Tellurium oxide

Te2Fio, and oxide fluorides, e.g. TeFjOTeFs, are also formed during the fluor-ination of tellurium oxides, tellurium, organic derivatives Tellurium forms organic derivatives in the +2 and +4 slates. The +2 compounds are similar to divalent sulphur derivatives although less stable. Tellurium(IV) derivatives are comparatively unstable. 

Cathodic deposition of bismuth(in) telluride films has been reported [224] also on copper and nickel foils, from aqueous nitric acid solutions of bismuth oxide and tellurium oxide in molar ratios of Bi Te = 3 3 and 4 3, at 298 K. The... 

The irreversibility of Te electrodeposition is increased by changing the tellurite solution to pH 10, Figure 9C. At pH 10, the potential difference between deposition and stripping for the 1/1 couple is 600 mV. The origin of peak 0 is still unclear, but appears to be due to changes in an adsorbed layer of tellurium oxide. 

Bismuth nitrate together with sodium sulphide and tellurium oxide have been used to grow bismuth chalcogenide films.162-166 The stoichiometric ratio 2 3 has been confirmed by XPS, EDX, and XRD.162-166 The Bi2Te3 films were rough and consisted of particles with a diameter of 30-100nm, and electron probe microanalysis showed a worm-like network structure.164-166... 

Fig. 22 Changes in the long-wavelength absorption maximum (Amax) a function of tellurium oxidation state.

As an oxide, it is similar to the reddish color of tellurium oxide. Chemically, it behaves similar to tellurium, lead, and bismuth. 

Sorenson etal. [449] have carried out similar studies on electrodeposition of atomic Te layers on Au(lll) surfaces from aqueous solutions. Similarly as in earher works, in this study also, the following techniques were utilized voltammetry, in situ STM, low-energy electron diffraction, and Auger electron spectroscopy. Prior to the deposition, tellurium oxide species coated the surface. Two steps were distinguished in the UPD process. Deposition process was Idnetically slow. 

Tellurium oxide, Te02, is found in rhombic crystals as the mineral tellurite, whilst ferrotellurite is probably an iron tellurate, emmonsite and dividensite being similar compounds. Other naturally occurring tellurates are montanite, a basic bismuth tellurate, and magmlite, a... 

A solution of tellurium-selenium sesquioxide, TeSe03, has been described (p. 357). A basic tellvmum selenate, 2Te02.Se03, analogous to the foregoing sulphur compound, is obtainable from tellurium oxide and selenic acid.4... 

High Temperature Measurements of the Rates of Uptake of Molybdenum Oxide, Tellurium Oxide, and Rubidium Oxide Vapors by Selected Oxide Substrates... 

The rates of uptake of molybdenum, tellurium, and rubidium oxide vapors by substrates of calcium ferrite and a clay loam have been measured in air over a temperature range of 900° to 1500°C. and a partial pressure range of about 10r7 to 10 atm. The measured rates of uptake of molybdenum and tellurium oxide vapors by molten calcium ferrite and of rubidium oxide vapor by both molten clay loam and calcium ferrite were controlled by the rates of diffusion of the oxide vapors through the air. The measured rates of uptake of molybdenum and tellurium oxide vapors by molten clay loam were controlled by a combination of a slow surface reaction and slow diffusion of the condensate into the substrate. 

Figures 4 and 5 show the uptake of tellurium oxide vapor by various sized particles of clay loam and calcium ferrite at 1400°C. Over the temperature and pressure ranges used here, Te02 is the predominant vapor species (4).

For the uptake of molybdenum oxide vapor by the clay loam particles, the uptake of rubidium oxide vapor by the calcium ferrite, and the uptake of the tellurium oxide by both the clay loam and the calcium ferrite, the uptake vs. time plots are curved, and it is not immediately obvious what the rate-determining steps are. Plots of amounts of uptake at constant time and initial rates of uptake vs. particle diameters and diameters squared were therefore made. 

Test of the Uptake Model Based on the Assumption That Diffusion within the Particle is Rate Controlling. As discussed earlier, the plots of molybdenum and tellurium oxide vapor uptake data vs. diameters and diameters squared of the clay loam particles gave inconclusive evidence as to whether the rate-controlling step was a slow rate of reaction at the surfaces of the particles or a slow rate of diffusion of the condensed vapor into the particles. 

Test of Uptake Model Based on a Slow Surface Reaction Combined with Diffusion within the Particle. Since the simple diffusion model is inadequate to describe the uptake behavior of the molybdenum and tellurium oxide vapors by the clay loam particles, a more complex model is required, in which the effects of a slow surface reaction and of diffusion of the condensed vapor into the particle are combined. Consider the condensation of a vapor at the surface of a substrate (of any geometry) and the passage by diffusion of the condensed vapor through a thin surface layer into the body of the substrate. The change in concentration of solute per unit volume in the surface layer caused by vapor condensa-... 

Where the condensation coefficient of the vapor is quite small, as for molybdenum and tellurium oxides condensing on the clay loam particles, the initial rate seems to be determined by the combined effect of a slow reaction and slow diffusion of the condensed vapor into the substrate. An equation has been derived which relates the amount of vapor uptake to the condensation coefficient of the vapor onto the substrate material, the equilibrium uptake of the vapor by the substrate material, and the diffusion constant of the condensed vapor in the substrate material. This equation has yet to be tested extensively in other systems, but it does describe successfully the uptake behavior of molybdenum oxide vapor by the clay loam particles. 

Tellurium occurs in the same periodic classification as sulfur, selenium, and polonium, Tellurium, unlike sulfiu and selenium, has only two allotiopic forms. Due to its 5,r25p4 electron configuration, tellurium, like sulfur and selenium, forms many divalent compounds with covalent bonds and two lone pairs, and d-hybndization is quite common, lo form compounds with tellurium oxidation states of +4 and —6,... 

Di-o-tolyl tellurium bromide anhydride, (C7H7)2Te(Br).0. (Br)Te(C7H7)2, melts with decomposition at 224° to 225° C. on rapid heating. In addition to the usual method of preparation it may be obtained by dissolving equimolecular quantities of di-o-tolyl tellurium oxide and dibromide in toluene. It may be recrystallised from water or chloroform-alcohol. 

Di-o-tolyl tellurium oxide, (CH3.C6H4)2TeO, occurs when the dibromide is treated with 5 per cent, sodium hydroxide. It separates from toluene as small monoclinic columns, sintering at 199° C. and melting at 205° to 206° C., readily soluble in alcohols, sparingly soluble in benzene or toluene. Its aqueous solution has an alkaline reaction. 

Di-m-tolyl tellurium oxide, (CH3.C6H4)2TeO, occurs when the dibromide is heated on the water-bath with ammonium hydroxide. Recrystallised from a mixture of benzene and xylene it sinters at 160° C. and melts at 163° to 164° C., but from xylene alone it sinters at lo4° C. and melts at 155° to 156° C. Its solution in water is strongly alkaline. 

Di-o-phenetyl tellurium oxide, (C2H5O.C6H4)2TeO.—The dibromide in a finely divided state is boiled with concentrated ammonium hydroxide until the colour changes from yellow to white. The product crystallises from toluene as short needles, sintering at 202° C. and melting at 205° to 206° C. The oxide dissolves in chloroform and methyl or ethyl alcohol in the cold, also in warm benzene, toluene, xylene or carbon disulphide it is very sparingly soluble in carbon tetrachloride. 

Di-m-xylyl tellurium oxide, [(CH3)2C6H3]2TeO.—The corresponding dibromide is converted to the oxide by warming with sodium hydroxide on the water-bath. The oxide sinters at 212° C., melts at... 

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