initial compounds. The activated samples were then heated at temperatures above 500°C. The degree of interaction was shown to depend upon the oxidation degree of transition metal ions in oxides. The higher oxidation degree, i.e. the acidity of oxide, is preferable. 

One aspect of Mossbauer spectroscopy that has not been widely exploited in phase transformation studies is time resolution. Studies with conventional techniques are possible over a wide range of time scales, starting from the intrinsic time scale of the Te Mossbauer effect (t <= 10 s) to investigate processes such as electron transfer, to time scales of t 10 s to measure diffusion, to longer timescales of t > 10 s to study phase transitions, oxidation and other chemical reactions. 

Table 4.S gives the type of semiconductivity found in common transition oxides and sulfides. Many of these will be recognized as catalytically...

Several types of A1203 have been reported for alloys forming alumina layers [1-4]. At high temperatures the metastable (transition) oxides y, 5, and 0-Al2O3 will transform to the a-AI203 according to the following sequence [3,5] ... 

Differential Scanning Calorimetry (DSC) thermal transitions oxidation onset time and temperature, melting point, crystallinity... 

Fig. 2 shows a similar comparison of temperature dependence monitored by means of low temperature EPR spectroscopy. PSIl membranes were supplied with DCMU to ensure only one turnover of S-state and illuminated at four different temperatures. In control membranes (panel A), the multiline and g=4.1 signals both arising from the Mn cluster in S2 state were well induced above -70 C (a,b,c) but not below -155 C (d). This is consistent with the generally accepted threshold temperature for to S2 transition (oxidation of Mn cluster). It is of note that in spectrum Ad, a clear g=3.01 signal... 

No structure suggestions have been made so far for thc transition oxides which show only few and unclear X-ray diffraction patterns. 

Fig. 8. Partial scheme of aluminium hydroxide decomposition (without the transition oxides formed at higher temperatures and the end product corundum)...

ScTiOj and LiNbOj. These compounds share many features with non-transition-metal oxides. They have a filled valence band of predominantly 02p character and a gap between the valence band and an empty conduction band. Typical band gaps are h-A eV. Unlike transition-metal oxides with 0 < n < 10, stoichiometric, post-transition-metal oxides ZnO, SnO, and transition-metal oxides may be reduced but not oxidized. The post-transition oxides ZnO, In Oj, SnOj, as well as the majority of transition-metal oxides, are active in redox reactions since the electron configuration of the solid may be altered. However, the reaction with oxidizing species such as Oj is expected only with samples that have been bulk reduced or where the surfaces have been made oxygen deficient (Calatayud et al. 2003). The reduction of post-transition oxides as a rule leads to the formation of free carriers, which greatly increase the metal-oxide conductivity, a fact that is crucial for sensor applications. 

Metal nitrides are transition metal materials (titanium, vanadium, and molybdenum) that are receiving attention for pseudocapacitive study because they exhibit high electronic conductivities compared to transition oxides. Liu et al. [94] studied molybdenum nitride (Mo N) and showed that... 

The cathode/electrolyte interface has received much less attention than the anode/electrolyte interface, mostly because carbonate electrolytes are electrochem-ically stable with conventional lithium transition oxide materials, such as LiCo02, LiMn204, and LiFeP04. However, the cathode/electrolyte interface is acmally still problematic. The catalytic effect of the transition metal oxide will lead to parasitic reactions of electrolyte on the surface of the cathode. Moreover, as some reactive species in the electrolyte (such as HF, PF5 and POF3 in LiPF -based electrolytes)... 

The physical influences of rare-earth elements on rates and direction of growth and structural characteristics of oxide scales mainly result fi om the incorporation of the rare-earth compounds in the scale. Other influences relate to their capacity to nucleate more uniform fine-grained oxide, inhibit the formation of transitional oxides and promote, for instance, Cr203 formation where it would not normally be expected, as exemplified in studies by Stringer et al. (1972), Whittle et al. (1977), Rhys-Jones et al. (1987) and Rhys-Jones and Grabke (1988). 

A chemomechanical system can be defined as one that is used to obtain macroscopic mechanical energy caused by microscopic deformation in response to changes in an external environment it is also considered to be a system for obtaining large deformations effectively by using microscopic mechanical energy. Polymer gels can be functional polymers that possess complex system functions similar to those of biomaterials. Thus, they are potentially useful chemomechanical materials and various studies are underway today. Chemomechanical systems actuate by phase transition, oxidation-reduction, chelation, and formation of complexes between polymers. They are classified as follows ... 

Julien C, Gorenstein A (1995) R D of lithium microbatteries using transition oxide films as cathodes. J Power Sourc 15 373-391... 

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